As discussed above, the current PAMS network design calls for two sites (a Type 2, and a Type 1 or Type 3) per PAMS area. In their report (U.S EPA, 2011f), the CASAC AMMS found "that the existing uniform national network design model for PAMS is outdated and too resource intensive," and recommended "that greater flexibility for network design and implementation of the PAMS program be transferred to state and local monitoring agencies to allow monitoring, research, and data analysis to be better tailored to the specific needs of each O3 problem area." While stating that the current PAMS objectives were appropriate, the AMMS report also stated that "objectives may need to be revised to include both a national and regional focus because national objectives may be different from regional objectives." The NACAA MSC also advised the EPA that the existing PAMS requirements were too prescriptive and may hinder state efforts to collect other types of data that were more useful in understanding their local O3 problems.
The EPA agrees with CASAC that the PAMS objectives include both local and national objectives, and believes that the current PAMS network design is no longer suited for meeting either sets of objectives. As part of the PAMS evaluation, it was determined that at the national level the primary use of the PAMS data has been to evaluate photochemical model performance. Due to the locations of the current PAMS areas and the current network design, existing PAMS sites are clustered along the northeast and west coasts leading to significant redundancy in these areas and very limited coverage throughout the remainder of the country (Cavender, 2014). The resulting uneven spatial coverage greatly limits the value of the PAMS data for evaluation of model performance. CASAC (U.S. EPA, 2011f) noted the spatial coverage issue and advised that the EPA should consider requiring PAMS measurements in areas in addition to "areas classified as serious and above for the O3 NAAQS to improve spatial coverage." The EPA also agrees with CASAC and NACAA that the PAMS requirements should be revised to provide monitoring agencies greater flexibility in meeting local objectives.
The EPA proposed changes to the network design requirements to better serve both national and local objectives. The EPA proposed a two part network design. The first part of the design included a network of fixed sites ("required PAMS sites") intended to support O3 model development and the tracking of trends of important O3 precursor concentrations. The second part of the network design required states with O3 non-attainment areas to develop and implement Enhanced Monitoring Plans (EMPs) which were intended to allow monitoring agencies the needed flexibility to implement additional monitoring capabilities to suit the needs of their area.
To implement the fixed site portion of the network design, the EPA proposed to require PAMS measurements at any existing NCore site in an O3 nonattainment area in lieu of the current PAMS network design requirements. The NCore network is a multi-pollutant monitoring network consisting of 80 sites (63 urban, 17 rural) sited in typical neighborhood scale locations and supports multiple air quality objectives including some of the objectives of the PAMS program including the development and evaluation of photochemical models (including both PM2.5 and O3 models), development and evaluation of control strategies, and the tracking of regional precursor trends.
The EPA recognized that in limited situations existing NCore sites may not be the most appropriate locations for making PAMS measurements. For example, an existing PAMS site in an O3 nonattainment area may be sited at a different location than the existing NCore site. In this case, it may be appropriate to continue monitoring at the existing PAMS site to support ongoing research and to maintain trends information. To account for these situations, the EPA also proposed to provide the EPA Regional Administrator the authority to approve an alternative location for a required PAMS site where appropriate. The EPA also solicited comments on alternative frameworks using other benchmarks such as attainment status or population to ensure an appropriately sized fixed PAMS monitoring network. The EPA received several comments on the proposed changes to the network design, primarily from state and local monitoring agencies. The following paragraphs summarize the major comments made on the proposed network design, our response, and final network design requirements.
Most commenters agreed with the need to revise the existing network design. One commenter agreed that "requiring PAMS monitoring at already existing NCore locations will benefit national and local objectives to understand ozone formation and would also provide significant cost efficiencies." Another commenter stated that they supported the proposed changes, "especially the flexibility provided by EMPs designed to meet local objectives and achieve a better understanding of photochemical precursors" Another commenter supporting the changes stated that the "proposed network revision will provide states the flexibility to use their resources effectively." One commenter stated that the proposed changes "reflect a more efficient use of state and local monitoring resources by availing monitoring agencies of existing NCore infrastructure to fulfill PAMS requirements."
A number of concerns were also raised with the proposed network design. Several commenters stated that the proposal "would drastically reduce the PAMS network in the Northeast." One commenter stated that "this is not acceptable for the Northeast and Mid-atlantic Corridor, which requires monitoring of the complex transport from multiple large metropolitan areas in the region." One commenter recognized that the EPA had intended to allow states to use EMPs to address upwind and downwind data needs, but raised concerns that states with historically important upwind and downwind sites in the Ozone Transport Region (OTR) may not be required to develop an EMP since those sites would be in states that are attaining the O3 NAAQS. One commenter suggested that "the EPA consider the entire OTR when designing a PAMS network rather than pockets of nonattainment areas in the region." The EPA agrees that the reduction of sites in the OTR is a potential issue and that many important existing PAMS sites would not be part of the required PAMS sites based on the proposed network design. As noted by several commenters, the EPA intended the state directed EMPs to give states flexibility in determining data needed to understand local O3 formation, including transport in the Northeast. However, the EPA also agrees that as proposed many states in the OTR would not be required to develop EMPs and, therefore, may not be provided PAMS resources. To address these concerns and ensure adequate network coverage in the OTR, the EPA is adding a requirement that all states in the OTR develop and implement an EMP regardless of O3 attainment status. This change will help ensure that an EMP appropriate for the entire OTR can be implemented.
Concerns were raised by some states that existing NCore sites may not be the most appropriate location for making PAMS measurements. One commenter noted that their NCore site was inland but that their "most significant ozone problems occur along the shoreline due to transport along the lake", and that "the NCore site cannot provide insight into these important lakeshore ozone processes." Another commenter stated that "while it was laudable to leverage sites where data is already being collected, it is unclear whether NCore sites adequately meet the objectives of the PAMS program", and that "the current NCore network may not be adequate to depict boundary conditions or areas of maximum emissions." One commenter stated that "in some nonattainment areas an NCore site may be an appropriate location for a PAMS monitor, but in other areas it would be preferable to install the PAMS monitoring in a location downwind of a source region where higher ozone exposures occur" and that "State and local boundaries should not be part of the network design criteria." One commenter noted that while the EPA had proposed to allow waivers, it was unclear if waivers would be allowed where the alternative site was in a different CBSA or State than the required PAMS site. As stated in our proposal, the EPA recognizes that in some cases existing PAMS sites (or other sites) may be better suited to meet local and national data needs. For this reason, we had proposed to allow waivers in these situations. We do agree that it is appropriate in some cases to allow these waivers to cross CBSA and state boundaries. Therefore, we have added specific language to the final waiver provisions to clarify that waivers can be allowed to cross CBSA and state boundaries. Where a monitoring agency receives a waiver from siting a monitor in reliance on a monitor operated by a different monitoring agency (e.g., across state lines), the waiver will be conditioned on the monitor being properly included in the other agency's network plan, and operated in accordance with the requirements of Part 58, including the relevant appendices.
In addition to the concerns raised about closing important existing PAMS sites discussed above, some commenters raised concerns that many of the newly required PAMS sites would be in locations that were expected to attain the revised O3 NAAQS soon after the new sites would be installed. One commenter noted that "requiring marginal nonattainment areas to install PAMS sites would result in a large undertaking at an area that would most likely be back in attainment at or around the time the PAMS site started collecting data." One commenter stated that by tying the network requirement to NAAQS attainment "threatens to underserve areas that are very close to exceeding the revised ozone NAAQS and results in significant gaps in the spatial coverage of the PAMS network" and "has the potential to introduce undesirable uncertainty on the size and spatial extent of the PAMS network over the long term." Another commenter was concerned that the proposed network would be unstable, and would experience frequent changes as areas came into attainment or went out of attainment thus reducing the value of the data collected, and resulting in inefficient use of resources. One commenter noted that "a more stable monitoring network design will allow for the examination of trends from spatially robust, long running sites and will allow states to firmly establish the infrastructure costs."
The EPA noted in the proposal that the size and locations of the proposed required PAMS network is sensitive to the level of the revised O3 NAAQS and future O3 concentrations. We recognize and agree that if current downward trends in O3 concentrations continue, many initially required sites may no longer be required to make PAMS measurements soon after the sites were installed. Non-required sites could be closed, soon after being installed, at the state's discretion. We agree this would result in an inefficient use of resources. We also note that if these sites were closed following a potential reclassification to attainment, the loss of those sites could lead to a network with poor spatial coverage. Therefore, the EPA is making changes to the proposed revisions to the network design to improve the stability of the fixed site network. As explained below, the final requirements are based on options for which we requested comments in the proposal and the comments we have received.
We requested comments on additional options to define the fixed PAMS network component of the new network design. These options were further discussed in a memorandum to the docket (Cavender, 2014). One option discussed was to require PAMS measurements at all NCore sites irrespective of the O3 attainment status of the area. One commenter noted that "requiring PAMS monitoring at all NCore sites, regardless of ozone attainment status, provides the most spatially robust and stable monitoring network." We noted that this requirement would result in a network of approximately 80 sites, which would be larger than the current network. In the supporting memorandum, we noted that a fixed network of 80 sites would strain existing resources and would not allow adequate resources to implement the state directed EMPs.
Another option discussed in the proposal included requiring PAMS measurements at NCore sites in O3 nonattainment areas with a population greater than 1,000,000. We noted that this option would result in a network of between 31 and 37 sites depending on the level of the revised O3 NAAQS. We also noted that focusing the applicability of PAMS to those NCore sites in larger CBSAs would still provide the desired improvement in geographic distribution while reducing the number of required sites down to a level that would provide sufficient resources to implement the state-directed EMP portion of the network. One commenter stated that they "supported a 1,000,000 population threshold because it would help prioritize resources to areas based on the greatest human health impacts." In addition, a number of commenters, while not commenting on the need for a population limit, did raise concerns about their ability to acquire and retain staff with the necessary expertise to collect PAMS measurements in less urbanized areas. As with the proposed network design, we recognize that the total number of sites and the ultimate spatial coverage under this option is also sensitive to changes in O3 concentrations. If current downward trends in O3 concentrations continue, many initially required sites would not be required soon after they were installed. As with the proposed option, this option could result in an unstable network resulting in an inefficient use of resources and inadequate spatial coverage to meet the network goals discussed above.
Upon further consideration and in response to the comments received, we are finalizing a network design that includes a requirement for states to make PAMS measurements at all NCore sites in CBSAs with a population of 1,000,000 people or more, irrespective of O3 attainment status. We believe this requirement will result in an appropriately sized network (roughly 40 sites) that will provide adequate spatial coverage to meet national model evaluation needs (Cavender, 2015). Redundancy is greatly reduced while important network coverage is added in the midwest, southeast, and mountain west. The improved spatial coverage will also strengthen the EPA's ability to track trends in precursor concentrations regionally.
Because the network requirement is not tied to attainment status, this final requirement will ensure network stability and allows for more efficient use of available resources. This final requirement also removes uncertainty as to applicability and aids planning and logistics involved with implementing the new requirements.  Monitoring agencies can determine the applicability of the fixed site requirements to their areas today, and begin to make plans for investments in equipment, shelter improvements, and staffing and training needs necessary to implement the fixed site requirements without having to wait for the designations process to be completed. In addition, this final requirement should alleviate concerns raised by monitoring agencies in more rural locations over the ability to attract and retain staff with the skills necessary to make PAMS measurements.
By adding the PAMS measurements to existing NCore sites, significant efficiencies can be obtained which should further reduce the costs of the fixed site network as NCore sites currently make many of the PAMS measurements.  Furthermore, adding the additional PAMS measurements (e.g., speciated VOCs, carbonyls, and mixing height) to existing NCore sites will improve our ability to assess other pollutants (e.g., air toxics and PM2.5).
Although, as discussed in comment and summarized above, we believe there are good reasons for not tying the requirement for fixed PAMS sites to O3 attainment status, we continue to believe that requiring PAMS measurements in areas that historically have had low O3 concentrations is unlikely to provide data of significant value to warrant the expense and effort of making such measurements. Therefore, we have included a provision that would allow a monitoring agency to obtain a waiver, based on Regional Administrator approval, in instances where CBSA-wide O3 design values are equal to or less than 85% of the 8-hour O3 NAAQS and where the site is not considered an important upwind or downwind site for other nonattainment areas. The EPA selected 85% as the threshold for this waiver provision as it has been used historically to identify locations needing additional monitoring for both the O3 and PM2.5 NAAQS. The EPA will work with the monitoring agencies and the Regions to help ensure consistent implementation of this waiver provision.
The second part of the proposed PAMS network design included monitoring agency directed enhanced O3 monitoring activities intended to provide data needed to understand an area's specific O3 issues. To implement this part of the PAMS network design, the EPA proposed to add a requirement for states with O3 nonattainment areas to develop an EMP. The purpose of the EMP was to improve monitoring for ambient concentrations of O3, NOx, total reactive nitrogen (NOy), VOC, and meteorology. The EPA suggested that types of activities that might be included in the state's EMP could include additional PAMS sites (e.g., upwind or downwind sites), additional O3 and NOx monitoring, ozonesondes or other aloft measurements, rural measurements, mobile PAMS sites, additional meteorological measurements, and episodic or intensive studies. The intent of the EMPs is to allow monitoring agencies flexibility in determining their specific data needs and collecting the information they need to understand their O3 problems.
We received comments on the proposed requirement for an EMP in states with O3 nonattainment areas. Most comments supported the requirement, but other comments raised a number of concerns. A number of commenters questioned the need for EMPs in marginal and moderate O3 nonattainment areas. They noted that in most cases, marginal O3 nonattainment areas were expected to come into compliance without state-specific controls. One commenter stated that "nonattainment areas projected to attain the standard without additional state-level actions may not need the PAMS resources and additional monitoring to develop a better understanding of their ozone issues." One commenter noted that "marginal ozone nonattainment areas are given only a few requirements because it is assumed that the areas will reach attainment within three years." Another commenter stated "requiring enhanced monitoring for any marginal or moderate area should only be implemented where such analyses show the need for this data." The EPA agrees that based on current trends in O3 concentrations and the EPA's own projections, states in marginal nonattainment areas likely will comply with the revised NAAQS without additional state-directed controls, and as such, an EMP is not necessary in marginal O3 attainment areas. Accordingly, the EPA is finalizing a requirement for EMPs in areas designated as moderate or above O3 nonattainment and, thereby, removing the applicability of the requirement for marginal areas. We believe this final requirement will provide the desired flexibility to allow states to identify enhanced monitoring needs while focusing resources for EMPs in areas of greater need of enhanced monitoring data.
Commenters expressed concerns over the lack of detail on what an approvable EMP would entail. As proposed, the EMPs would be reviewed and approved by the EPA Regional Administrator as part of the annual monitoring plan review process. One commenter recommended that "EPA detail the requirements of the EMPs for ozone nonattainment areas in future implementation guidance." One commenter stated that "EPA should provide some coordination between regional offices and technical guidance to state agencies that would be of assistance in developing and executing the EMPs." The requirements for the EMPs were intentionally left quite general in order to maximize the flexibility for states in identifying their specific data needs. Regional approval of the plans is required to ensure the enhanced monitoring planned will be commensurate with grant funds provided for EMPs. Nonetheless, the EPA understands the need for guidance on developing EMPs and commits to working with monitoring agencies and the regions to develop appropriate guidance on developing and reviewing EMPs.
2. Speciated VOC Measurements
Measurement of speciated VOCs important to O3 formation is a key aspect of the PAMS program. The existing PAMS requirements allow for a number of options in measuring speciated VOCs at PAMS sites which include 1) hourly measurements using an automatic gas chromatograph ("autoGC"), 2) eight 3-hour samples daily using canisters, or 3) one morning and one afternoon sample with a 3-hour or less averaging time daily using canisters plus continuous Total Non-methane Hydrocarbon (TNMHC) measurements.
The EPA believes that the current options provided for VOC measurement limit the comparative value of the data being collected, and proposed that required PAMS sites must measure and report hourly speciated VOCs, which effectively would require them to use an autoGC to measure VOCs in lieu of canisters. More complete and consistent speciated VOC data nationally would better help meet certain objectives of the PAMS program described above (e.g., a speciated ambient air database useful in evaluating control strategies, analyzing emissions inventory issues, corroborating progress toward attainment, and evaluating population exposure to air toxics). Furthermore, as noted by the CASAC AMMS, hourly VOC data are "particularly useful in evaluating air quality models and performing diagnostic emission attribution studies. These data can be provided on a near real-time basis and presented along with other precursor species (e.g., oxides of nitrogen and carbon monoxide) collected over similar averaging times." Longer time-averaged data are of significantly lower value for model evaluation. In addition, creating consistent monitoring requirements across the network would provide better data for analyzing regional trends and spatial patterns.
At the time the original PAMS requirements were promulgated, the canister options were included because the EPA recognized that the technologies necessary to measure hourly average speciated VOCs concentrations were relatively new and may not have been suitable for broad network use. At that time, GCs designed for laboratory use were equipped with auto-samplers designed to "trap" the VOC compounds from a gas sample, and then "purge" the compounds onto the GC column. The EPA did not believe that autoGCs were universally appropriate due to the technical skill and effort necessary at that time to properly operate an autoGC.
While the basic principles of autoGC technology have not changed, the hardware and software of modern autoGCs are greatly improved over that available at the time of the original PAMS requirements. Based on advice from the CASAC AMMS, the EPA initiated an evaluation of current autoGCs potentially suitable for use in the PAMS network. Based on the preliminary results, the EPA believes that typical site operators, with appropriate training, will have the skill necessary to operate a modern autoGC successfully. Considering the advances in autoGC technology, the added value obtained from hourly data, and the proposed move of PAMS measurements to NCore sites in O3 nonattainment areas, the EPA proposed to require hourly speciated VOC sampling at all PAMS sites. The EPA noted that this proposed requirement would effectively prevent the use of canisters to collect speciated VOCs at the required PAMS sites but that canister sampling may continue to be an appropriate method for collecting speciated VOCs at other locations as part of discretionary monitoring designed within the EMPs.
While the EPA believes that the proposed transition to hourly speciated VOC sampling is the appropriate strategy to take advantage of improved technology and to broaden the utility of collected data, we are also mindful of the additional rigidity that the proposed mandatory use of autoGCs may have for monitoring agencies, especially those that have experience with and have established effective and reliable canister sampling programs. Therefore, the EPA requested comment on the proposed requirement for hourly VOC sampling as well as the range of alternatives that might be appropriate in lieu of a strict requirement.
The EPA received a number of comments on the requirement to measure hourly VOCs at required PAMS sites. Many commenters agreed with requiring hourly VOC data. One commenter agreed that "hourly VOC data collection is the most appropriate and useful for PAMS monitors" and that "it is only appropriate to approve an alternative data collection interval if it is believed that the high ozone in an area is due to other pollutants, such as NOx or methane." One commenter stated they "supported the movement towards hourly PAMS VOC speciated measurements with flexibility to use canisters if programmatic or logistical needs indicate."
However, some commenters raised concerns with the hourly VOC requirement. Some commenters questioned if autoGCs would be capable of measuring important VOC species in their environment. One commenter noted that in their location (high desert) "the largest VOC present in our inventory is creosote, a compound not commonly measured with this instrumentation." One commenter stated that the "Southeastern United States is dominated by biogenic VOC emissions" and questioned "the benefits of an autoGC in understanding ozone formation in any potential nonattainment area in our State." Some questioned the detection capabilities of autoGCs as compared to canister sampling. One commenter found that the method detection limit (MDL) for their canister sampling was "consistently equal to or less than the autoGC instrumentation" based on the EPA's autoGC evaluation laboratory report (Cavender, October 3, 2014). Another commenter noted that the MDLs for many of the compounds and systems reported in the laboratory report were too high to be useful at PAMS sites. Another commenter stated that they found that "retention-time shifts made it difficult for instant identification of chemical peaks" and that "states should be allowed the flexibility to continue using canisters instead of autoGC."
As noted in the preamble, and the comments received, the EPA is currently completing an evaluation of commercially available autoGCs. A copy of the report for the laboratory phase of the study is available in the docket (RTI, 2014). As noted in the laboratory report, the MDL estimates made for the laboratory study were not conducted according to normal MDL testing procedures and as such the results should only be used to compare the various instruments being tested against each other. As part of the evaluation, the EPA identified the manufacturer's specifications for MDL. Most of the systems that are being evaluated have a manufacturer's estimated MDL in the range of 0.1 ppb to 0.5 ppb. Based on the evaluation of MDL capabilities and typical ambient concentrations of O3 precursors, the EPA believes that autoGCs are an appropriate method for gathering VOC data at most urban locations. However, canister sampling may be more appropriate in locations with low VOC concentrations.
 For the reasons discussed above and in the proposed rule, the EPA is finalizing a requirement for hourly speciated VOC measurements at required PAMS sites. The EPA believes that hourly VOC measurements will provide a more complete and consistent speciated VOC database to help meet the PAMS program objectives described above. Hourly VOC data are particularly useful in evaluating air quality models and performing diagnostic emission attribution studies. Longer time-averaged data are of lower value for model evaluation. Consistent monitoring requirements across the network will provide better data for analyzing regional trends and spatial patterns.
However, the EPA agrees that there may be locations where an autoGC may not be the most appropriate method for VOC measurement and that it is appropriate to allow for canister sampling in limited situations. Accordingly, the EPA is adding a waiver option (to be approved by the EPA Regional Administrator) to allow three 8-hour average samples every 3rd day as an alternative in cases where VOCs are not well measured by autoGC due to low concentrations of target compounds or where the predominant VOC compounds cannot be measured using autoGC technology (e.g., creosote in high desert environments). This alternative sampling frequency was selected to be consistent with the sampling frequency selected for carbonyls, which is discussed later in this preamble.
3. Carbonyl Measurements
Carbonyls include a number of compounds important to O3 formation that cannot currently be measured using the autoGCs or canisters used at PAMS sites to measure speciated VOCs. The current method for measuring carbonyls in the PAMS program is Compendium Method TO-11A (U.S. EPA, 1999). In this method, carbonyl compounds are adsorbed and converted into stable hydrazones using dinitrophenylhydrazine (DNPH) cartridges. These cartridges are then analyzed for the individual carbonyl compounds using liquid chromatography (LC) techniques. Three carbonyls are currently required to be measured in the PAMS program - formaldehyde, acetaldehyde, and acetone.
In 2006, the EPA revised the PAMS requirements such that carbonyl sampling was only required in areas classified as serious or above nonattainment for O3 under the 8-hour O3 standard which effectively reduced the applicability of carbonyl sampling to a few areas in California. This change was made in recognition that there were a number of issues with Method TO-11A that raised concerns with the uncertainty in the carbonyl data being collected. These issues include interferences (humidity and O3) and breakthrough (i.e., overloading of the DNPH cartridge) at high concentrations. While solutions for these issues have been investigated, these improvements have not been incorporated into Method TO-11A.
 A recent evaluation of the importance of VOCs and carbonyls to O3 formation determined that carbonyls, especially formaldehyde, are very important to O3 formation (Cavender, 2013). CASAC AMMS (U.S. EPA, 2011f) also noted the importance of carbonyls stating that "There are many compelling scientific reasons to measure carbonyls. They are a very important part of O3 chemistry almost everywhere." Although the EPA recognizes the issues that have been raised about the current method of measuring carbonyls, due to the importance of carbonyls to understanding O3 chemistry, the EPA proposed to require all required PAMS sites to measure carbonyls.
Several commenters agreed with the need for carbonyl data at PAMS sites. However, a number of commenters questioned the proposed frequency of eight 3-hour samples every day during the PAMS sampling season (June through August). Several commenters indicated that the frequency was too high. One commenter noted that the requirement would require 800 samples per season at each PAMS site and pointed out that this requirement, which was required at the inception of the PAMS program in the 1990s was "found to be prohibitively expensive, technically unsustainable, and qualitatively compromised." Another commenter stated that "this level of sampling would require a substantial amount of agency resources and seems unduly burdensome." A number of commenters also questioned the commercial availability of an 8-channel carbonyl sampler that would be needed to take eight 3-hour samples daily. In light of the comments and upon further review, the EPA agrees that the proposed frequency is unduly burdensome and is finalizing a requirement with a lower frequency.
A number of alternative frequencies were suggested in the comments. Several commenters suggested a frequency of three 8-hour samples on either a 1-in-6 day or 1-in-3 day basis. Another commenter suggested a frequency of eight 3-hour samples on a 1 in 6 day basis. The EPA notes that sampling on a 1-in-6 day frequency would lead to as little as 15 sampling days per PAMS sampling season. The EPA believes that 15 sampling days is too few to provide a meaningful representation of carbonyl concentrations over the PAMS sampling period. A sampling frequency of 1-in-3 days would lead to 30 sampling days per season with each day of the week being represented at least 4 times per sampling season. With regards to samples per day, a 3-hour sampling duration provides a better diurnal representation of carbonyl sampling compared with an 8-hour sampling duration; however 8-hour sampling can provide information useful for evaluating diurnal differences in carbonyl concentrations. Upon further consideration and in light of the comments received, the EPA is finalizing a carbonyl sampling requirement with a frequency of three 8-hour samples on a 1-in-3 day basis. This final requirement will result in approximately 90 samples per PAMS sampling season which the EPA believes is not unduly burdensome and will provide a reasonable representation of carbonyl concentrations.
A number of commenters noted the ongoing development of continuous formaldehyde instruments, and recommended that EPA allow for continuous formaldehyde measurements as an alternative to the manual cartridge based TO-11A method. The EPA agrees that continuous formaldehyde, with the ability to obtain hourly averaged measurements, would be a significantly more valuable that the longer averaged measurements. As a result, the EPA has added an option to allow for continuous formaldehyde as an alternative to the carbonyl measurements using TO-11A.
4. Nitrogen Oxides Measurements
 It is well known that NO and NO2 play important roles in O3 formation (U.S. EPA, 2013, Section 3.2.2). Under the current network design, Type 2 PAMS sites are required to measure NOx (which by definition is the sum of NO and NO2), and Types 1, 3, and 4 sites are required to measure NOy, which by definition includes NO, NO2, and other oxidized nitrogen compounds (NOz). NCore sites are currently required to measure NOy but are not required to measure NO2 separately.
In conventional NOx analyzers, NO2 is determined as the difference between the measured NO and NOx concentrations. However, due to the non-selective reduction of oxidized nitrogen compounds by the molybedenum converter used in conventional NOx monitors, the NO2 measurement made by conventional NOx monitors can be biased high due to the varying presence of NOz compounds that may be reported as NO2. The unknown bias from the NOz compounds is undesirable when attempting to understand O3 chemistry.
Improvements in reactive nitrogen measurements have been made since the original PAMS requirements were promulgated that allow for improved NO2 measurements. Selective photolytic converters have been developed that are not significantly biased by NOz compounds (Ryerson et al., 2000). Monitors using photolytic converters are commercially available and have been approved as FEMs for the measurement of NO2. In addition, methods that directly read NO2 have been developed that allow for very accurate readings of NO2 without some of the issues inherent to the "difference method" used in converter-based NOx analyzers. However, these direct reading NO2 analyzers generally do not provide an NO estimate, and would need to be paired with a converter-based NOx monitor or NOy monitor in order to also measure NO.
 As discussed above, the EPA is finalizing a PAMS network design such that PAMS measurements will be required at existing NCore sites in CBSAs with a population of 1,000,000 people or more. NCore sites currently are required to measure NO and NOy. NCore sites are not currently required to measure NO2. Due to the importance of accurate NO2 data to the understanding of O3 formation, the EPA proposed to require NO2 measurements at required PAMS sites. Since existing NCore sites currently measure NOy, either a direct reading NO2 analyzer or a photolytic-converter NOx analyzer could be used to meet the proposed requirement. The EPA believes conventional NOx analyzers would not be appropriate for making PAMS measurements due to the uncertainty caused by interferences from NOz compounds.
A number of commenters questioned the need for both NOy and NO2 measurements at PAMS sites. One commenter stated that "in dense urban areas an NO/NO2/NOx instrument may be adequate but in a more rural area an NO/NOy instrument may be preferable." Another commenter stated that due to the size of the grid cells used in grid models that "the impact of NOz interferences would be very small compared to other modeling uncertainties such as emission inventories and mixing heights." Another commenter suggested that "EPA should provide clear and specific guidance on how agencies can request that the NOy monitoring be eliminated from the NCore suite based on comparative data between the NO2 and NOy monitors."
The comments suggest that the model's ability to simulate the partitioning of reactive nitrogen is unimportant because there may be other errors in the model. The EPA believes that measurements should be routinely collected so that it can be demonstrated that the chemistry, meteorology, and emissions in the model are all of sufficient reliability for use in informing air quality management decisions. Monitoring sites rarely fall into simple categories of urban or rural, and the speciation of NOy varies considerably as a function of meteorology and time of day at a given site. The state-of-the-science in regulatory air quality modeling is such that accurate measurements of key O3 precursors must be available to demonstrate the credibility of the model predictions. The increased availability of special field study observations is leading to increased scrutiny of the chemical mechanisms used in regulatory modeling. Comprehensive and accurate measurement sites are needed to demonstrate the adequacy of the models and to respond to these challenges.
Measurements of NO, NO2, and NOy concentrations are critical to understanding atmospheric aging and photochemistry. These measurements will provide essential information about whether NOy compounds are fresh or aged which is important for understanding both local photochemistry (i.e. through indicator ratios to distinguish NOx vs VOC limited conditions) as well as for characterizing transport from upwind regions. These evaluations may be conducted using observations, box modeling or through complex photochemical grid based modeling. Accurate speciated and total NOy measurements are necessary for all three types of analysis. For these reasons, the EPA is finalizing the requirement for required PAMS sites to measure true NO2 in addition to NO and NOy.
5. Meteorology Measurements
The current PAMS requirements require monitoring agencies to collect surface meteorology at all required PAMS sites. As noted in the EPA's Technical Assistance Document (U.S. EPA, 1998) for the PAMS program, the PAMS requirements do not provide specific surface meteorological parameters to be monitored. As part of the implementation efforts for the original PAMS program, a list of recommended parameters was developed and incorporated into the TAD which includes wind direction, wind speed, temperature, humidity, atmospheric pressure, precipitation, solar radiation, and ultraviolet (UV) radiation. Currently, NCore sites are required to measure the above parameters with the exceptions of atmospheric pressure, precipitation, solar radiation, and UV radiation. In recognition of the importance of these additional measurements for understanding O3 formation, the EPA proposed to specify that required PAMS sites are required to collect wind direction, wind speed, temperature, humidity, atmospheric pressure, precipitation, solar radiation, and UV radiation. Since NCore sites are currently required to measure several of these surface meteorological parameters, the net impact of the proposal was to add the requirement for the monitoring of atmospheric pressure, precipitation, solar radiation, and UV radiation at affected NCore sites. The EPA received no significant comments on this portion of the proposal, and therefore is finalizing the requirement as proposed.
The existing PAMS requirements also require the collection of upper air meteorological measurements at one site in each PAMS area. The term upper air meteorological is not well defined in the existing PAMS requirements. As part of the implementation efforts for the original PAMS program, mixing height was added to the PAMS TAD as a recommended meteorological parameter to be monitored. Most monitoring agencies installed radar profilers to meet the requirement to collect upper air meteorology. Radar profilers provide data on wind and speed at multiple heights in the atmosphere. Radio acoustic sounding system (RASS) profilers are often included with radar profilers to obtain atmospheric temperature at multiple heights in the atmosphere and to estimate mixing height. The EPA recognizes that the upper air data on wind speed and wind direction from radar profilers can be very useful in O3 modeling. However, many of the current PAMS radar profilers are old and in need of replacement or expensive maintenance. In addition, the cost to install and operate radar profilers at all required PAMS sites would be prohibitive. Therefore, the EPA did not propose to add upper air wind speed and direction as required meteorological parameters to be monitored at required PAMS sites. Where monitoring agencies find the radar profiler data valuable, continued operation of existing radar profilers or the installation of new radar profilers would be appropriate to consider as part of the state's EMP.
As discussed above, mixing height is one upper air meteorological measurement that has historically been measured at PAMS sites. A number of methods can be used to measure mixing height in addition to radar profiler technology discussed above. Recent developments in ceilometer technology allow for the measurement of mixing height by changes in particulate concentrations at the top of the boundary layer (Eresmaa et al., 2006). Ceilometers provide the potential for continuous mixing height data at a fraction of the cost of radar profilers. Due to the importance of mixing height measurements for O3 modeling, the EPA proposed to add the requirement for monitoring agencies to measure mixing height at required PAMS sites.
A number of commenters questioned the need for mixing height measurements at PAMS sites. One commenter stated, "the photochemical modeling community has a long history of relying upon National Weather Service measurements for mixing height." Another commenter stated that "in some areas of the country the models used to predict mixing height are adequate, but in other mountainous or marine areas model-predicted mixing height data is inadequate." Accurate estimates of mixing height are important for appropriately characterizing concentrations of O3 and O3 precursors. Mixing height is also important for characterizing how modeled O3 may change as a result of changing NOx and VOC concentrations. For instance, if the modeled mixing height is too low causing unrealistically high concentration of NOx, then O3 destruction could be predicted when O3 production may be happening in the atmosphere. When this or the opposite situation exists in modeling it may lead O3 response to emissions changes that are less reliable for air quality planning purposes. While models are believed to do a reasonable job of predicting mixing height during the day, there is considerably more uncertainty in predicting this parameter during morning and evening transition periods and at night. Model O3 predictions are particularly sensitive to mixing height during the time periods for which uncertainty in this parameter is greatest.
Several commenters noted that nearby National Oceanic and Atmospheric Administration (NOAA) Automated Surface Observing System (ASOS) sites may be a better alternative for collection of mixing height data. As indicated in the proposal, the EPA is aware of the network of ceilometers operated by NOAA as part of ASOS. The EPA has been in discussions with NOAA regarding the potential for these systems to provide the needed mixing height data. However, the ASOS ceilometers are not currently equipped to provide mixing height data and NOAA has no current plans to measure mixing height in the future. Nonetheless, the EPA will continue to work with NOAA to determine if the ASOS ceilometers can be upgraded to meet the need for mixing height data, and included proposed regulatory language that will allow states a waiver to use nearby mixing height data from ASOS or other sources to meet the requirement to collect mixing height data at required PAMS sites when such data are suitable and available.
The EPA is finalizing the requirement for the measurement of mixing height at required PAMS sites due to the importance of mixing height in O3 modeling. A waiver option, to be approved by the Regional Administrator, is also being included to allow mixing height measurements to be obtained from other nearby sites (e.g., NOAA ASOS sites).
6. PAMS Season
Currently, PAMS measurements are required to be taken during the months of June, July, and August. This 3-month period is referred to as the "PAMS Season." As part of the PAMS re-evaluation, the EPA considered changes to the PAMS season. The 3-month PAMS season was originally selected to represent the most active period for O3 formation. However, the EPA notes that in many areas the highest O3 concentrations are observed outside of the PAMS season. As an example, the highest O3 concentrations in the mountain-west often occur during the winter months. Data collected during the current PAMS season would have limited value in understanding winter O3 episodes.
The CASAC AMMS (U.S. EPA, 2011f) noted in their report to the EPA that "it would be desirable to extend the PAMS monitoring season beyond the current June, July, August sampling period." But that "the monitoring season should not be mandated and rigid; it should be flexible and adopted and coordinated on a regional airshed basis." The EPA agrees with CASAC on the need for flexibility in determining when PAMS measurements should be taken to meet local monitoring needs but also agrees with CASAC that the flexibility "should not conflict with national goals for the PAMS program." A significant benefit of the standard PAMS season is that it ensures data availability from all PAMS sites for national- or regional-scale modeling efforts.
While EPA agrees with the potential benefit of extending the availability of PAMS measurements outside of the current season, we also considered the burden of requiring monitoring agencies to operate additional PAMS measurements (e.g., hourly speciated VOC) for periods that in some cases, might be much longer than the current 3-month season, for example, if the PAMS season was extended to match each state's required O3 monitoring season. Being mindful of the potential burden associated with a lengthening of the PAMS season as well as the potential benefits of the additional data, the EPA proposed to maintain the current 3-month PAMS monitoring season for required PAMS sites rather than extending the PAMS season to other periods where elevated O3 may be expected. No significant comments were received on the proposed PAMS season, and as such, for the reasons stated here and in the proposal, the EPA is not changing the 3-month PAMS season of June, July, and August.
The EPA believes that the 3-month PAMS season will provide a consistent data set of O3 and O3 precursor measurements for addressing the national PAMS objectives. Monitoring agencies are strongly encouraged to consider collecting PAMS measurements in additional periods beyond the required PAMS season as part of their EMP. The monitoring agencies should consider factors such as the periods of expected peak O3 concentrations and regional consistency when determining potential expansion of their specific monitoring periods beyond the required PAMS season.
7. Timing and Other Implementation Issues
The EPA recognizes that the changes to the PAMS requirements will require resources and a reasonable timeline in order to be successfully implemented. The PAMS program is funded, in part, as part of the EPA's section 105 grants. The EPA believes that the current national funding level of the PAMS program is sufficient to support these final changes, but changes in the distribution of PAMS funds will need to be made. The network design changes will require some monitoring agencies to start collection of new PAMS measurements, while other monitoring agencies will see reductions in PAMS measurement requirements. The EPA will work with the NAACA, AAPCA, and other monitoring agencies to develop an appropriate PAMS grant distribution strategy.
In addition to resources, the affected monitoring agencies will need time to implement the revised PAMS requirements. For the required PAMS sites, monitoring agencies can determine now which NCore sites will be required to make PAMS measurements based on readily available census data. However, monitoring agencies will still need time to evaluate and seek approval for alternative sites or alternative VOC methods. In addition, monitoring agencies will need time to make capital investments (primarily for the installation of autoGCs, NO2 monitors, and ceilometers), prepare appropriate QA documents, and develop the expertise needed to successfully collect PAMS measurements via training or otherwise. In order to ensure monitoring agencies have adequate time to plan and successfully implement the revised PAMS requirements, the EPA is requiring that monitoring agencies identify their plans to implement the PAMS measurements at NCore sites in their Annual Network Plan due July 1, 2018, and to begin making PAMS measurements at NCore sites by June 1, 2019. The EPA believes some monitoring agencies may be able to begin making PAMS measurements sooner than June 2019 and encourages early deployment where possible.
Monitoring agencies will need to wait until O3 designations are made to officially determine the applicability of the EMP requirement. The EPA proposed to allow two years after designations to develop EMPs, and that the EMPs would be submitted as part of their Annual Network Plan. Several commenters stated that due to the level of planning and coordination required for the EMPs, that the plans should instead be included as part of the 5-year network assessment. While the EPA agrees that the EMPs will require a substantial amount of planning and coordination, the next 5 year network assessment will not be due until July 1, 2020  -  nearly 5 years from the date of this final rulemaking. The EPA believes that it would be inappropriate to wait 5-years from the date of this rulemaking to develop plans for enhanced O3 monitoring. In addition, the EPA believes that the first round of EMP development should receive additional focus and review that may not be afforded as part of the larger network assessment. Finally, most monitoring agencies will be aware of their likely O3 attainment status well in advance of the official designations. In order to ensure timely development of the initial EMPs, the EPA is requiring affected monitoring agencies to submit their initial EMPs no later than two years following designations. However, subsequent review and revisions to the EMPs are to be made as part of the 5-year network assessments.
D. Addition of a New FRM for O3
The use of FRM analyzers for the collection of air monitoring data provides uniform, reproducible measurements of concentrations of criteria pollutants in ambient air. FRMs for various pollutants are described in several appendixes to 40 CFR part 50. For most gaseous criteria pollutants (including O3 in Appendix D of part 50), the FRM is described as a particular measurement principle and calibration procedure to be implemented, with further reference to specific analyzer performance requirements specified in 40 CFR part 53.
The EPA allows new or alternative monitoring technologies  -  identified as FEMs  -  to be used in lieu of FRMs, provided that such alternative methods produce measurements closely comparable to corresponding FRM measurements. Part 53 sets forth the specific performance requirements as well as the performance test procedures required by the EPA for determining and designating both FRM and FEM analyzers by brand and model.
To be used in a determination of compliance with the O3 NAAQS, ambient O3 monitoring data must be obtained using either a FRM or a FEM, as defined in parts 50 and 53. For O3, nearly all the monitoring methods currently used by state and local monitoring agencies are FEM (not FRM) continuous analyzers that utilize an alternative measurement principle based on quantitative measurement of the absorption of UV light by O3. This type of O3 analyzer was introduced into monitoring networks in the 1980s and has since become the predominant type of method used because of its all-optoelectronic design and its ease of installation and operation.
The existing O3 FRM specifies a measurement principle based on quantitative measurement of chemiluminescence from the reaction of ambient O3 with ethylene (ET-CL). Ozone analyzers based on this FRM principle were once widely deployed in monitoring networks, but now they are no longer used for routine O3 field monitoring because readily available UV-type FEMs are substantially less difficult to install and operate. In fact, the extent of the utilization of UV-type FEMs over FRMs for O3 monitoring is such that FRM analyzers have now become commercially unavailable. The last new commercial FRM analyzer was designated by the EPA in 1979. The current list of all approved FRMs and FEMs capable of providing ambient O3 data for use in NAAQS attainment decisions may be found on the EPA's website and in the docket for this action (U.S. EPA, 2014e). However, that list does not indicate whether or not each listed method is still commercially available.
1. Proposed Changes to the FRM for O3
Although the existing O3 FRM is still a technically sound methodology, the lack of commercially available FRM O3 analyzers severely impedes the use of FRM analyzers, which are needed for quality control purposes and as the standard to which candidate FEMs are required to be compared. Therefore, the EPA proposed to establish a new FRM measurement technique for O3 based on NO-chemiluminescence (NO-CL) methodology. This new chemiluminescence technique is very similar to the existing ET-CL methodology with respect to operating principle, so the EPA proposed to incorporate it into the existing O3 FRM as a variation of the existing ET-CL methodology, coupled with the same existing FRM calibration procedure.
A revised Appendix D to 40 CFR Part 50 was proposed to include both the original ET-CL methodology as well as the new NO-CL methodology, such that use of either measurement technique would be acceptable for implementation in commercial FRM analyzers. Currently, two O3 analyzer models (from the same manufacturer) employing the NO-CL methodology have been designated by the EPA as FEMs and would qualify for re-designation as FRMs under the revised O3 FRM. The rationale for selecting the new NO-CL FRM methodology, including what other methodologies were also considered, and additional information to support its selection are discussed in the preamble to the proposal for this action (79 FR 75366 - 75368). No substantive change was proposed to the existing O3 FRM calibration procedure, which would be applicable to both chemiluminescence FRM methodologies.
The proposed FRM in part 50, Appendix D also included numerous editorial changes to provide clarification of some provisions, some revised wording, additional details, and a more refined numbering system and format consistent with that of two other recently revised FRMs (for SO2 and CO).
As noted in the proposal, there is substantial similarity between the new and previously existing FRM measurement techniques, and comparative field data show excellent agreement between ambient O3 measurements made with the two techniques (U.S. EPA 2014f). Therefore, the EPA believes that there will be no significant impact on the comparability between existing ambient O3 monitoring data based on the original ET-CL methodology and new monitoring data that may be based on the NO-CL methodology.
The proposed FRM retains the original ET-CL methodology, so all existing FEMs, which were designated under part 53 based on demonstrated comparability to that ET-CL methodology, will retain their FEM designations. Thus, there will be no negative consequences or disruption to monitoring agencies, which will not be required to make any changes to their O3 monitors due to the revised O3 FRM. New FEMs would be designated under part 53, based on demonstrated acceptable comparability to either FRM methodology.
2. Comments on the FRM for O3
Comments that were received from the public on the proposed new O3 FRM technique are addressed in this section. Most commenters expressed general support for the proposed changes, although a few commenters expressed some concerns. The most significant issue discussed in comments was the relatively small but nevertheless potentially significant interference of water vapor observed in the ET-CL technique. As some comments pointed out, this interference is positive and could possibly affect NAAQS attainment decisions. The available NO-CL FEM analyzers include a sample dryer, which minimizes this interference.  As noted previously, very few, if any, ET-CL FRM analyzers are still in operation. The ET-CL (with and without a sample dryer), the proposed NO-CL FRM, and all designated FEM analyzers have demonstrated compliance with the substantially reduced water vapor interference equivalent limit specified in 40 CFR part 53.
The proposed FRM mentioned the need for a sample air dryer for both ET-CL and NO-CL FRM analyzers. In response to these comments, the wording of the ET-CL FRM has been augmented to clarify the requirement for a dryer in all newly designated FRMs (the only change being made by the EPA to the existing ET-CL FRM as proposed). Also, the interference equivalent limit for water vapor in part 53 was proposed to be substantially reduced from the current 0.02 ppm to 0.002 ppm. The interference equivalent test for water vapor applicable to the new NO-CL candidate FRM analyzers (specified in Table B-3 of part 53) was proposed to be more stringent than the corresponding existing test for ET-CL FRM analyzers by requiring that water vapor be mixed with O3. This mixing requirement was not part of the existing test for ET-CL candidate analyzers (denoted by footnote 3 in Table B-3). However, in further response to these commenters' concerns, the EPA has modified Table B-3 to extend this water vapor mixing requirement to newly designated ET-CL analyzers, as well. These measures should insure that potential water vapor interference is minimized in all newly designated FRM analyzers.
Several comments indicated concern that currently-designated FEM analyzers retain their designation without retesting if the new FRM were promulgated. The current ET-CL FRM is being retained; therefore, it is not necessary to make these new requirements retroactive to existing designated FEM analyzers. The existing FEM analyzers will not be required to be retested, and their FEM designation will be retained so that there will be no disruption to current monitoring networks.
Although beyond the scope of this rulemaking, other comments concerned potential hazards of the NO compressed gas supply required for NO-CL analyzer operation, and the current non-availability of a photolytic converter to provide an alternative source of NO from a less hazardous nitrous oxide gas supply. With regard to the photolytic converter, the EPA would approve such a converter as a source of NO if requested by an FRM analyzer manufacturer, upon demonstration of adequate functionality.
A few commenters liked the "scrubberless UV absorption" (SL-UV) measurement technique. The EPA has identified the SL-UV method as a potentially advantageous candidate for the O3 FRM, but could not propose adopting it until additional test and performance information becomes available. A related comment requested clarification that promulgation of the proposed revised FRM would not preclude future consideration of other O3 measurement techniques such as SL-UV. In response, the EPA can always consider new technologies for FRMs under 40 CFR 53.16 (Supersession of reference methods). However, a revised or amended FRM that included the SL-UV technique, as set forth in Appendix D of 40 CFR Part 50, would have to be promulgated as part of a future rulemaking, before a SL-UV analyzer could be approved as an FRM under 40 CFR Part 53.
One comment suggested that the value for the absorption cross section of O3 at 254 nm used by the FRM's calibration procedure should be changed. The comment indicated that the nearly 2% difference effectively lowers the O3 NAAQS by that amount. Using the corrected value would resolve much of the difference observed between O3 measurements calibrated against the UV standard reference photometer versus those calibrated using NO gas phase titration and it would allow the EPA to adopt the less complex and more economical Gas Phase Titration (GPT) technique as the primary calibration standard for the FRM. The EPA will await the results of further studies determining the value of the O3 cross section at 254 nm before making a change to the calibration procedures and will not finalize changes to the calibration procedures in this final rule.
E. Revisions to the Analyzer Performance Requirements
1. Proposed Changes to the Analyzer Performance Requirements
In close association with the proposed O3 FRM, the EPA also proposed changes to the associated analyzer performance requirements for designation of FRMs and FEMs for O3, as set forth in 40 CFR part 53. These changes were largely confined to Table B-1, which specifies performance requirements for FRM and FEM analyzers for SO2, CO, O3, and NO2, and to Table B-3, which specifies test concentrations for the various interfering agent (interferent) tests. Minor changes were also proposed for Figure B-5 and the general provisions in subpart A of part 53. All of these proposed changes are described and discussed more fully in the preamble to the proposal for this action (79 FR 75368 - 75369).
Modest changes proposed for Table B-3 would add new interferent test concentrations specifically for NO-CL O3 analyzers, which include a test for NO2 interference.
Several changes to Table B-1 were proposed. Updated performance requirements for "standard range" analyzers were proposed to be more consistent with current O3 analyzer performance capabilities, including reduced limits for noise allowance, lower detectable limit (LDL), interference equivalent, zero drift, span drift, and lag, rise, and fall times. The previous limit on the total of all interferents was proposed to be withdrawn as unnecessary and to be consistent with that same change made previously for SO2 and CO analyzers. Also, the span drift limit at 20% of the upper range limit (URL) was proposed to be withdrawn because it has similarly been shown to be unnecessary and to maintain consistency with that same change made previously for SO2 and CO analyzers.
The form of the precision limits at both 20% and 80% of the URL was proposed to be changed from ppm to percent. The proposed new limits (in percent) were set to be equivalent to the previously existing limits (in ppm) and thus remain effectively unchanged. This change in form of the precision limits in Table B-1 has been previously made for SO2 and CO analyzers, and was proposed to extend also to analyzers for NO2, (again with equivalent limits) for consistency and to simplify Table B-1 across all types of analyzers to which the table applies. A new footnote proposed for Table B-1 clarifies the new form for precision limits as "standard deviation expressed as percent of the URL." Also proposed was a revision to Figure B-5 (Calculation of Zero Drift, Span Drift, and Precision) to reflect the changes proposed in the form of the precision limits and the withdrawal of the limits for total interference equivalent.
Concurrent with the proposed changes to the performance requirements for candidate O3 analyzers, the EPA conducted a review of all designated FRM and FEM O3 analyzers currently in production or being used, and verified that all meet the proposed new performance requirements. Therefore, none would require withdrawal or cancellation of their current FRM or FEM respective designations.
Finally, the EPA proposed new, optional, "lower range" performance limits for O3 analyzers operating on measurement ranges lower (i.e., more sensitive) than the standard range specified in Table B-1. The new performance requirements are listed in a new "lower range" column in Table B-1 and will provide for more stringent performance in applications where more sensitive O3 measurements are needed.
Two minor changes were proposed to the general, administrative provisions in Subpart A of part 53. These include an increase in the time allowed for the EPA to process requests for approval of modifications to previously designated FRMs and FEMs and the withdrawal of a requirement for annual submission of Product Manufacturing Checklists associated with FRMs and FEMs for PM2.5 and PM10-2.5. No comments were received on these proposed changes and the EPA will be finalizing these revisions in this rulemaking.
2. Comments on the Analyzer Performance Requirements
Several comments were received related to the proposed changes to the analyzer performance requirements of part 53, and most were supportive. Comments from a few monitoring agencies suggested that the more stringent performance requirements proposed might be difficult to achieve or would increase monitor maintenance and cost. The EPA is also clarifying that these requirements apply only to the performance qualification requirements for designations of new FRM and FEM analyzers and will have no impact on a monitoring agency's operation of existing O3 analyzers.
More specific comments from an analyzer manufacturer pointed out that the proposed lower limits for noise and LDL may be too stringent, the former because low-cost portable analyzers may have shorter absorption cells, and the latter because of limitations of current calibration technology. After further consideration of available analyzer performance data in light of these comments, the EPA agrees and is changing the noise limits from the proposed values of 1 ppb and 0.5 ppb (for the standard and lower ranges, respectively) to 2.5 ppb and 1 ppb (respectively). The EPA is also changing the LDL limit from the proposed values of 3 ppb and 1 ppb (respectively) to 5 ppb and 2 ppb (respectively). These new limits are still considerably more stringent than the previous limits (for the standard range) and are also consistent with those recommended by the commenter and the current performance capabilities of existing analyzer/calibration technology.
This commenter also pointed out that the proposed lower limit for 12-hour zero drift, together with the way the prescribed test is carried out, resulted in the test being dominated by analyzer noise rather than drift. The EPA agrees with this comment in general but believes that further study is needed before any specific changes can be proposed for the 12-hour zero drift test, particularly since any such changes would affect analyzers for other gaseous pollutants, as well.
Other comments suggested that there was no need for the proposed new, low-range performance requirements, because of cost and that available calibrators would be inadequate for calibration of such low ranges. The EPA disagrees with these comments and believes, as noted in the proposal preamble, that there is a definite need for low-level O3 measurements in some applications and that suitable calibration for such low-level measurement ranges can be adequately carried out. As stated previously, the new "low range" specifications for O3 analyzers are optional.
Several comments pointed out some typographical errors related to footnotes in Table B-3, as proposed; these errors have been corrected in the version of Table B-3 being finalized today.
EPA is finalizing the proposed amendments to both the O3 FRM in Appendix D of part 50 and provisions in part 53, modified as described above, in response to the comments received.
VII. Grandfathering Provision for Certain PSD Permits
A. Summary of the Proposed Grandfathering Provision
      The EPA proposed a transition plan that would apply to Prevention of Significant Deterioration (PSD) applications that have been submitted to the reviewing authority and meet certain milestones in the review process prior to specific trigger dates, i.e., the signature date or effective date of the revised O3 NAAQS. Absent a regulatory grandfathering provision, the EPA interprets section 165(a)(3)(B) of the CAA and the implementing PSD regulations at 40 CFR 52.21(k)(1) and 51.166(k)(1) to require that PSD permit applications must include a demonstration that emissions from the proposed facility will not cause or contribute to a violation of any NAAQS that is in effect as of the date the PSD permit is issued. The proposal described a grandfathering provision that would enable eligible PSD applications to make the demonstration that the proposed project would not cause or contribute to a violation of any NAAQS with respect to the NAAQS in effect at the time the relevant permitting benchmark for grandfathering was reached, rather than the revised O3 NAAQS. We proposed that the grandfathering provision would apply specifically to either of two categories of pending PSD permit applications: (1) applications for which the reviewing authority has formally determined that the application is complete on or before the signature date of the final rule revising the O3 NAAQS; and (2) applications for which the reviewing authority has first published a public notice of the draft permit or preliminary determination before the effective date of the revised NAAQS.
      In the proposal, we also noted that for sources subject to the federal PSD program under 40 CFR 52.21, the EPA and air agencies that have been delegated authority to implement the federal PSD program for the EPA would apply the grandfathering provision to any source whose PSD application status satisfies either of the two criteria that make the application eligible for grandfathering. Accordingly, if a particular source does not qualify under the first criterion based on a complete application determination, it may qualify under the second criterion based on the public notice announcing the draft permit or preliminary determination. Conversely, a source may qualify for grandfathering under the first criterion, even if it does not satisfy the second.
      The EPA also proposed revisions to the PSD regulations at 40 CFR 51.166 that air agencies that issue PSD permits under a SIP-approved PSD permit program should have discretion to adopt provisions into the SIP that allow for grandfathering of pending PSD permits under the same circumstances as set forth in the federal PSD regulations. With regard to implementing the grandfathering provision, we also explained that air agencies with the EPA-approved PSD programs in their SIPs would have additional flexibility for implementing the proposed grandfathering provision to the extent that any alternative approach is at least as stringent as the federal provision. In addition, the proposal recognized that some air agencies do not make formal completeness determinations; thus, only the latter criterion based on the issuance of a public notice would be relevant in such cases and the state could elect to adopt only that criterion into its SIP. Accordingly, the EPA proposed to add a grandfathering provision to 40 CFR 51.166 containing the same two criteria as proposed for 40 CFR 52.21.
B. Comments and Responses
      Many of the comments supported the concept of grandfathering. Some of these comments, mostly by state and local air agencies, supported the grandfathering provision as proposed. Many others recommended alternative approaches to grandfathering based on several different trigger dates. Several comments recommended that air agencies should be allowed to grandfather certain PSD permit applications and issue a PSD permit based on the 2008 O3 NAAQS after the area is designated nonattainment for the revised O3 NAAQS. An opposing set of comments, representing a coalition of eight environmental groups and one health advocacy group, strongly objected to the proposal, claiming that the EPA did not have any authority under the CAA to exempt or grandfather permit applicants from the statutory PSD permitting requirements. We are addressing some of these comments below and others in the Response to Comment Document that is included in the rule docket.
      Comments that recommended broadening the scope of the proposed grandfathering provision suggested a variety of approaches. Some air agency and industry comments recommended that the EPA adopt a grandfathering provision applicable only to those PSD applications for which the reviewing authority has determined the application to be complete on or before the signature date of the revised NAAQS. Other air agency and industry comments recommended that grandfathered status be determined only on the basis of whether the relevant permitting milestone has been achieved by the effective date of the revised NAAQS.
      Several other comments recommended that the EPA grandfather all PSD applications for which a final PSD permit will be issued prior to the effective date of the area designations for the revised NAAQS. One of these comments explained that without some transition provisions in the final rule, it may be impossible for a source to demonstrate attainment if the current ambient air monitoring data indicates a revised, lowered standard is not being met. One of these comments suggested that the extended period for grandfathering a source from the revised NAAQS would provide states with additional time to establish offset banks or similar systems for new nonattainment areas.
      Other comments recommended that air agencies be allowed to grandfather either all or certain PSD permit applications received before the effective date of the final nonattainment designations for the revised O3 NAAQS. These comments supported allowing air agencies to issue PSD permits to grandfathered sources even after the area in which the source proposes to locate is designated nonattainment for the revised O3 NAAQS. One comment saw this as being necessary because the development of the regulatory framework that will support the revised NAAQS, such as development of a credit market or even a transition into Nonattainment New Source Review (NNSR) permitting, does not instantaneously accompany the revised standard. Hence, the comment added that "[d]uring the Interim Period (the time between revision of the NAAQS rule and development of the regulatory framework) the project may be unable to secure offsets and no offsets would be available for purchase". Another comment explained that the extended period for grandfathering sources from the revised O3 NAAQS was needed to "minimize disruption to complex projects that may have been under development since before the EPA published the proposed NAAQS revision." This comment noted the "PSD projects commonly undergo years of engineering and other development resources before an air permit application can be prepared."
      The EPA does not agree with the set of comments recommending the use of a grandfathering approach that would rely on milestones linked to a trigger date occurring after the effective date of the revised O3 NAAQS. The EPA does not believe it is appropriate from a policy perspective to unreasonably or unnecessarily delay implementation of these revised standards under the PSD program. As explained in more detail below, the purpose of the grandfathering provision is to provide a reasonable transition mechanism for certain PSD applications and the EPA believes that the milestones proposed and finalized here strike the appropriate balance in providing for such a reasonable transition. Moreover, in some cases, some of these recommended approaches could enable a situation where a PSD permit would be issued to a source during a future period when the area is designated nonattainment for the revised O3 NAAQS. As explained below, the EPA does not believe that this specific outcome is permissible under the CAA.
      The EPA does not agree with the comments suggesting that the grandfathering provision should be expanded to apply to any PSD application received before the effective date of the final nonattainment designations for the revised O3 NAAQS.  Because the process for reviewing PSD permit applications and issuing a final PSD permit is time consuming, such an approach could allow issuance of PSD permits to grandfathered sources even after the area in which the source proposes to locate is designated nonattainment for the revised O3 NAAQS.  The EPA does not agree that grandfathering should be extended in a way that would allow a source located in an area designated as nonattainment for a pollutant at the time of permit issuance to obtain a PSD permit for that pollutant rather than a NNSR permit. The EPA does not interpret the CAA or its implementing regulations to allow such an outcome. Specifically, CAA section 172(c)(5) requires that permits issued to new or modified stationary sources "anywhere in the nonattainment area" meet the requirements of CAA section 173, which contains the NNSR permit requirements. In addition, the PSD implementing regulations at 40 CFR 52.21(i)(2) contain an exemption that provides that the substantive PSD requirements shall not apply to a pollutant if the owner or operator demonstrates that the facility is located in an area designated nonattainment for that pollutant under CAA section 107 of the Act. See also 40 CFR 51.166(i)(2) (allowing for the same exemption in SIP-approved PSD permitting programs).  Moreover, given the adverse air quality conditions that already exist in a nonattainment area and the congressional directive to reach attainment as expeditiously as practicable, construction of a major stationary source that significantly increases emissions in such an area should be expected to address all of the NNSR requirements, which are designed to ensure that a new or modified major stationary source will not interfere with reasonable progress toward attainment, even if this could cause delay to the permit applicant.
      With respect to the comments that suggested the effective date of the NAAQS should be used as the trigger date for both milestones, the EPA does not agree that such a change is necessary.  The EPA believes that the purpose of the grandfathering provision is to provide a reasonable transition mechanism for PSD applications for which both the applicant and the reviewing authority have committed substantial resources and in situations where the need to satisfy the demonstration requirement under CAA section 165(a)(3) could impact the reviewing authority's ability to meet the statutory deadline for issuing a permit within one year of the completeness determination. In situations where the reviewing authority has not yet issued a completeness determination as of the signature date of the revised O3 NAAQS, both the permit applicant and the reviewing authority have sufficient notice of the revised standard so that it can be addressed before the completeness determination is issued and the one-year clock begins to run. The grandfathering provision issued in this rulemaking is crafted to draw a reasonable balance that accommodates the requirements under both CAA sections 165(a)(3) and 165(c). Any modification of the trigger dates further than is necessary to accommodate these concerns could upset this balance.
      With respect to the comments that suggested adopting a grandfathering provision applicable only to those PSD applications for which the reviewing authority has determined the application to be complete on or before the signature date of the revised NAAQS, the EPA is not making this change because we understand that not all reviewing authorities issue formal completeness determinations.  Including a grandfathering provision based on the publication of a public notice of the draft permit or preliminary determination provides a reasonable transition mechanism for PSD applications in situations where the reviewing authority does not issue formal completeness determinations, but the applicant and the reviewing authority have both committed substantial resources to the pending permit application at the time the NAAQS takes effect.
      An opposing set of comments -- submitted by a consortium of eight environmental groups and one health advocacy group -- challenged the proposed grandfathering provision on the basis that the EPA did not have the legal authority to grandfather sources from PSD requirements and that the plain language of CAA section 165 forecloses the EPA's proposed approach as well as several other legal considerations. The EPA respectfully disagrees with these comments, including with the interpretations of the CAA that they offer.  As explained in the proposal, in other actions, and in the Response to Comment Document in the docket, and as summarized in the rationale for the final action presented below in VII.C, the EPA believes that the CAA provides it authority and discretion to establish a PSD grandfathering provision such as the one being adopted today through a rulemaking process. The EPA is providing a further, detailed analysis fully responding to this set of comments, as well as other comments related to the grandfathering provision, in the Response to Comment Document in the docket.
C. Final Action and Rationale
      After consideration and evaluation of all the public comments received on the grandfathering provision, the EPA is finalizing this provision as proposed.  This final rule includes the same rule language for the grandfathering provision as previously proposed for the PSD regulations at 40 CFR 52.21(i)(12) and 51.166(i)(11), respectively. The provision as contained in the final rule continues to focus on the two proposed milestones and corresponding trigger dates, linking the complete application determination to the signature date of the final NAAQS rule, and the draft permit or preliminary determination to the effective date of this rule. Thus, under the grandfathering provision as finalized, two categories of pending PSD permit applications would be eligible for grandfathering: (1) applications for which the reviewing authority has formally determined that the application is complete before the signature date of the revised O3 NAAQS, or (2) applications for which the reviewing authority has first published a notice of a draft permit or preliminary determination before the effective date of the revised O3 NAAQS. The EPA believes that it continues to be appropriate to include the two proposed milestones for pending permit applications to be eligible for  grandfathering because, while a completeness determination is often the first applicable, some air agencies do not determine applications complete as part of their permit process.
      Where the EPA is the reviewing authority, the EPA intends to apply the grandfathering provision to PSD applicants pursuant to PSD regulations at 40 CFR 52.21 primarily through the use of the completeness determination milestone because the EPA Regional Offices make a formal completeness determination for any PSD application that they receive and review. The EPA is including the second criterion in 40 CFR 52.21 so that if any air agency that reviews PSD applications pursuant to 40 CFR 52.21 under a delegation agreement does not make formal completeness determinations as part of its permit review process, pending applications can still qualify for grandfathering under the second criterion. Hence, under 40 CFR 52.21, a permit application may qualify for grandfathering under either of the two sets of milestones and trigger dates contained in the provision.
      The EPA is also amending the PSD regulations at 40 CFR 51.166 to provide a comparable grandfathering provision for states and other air agencies that issue PSD permits under SIP-approved PSD programs. Nevertheless, such air agencies have discretion to not grandfather PSD applications or to apply grandfathering in another manner as long as it is at least as stringent as the provision being added to 40 CFR 51.166. Accordingly, an air agency may elect to rely on both sets of milestones and trigger dates or it may grandfather on the sole basis of only one set. However, the EPA anticipates that once a decision is made concerning the use of either set of milestones and trigger dates, the air agency will apply grandfathering consistently to all pending PSD permit applications.
      As explained in more detail in the proposal, absent a regulatory grandfathering provision, the EPA interprets section 165(a)(3)(B) of the CAA and the implementing PSD regulations at 40 CFR 52.21(k)(1) and 51.166(k)(1) to require that PSD permit applications must include a demonstration that emissions from the proposed facility will not cause or contribute to a violation of any NAAQS that is in effect as of the date the PSD permit is issued. However, reading CAA section 165(a)(3)(B) in context with other provisions of the Act and the legislative history, the EPA interprets the Act to provide it authority to establish grandfathering provisions through regulation. The EPA has explained its interpretation of its authority to promulgate grandfathering provisions in previous rulemaking actions, most recently in the establishing the regulatory grandfathering provision for the 2013 PM2.5 NAAQS, 78 FR 3086, 3254-56 (January 15, 2013), as well as in the proposal for this action. The EPA is providing a fuller discussion of this authority in the Response to Comment Document for this action.
      To summarize briefly, the addition of this grandfathering provision is permissible under the discretion provided by the CAA for the EPA to craft a reasonable implementation regulation that balances competing objectives of the statutory PSD program found in CAA sections 165(a) (which requires a permit applicant to demonstrate that its proposed project will not cause or contribute to a violation of any NAAQS) and 165(c) (which requires that a PSD permit be granted or denied within one year after the permitting authority determines the application for such permit to be complete), in light of the statutory ambiguity that arises concerning how the requirements under CAA section 165(a)(3)(B) should be applied to a limited set of pending PSD permit applications when the O3 NAAQS is revised. Section 109(d)(1) of the CAA requires the EPA to review existing NAAQS and make appropriate revisions every five years.  Section 165(a)(3)(B) of the CAA requires that a permit applicant demonstrate that its proposed project will not cause or contribute to a violation of any NAAQS. At the same time, section 165(c) of the CAA requires that a PSD permit be granted or denied within 1 year after the permitting authority determines the application for such permit to be complete. The Act does not clearly address how the requirements of CAA section 165(a)(3)(B) should be met for PSD permit applications that are pending when the NAAQS are revised, nor does it address how the requirements of sections 165(a)(3) and 165(c) of the CAA should be balanced in light of the statutory requirement to review the NAAQS every five years.  As Congress has not spoken precisely to this issue, the EPA has the discretion to apply a permissible interpretation of the Act that balances the statutory requirements to make a decision on a permit application within one year and to ensure the new and modified sources will only be authorized to construct after showing they can meet the substantive permitting criteria. Chevron, U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 843-44 (1984).
      In addressing these gaps in the Act and the tension that exists in section 165, the EPA also turns to CAA section 301, where the Administrator is authorized "to prescribe such regulations as are necessary to carry out his functions under this chapter." Sections 165(a)(3) and 165(c) of the CAA make clear that the interests behind CAA section 165 include both protection of air quality and timely decision-making on pending permit applications.  The legislative history illustrates congressional intent to avoid delays in permit processing. S. Rep. No. 94 - 717, at 26 (1976) ("nothing could be more detrimental to the intent of this section and the integrity of this Act than to have the process encumbered by bureaucratic delay").  Thus, when read in combination, these provisions of the CAA provide the EPA with the discretion to issue regulations to grandfather pending permit applications from having to address a revised NAAQS where necessary to achieve both CAA objectives  -  to protect the NAAQS and to avoid delays in processing PSD permit applications. Accordingly, the EPA is seeking in this action to balance the requirements in the Act to make a decision on a permit application within one year and to ensure that new and modified sources will only be authorized to construct after showing they can meet the substantive permitting criteria that apply to them.  The EPA is achieving this balance by determining through rulemaking which O3 NAAQS apply to certain permit applications that are pending when the revised O3 NAAQS takes effect for purposes of satisfying the requirements under section 165(a)(3)(B) and in doing so, it is determining, in effect, when the revised O3 NAAQS becomes operative for certain permit applications for purposes of the requirement that the source demonstrate that its emissions do not cause or contribute to a violation of the NAAQS.
      This approach is consistent with a recent opinion the U.S. Court of Appeals for the Ninth Circuit, which recognized the EPA's traditional exercise of grandfathering authority through rulemaking and indicated that this approach was consistent with the statutory requirement to "enforce whatever regulations are in effect at the time the agency makes a final decision" because it involved identifying "an operative date, incident to setting the new substantive standard, and the grandfathering of pending permit applications was explicitly built into the new regulations." Sierra Club v. EPA, 762 F.3d 971, 983 (9th Cir. 2014). As discussed in more detail in the EPA's Response to Comment Document, the EPA believes that this case supports the EPA's action in this rulemaking. In fact, the court favorably discussed prior adoption of regulatory grandfathering provisions that are similar to the action in this rulemaking, such as the grandfathering provision that the EPA promulgated when revising the PM2.5 NAAQS that became effective in 2013.  See id. at 982-83.
      This action is also consistent with previous actions in which the EPA has previously recognized that the CAA provides discretion for the EPA to establish grandfathering provisions through regulations such that certain PSD permit applications are grandfathered from requirements that would otherwise become applicable to the application while the application is pending. Examples of previous references to the EPA's authority to grandfather certain applications through rulemaking include 45 FR 52683, August 7, 1980; 52 FR 24672, July 1, 1987; U.S. EPA, 2011c, pp. 54 to 61; and most recently 78 FR 3086, January 15, 2013.
This grandfathering provision does not apply to any applicable PSD requirements related to O3 other than the requirement to demonstrate that the proposed source does not cause or contribute to a violation of the revised O3 NAAQS. Sources with projects qualifying under the grandfathering provision will be required to meet all the other applicable PSD requirements, including applying BACT to all applicable pollutants, demonstrating that emissions from the proposed facility will not cause or contribute to a violation of the O3 NAAQS that was in effect at the time the relevant grandfathering milestone was satisfied, and addressing any Class I area and additional O3-related impacts in accordance with the applicable PSD requirements.  In addition, this grandfathering provision would not apply to any permit application for a new or modified major stationary source of O3 located in an area where NNSR requirements apply to the source at the time of permit issuance.
VIII. Implementation of the Revised O3 Standards
This section provides background information for understanding the implications of the revised O3 NAAQS and describes the EPA's plans for providing revised rules or additional guidance on some subjects in a timely manner to assist states with their implementation efforts under the requirements of the CAA. This section also describes existing EPA interpretations of CAA requirements and other EPA guidance relevant to implementation of revised O3 NAAQS. Relevant CAA provisions that provide potential flexibility with regard to meeting implementation timelines are highlighted and discussed.
This section also contains a discussion of how existing requirements to reduce the impact on O3 concentrations from the stationary source construction in permit programs under the CAA are affected by the revisions to the O3 NAAQS. These are the PSD and Nonattainment New Source Review (NNSR) programs. As discussed in section VII of this preamble, to facilitate a smooth transition to the PSD requirements for the revised O3 NAAQS, the EPA is finalizing as part of this rulemaking a grandfathering provision that applies to certain PSD permit applications that are pending and have met certain milestones in the permitting process when the revised O3 NAAQS is signed or becomes effective, depending on the milestone.
A. NAAQS Implementation Plans
1. Cooperative Federalism
As directed by the CAA, reducing pollution to meet national air quality standards always has been a shared task, one involving the federal government, states, tribes and local air quality management agencies. The EPA develops regulations and strategies to reduce pollution on a broad scale, while states and tribes are responsible for implementation planning and any additional emission reduction measures necessary to bring specific areas into attainment. The agency supports implementation planning with technical resources, guidance, and program rules where necessary, while air quality management agencies use their knowledge of local needs and opportunities in designing emission reduction strategies that will work best for their industries and communities.
This partnership has proved effective since the EPA first issued O3 standards more than three decades ago. For example, 101 areas were designated as nonattainment for the 1-hour O3 standards issued in 1979. As of the end of 2014, air quality in all but one of those areas meets the 1-hour standards. The EPA strengthened the O3 standards in 1997, shifting to an 8-hour standard to improve public health protection, particularly for children, the elderly, and other sensitive individuals. The 1997 standards drew significant public attention when they were proposed, with numerous parties voicing concerns about states' ability to comply. However, after close collaboration between the EPA, states, tribes and local governments to reduce O3-forming pollutants, significant progress has been made. Air quality in 108 of the original 115 areas designated as nonattainment for the 1997 O3 NAAQS now meets that standard. Air quality in 18 of the original 46 areas designated as nonattainment for the 2008 O3 NAAQS now meets that standard.
The revisions to the primary and secondary O3 NAAQS discussed in sections II.E and IV.G of this preamble trigger a process under which states first review capacity and authorities to ensure the CAA requirements associated with the new standards can be carried out, and make recommendations to the Administrator regarding area designations. Then, the EPA promulgates the final area designations. States also are required to review, modify, and supplement their existing SIPs. The O3 NAAQS revisions also apply to the transportation conformity and general conformity determinations, and affect which preconstruction permitting requirements apply to sources of O3 precursor emissions, and the nature of those requirements.
The EPA has regulations in place addressing the general requirements for SIPs, and there are also provisions in these existing rules that cover O3 SIPs (40 CFR part 51). States likewise have provisions in their existing SIPs to address air quality for O3 and to implement the existing O3 NAAQS. In the course of the past 45 years of regulating criteria pollutants, including O3, the EPA has also provided general guidance on the development of SIPs and administration of construction permitting programs, as well as specific guidance on implementing the O3 NAAQS in some contexts under the CAA and the EPA regulations.
The EPA has considered the extent to which existing EPA regulations and guidance are sufficient to implement the revised standards. As a general matter, the CAA does not require that the EPA promulgate new implementing regulations or issue new guidance for states every time that a NAAQS is revised. Likewise, the CAA does not require the issuance of additional implementing regulations or guidance by the EPA before a revised NAAQS becomes effective. It is important to note that the existing EPA regulations in 40 CFR part 51 applicable to SIPs generally and to particular pollutants, including O3 and O3 precursors, continue to apply unless and until they are updated. Accordingly, the discussion below provides the EPA's current thoughts about the extent to which revisions to existing regulations and additional guidance are appropriate to aid in the implementation of the revised O3 NAAQS.
2. Additional New Rules and Guidance
The EPA has received comments from a variety of states and organizations asking for rules and guidance associated with a revised NAAQS to be issued in a timely manner. Although issuance of such rules and guidance is not a part of the NAAQS review process, National Ass'n of Manufacturers v. EPA, 750 F. 3d 921, 926-27 (D.C. Cir. 2014), toward that end the EPA intends to produce appropriate revisions to necessary implementation rules and provide additional guidance in time frames that are useful to states when developing implementation plans that meet CAA requirements.
Certain requirements under the PSD preconstruction permit review program apply immediately to a revised NAAQS upon the effective date of that NAAQS, unless the EPA has established a grandfathering provision through rulemaking. To ensure a smooth transition to a revised O3 NAAQS, the EPA is finalizing a grandfathering provision similar to the provision finalized in the 2012 PM2.5 NAAQS Rule. See section VII.C of this preamble for more details on the PSD program and the final grandfathering provision.
Promulgation or revision of the NAAQS starts a clock for the EPA to designate areas as either attainment or nonattainment. State recommendations for area designations are due to the EPA within 12 months of promulgating or revising the NAAQS. In an effort to allow states to make more informed recommendations, the EPA intends to issue guidance concerning the designations process within four months of promulgation of the NAAQS, or approximately eight months before state recommendations are due. The EPA generally completes area designations two years after promulgation of a NAAQS. See section VIII.B of this preamble for additional information on the initial area designation process.
Under CAA section 110, a NAAQS revision triggers the review and, as necessary, revision of SIPs to be submitted within three years of promulgation of a revised NAAQS. These SIPs are referred to as "infrastructure SIPs." The EPA issued general guidance on submitting infrastructure SIPs on September 13, 2013. It should be noted that this guidance did not address certain state planning and emissions control requirements related to interstate pollution transport. This guidance remains relevant for the revised O3 NAAQS. See section VIII.A.4 of this preamble for additional information on infrastructure SIPs.
The EPA intends to propose rules necessary to add clarity to air agencies' efforts to implement the revised O3 NAAQS within one year after the revised NAAQS is established. The rules would address nonattainment area classification methodologies and attainment dates, attainment plan and NNSR SIP due dates, and other required implementation programs. The EPA anticipates finalizing these rules by the time areas are designated nonattainment. Finalizing rules and guidance by this time would provide air quality management agencies with the information to develop any CAA-required SIPs associated with nonattainment areas. In an area designated as nonattainment, new major sources and major modifications at existing sources are required to comply with NNSR requirements including the application of "lowest achievable emission rate" (LAER) and emissions offsets at ratios prescribed by the CAA. See section VIII.A.5 of this preamble for additional information on nonattainment SIPs and section VIII.C.3 for additional information on NNSR.
3. Background O3
The EPA and state, local and tribal air agencies, strive to determine how to most effectively and efficiently use the CAA's various provisions to provide required public health and welfare protection from the harmful effects of O3. In most cases, reducing man-made emissions of NOX and VOCs will reduce O3 formation and provide additional health and welfare protection. The EPA recognizes, however, that "background" O3 levels, which can be significant in some areas on some days, may present a challenge to air agencies in preparing clean air plans. That is, O3 and O3-forming pollution from natural and international sources could prevent ambient levels from reaching attainment levels in locations where the impacts of such sources are large relative to the impact of controllable man-made sources of NOX and VOC emissions within the U.S.
The term "background" O3 is often used to refer to O3 that originates from natural sources of O3 (e.g., wildfires and stratospheric O3 intrusions) and O3 precursors, as well as from man-made international emissions of O3 precursors. Using the term generically, however, can lead to confusion as to what sources of O3 are being considered. Relevant to the O3 implementation provisions of the CAA, we define background O3 the same way the PA defines U.S. background (USB): O3 that would exist in the absence of any man-made emissions inside the U.S.
While the majority of modeled O3 exceedances have local and regional emissions as their primary cause, there can be events where O3 levels approach or exceed the concentration level of the revised O3 standards in large part due to background sources. These cases of high USB levels on high O3 days typically result from stratospheric intrusions of O3, wildfire O3 plumes, or long-range transport of O3 from sources outside the U.S. In most locations in the U.S., these events are relatively infrequent and the CAA contains provisions that can be used to help deal with certain events, including providing varying degrees of regulatory relief for air agencies and potential regulated entities. The EPA intends to work closely with states to identify affected locations and ensure that the appropriate regulatory mechanisms are employed.
Regulatory relief associated with U.S. background O3 may include:
   *	Relief from designation as a nonattainment area through exclusion of data affected by exceptional events;
   *	Relief from the more stringent requirements of higher nonattainment area classifications through treatment as a rural transport area, through exclusion of data affected by exceptional events, or through international transport provisions;
   *	Relief from adopting more than reasonable controls to demonstrate attainment through international transport provisions.
Further discussion of these mechanisms is provided in sections VIII.B.2 (exceptional events), VIII.B.1 (rural transport areas), and VIII.E.2 (international transport).
None of these relief mechanisms are completely burden-free, meaning they all require some level of assessment or demonstration by a state and/or the EPA to legally invoke. In no case does the CAA authorize a blanket exclusion from the basic application of an air quality management regime because an area is significantly impacted by background O3. For the revised O3 standards, the areas that would most likely need to use the relief mechanisms discussed in this section as part of attaining the revised O3 standards are locations in the western U.S. where we have estimated the largest seasonal average values of background O3 occur. As discussed in sections V.D and VIII.B.2 of this action, the EPA will soon propose revisions to the 2007 Exceptional Events Rule and will release through a Federal Register Notice of Availability a draft guidance document to address Exceptional Events Rule criteria for wildfires that could affect O3 concentrations. We expect to promulgate Exceptional Events Rule revisions and finalize the new guidance document before the October 2016 date by which states, and any tribes that wish to do so, are required to submit their initial designation recommendations for the revised O3 NAAQS.
4. Section 110 State Implementation Plans
The CAA section 110 specifies the general requirements for SIPs. Within three years after the promulgation of revised NAAQS (or such shorter period as the Administrator may prescribe) each state must adopt and submit "infrastructure" SIPs to the EPA to address the requirements of section 110(a)(1) and (2), as applicable. These "infrastructure SIPs" establish the basic state programs to implement, maintain, and enforce revised NAAQS and provide assurances of state resources and authorities. States are to develop and maintain an air quality management infrastructure that includes enforceable emission limitations, a permitting program, an ambient monitoring program, an enforcement program, air quality modeling capabilities, and adequate personnel, resources, and legal authority. Section 110(b) of the CAA provides that the EPA may extend the deadline for the "infrastructure" SIP submission for a revised secondary standard by up to 18 months beyond the initial three years. Since the revised primary NAAQS and secondary NAAQS are identical, the EPA believes it would be more efficient for states and the EPA if each affected state submits a single section 110 infrastructure SIP that addresses both standards at the same time (i.e., within three years of promulgation of the O3 NAAQS), because the EPA does not at present discern any need for there to be any significant substantive difference in the infrastructure SIPs for the two standards. Accordingly the EPA is not extending the SIP deadline for purposes of a revised secondary standard.
It is the responsibility of each state to review its air quality management program's infrastructure SIP provisions in light of each revised NAAQS. Most states have revised and updated their infrastructure SIPs in recent years to address requirements associated with 2008 NAAQS. We expect that the result of these prior updates is that, in most cases, states will already have adequate state regulations already adopted and approved into the SIP to address a particular requirement with respect to the revised O3 NAAQS. For such portions of the state's infrastructure SIP submittal, the state may provide a "certification" specifying that certain existing provisions in the SIP are adequate. Although the term "certification" does not appear in the CAA as a type of infrastructure SIP submittal, the EPA sometimes uses the term in the context of infrastructure SIPs, by policy and convention, to refer to a state's SIP submission. If a state determines that its existing EPA-approved SIP provisions are adequate in light of the revised O3 NAAQS with respect to a given infrastructure SIP element (or sub-element), then the state may make a "certification" that the existing SIP contains provisions that address those requirements of the specific CAA section 110(a)(2) infrastructure elements. In the case of a certification, the submittal does not have to include another copy of the relevant provision (e.g., rule or statute) itself. Rather, the submittal may provide citations to the already SIP-approved state statutes, regulations, or non-regulatory measures, as appropriate, which meet the relevant CAA requirement. Like any other SIP submittal, such certification can be made only after the state has provided reasonable notice and opportunity for public hearing. This "reasonable notice and opportunity for public hearing" requirement for infrastructure SIP submittals appears at section 110(a), and it comports with the more general SIP requirement at section 110(l) of the CAA. Under the EPA's regulations at 40 CFR part 51, if a public hearing is held, an infrastructure SIP submittal must include documentation by the state that the public hearing was held in accordance with the EPA's procedural requirements for public hearings. See 40 CFR part 51, Appendix V, paragraph 2.1(g), and 40 CFR 51.102.
5. Nonattainment Area Requirements
Part D of the CAA describes the various program requirements that apply to states with nonattainment areas for different NAAQS. Clean Air Act Section 182 (found in subpart 2 of part D) includes the SIP requirements that govern the O3 program, and supplements the more general nonattainment area requirements in CAA sections 172 and 173. Under CAA section 182, states generally are required to submit attainment demonstration SIPs within three or four years of the effective date of area designations by the EPA, depending on the classification of the area. These plans need to show how the nonattainment area will attain the primary O3 standard "as expeditiously as practicable," but no later than within the relevant time frame from the effective date of designations associated with the classification of the area.
Section 181(a)(1) of the CAA establishes classification categories for areas designated nonattainment for the primary O3 NAAQS. These categories range from "Marginal," the lowest O3 classification with the fewest requirements associated with it, to "Extreme," the highest classification with the most required programs. Areas with worse O3 problems are given more time to attain the NAAQS and more associated emission control requirements.
The EPA believes that the overall framework and policy approach of the implementation rules associated with the 2008 O3 NAAQS provide an effective and appropriate template for the general approach states would follow in planning for attainment of the revised O3 standard. For purposes of the revised O3 standards, the EPA intends to develop and propose a new O3 NAAQS Implementation Rule that will contain, to the extent necessary, the EPA's interpretation of the CAA's nonattainment area requirements. This will include establishing air quality thresholds associated with each nonattainment area classification (i.e., Marginal, Moderate, etc.), and deadlines for attainment planning SIPs. The rulemaking will also address whether to revoke the 2008 O3 NAAQS, and appropriate anti-backsliding requirements to ensure that the protections afforded by that standard are preserved. The EPA intends to propose this implementation rule within one year after the revised O3 NAAQS is promulgated, and finalize the implementation rule by no later than the time the area designations process is finalized (approximately two years after promulgation of the revised O3 NAAQS).
We know that developing the implementation plans that outline the steps a nonattainment area will take to meet an air quality standard requires a significant amount of work on the part of state, tribal or local air agencies. The EPA routinely looks for ways to reduce this workload, including assisting with air quality modeling by providing inputs such as emissions, meteorological and boundary conditions; and sharing national-scale model results that states can leverage in their development of attainment demonstrations.
B. O3 Air Quality Designations
1. Area Designation Process
After the EPA establishes or revises a NAAQS, the CAA directs the EPA and the states to take steps to ensure that the new or revised NAAQS is met. One of the first steps, known as the initial area designations, involves identifying areas of the country that either meet or do not meet the newer revised NAAQS, along with any nearby areas that contribute to areas that do not meet the newer revised NAAQS.
Section 107(d)(1) of the CAA provides that, "By such date as the Administrator may reasonably require, but not later than 1 year after promulgation of a new or revised national ambient air quality standard for any pollutant under section 109, the Governor of each state shall ... submit to the Administrator a list of all areas (or portions thereof) in the state" that designates those areas as nonattainment, attainment, or unclassifiable. The EPA must then promulgate the area designations according to a specified process, including procedures to be followed if the EPA intends to modify a recommendation. The CAA defines an area as nonattainment if it is violating the NAAQS or if it is contributing to a violation in a nearby area.
Clean Air Act Section 107(d)(1)(B)(i) further provides, "Upon promulgation or revision of a national ambient air quality standard, the Administrator shall promulgate the designations of all areas (or portions thereof) ... as expeditiously as practicable, but in no case later than 2 years from the date of promulgation of the new or revised national ambient air quality standard. Such period may be extended for up to one year in the event the Administrator has insufficient information to promulgate the designations." The term "promulgation," in the context of setting NAAQS, has been interpreted by the courts to be signature and widespread dissemination of a final NAAQS rule. By no later than 120 days prior to promulgating area designations, the EPA is required to notify states of any intended modifications to their recommendations that the EPA may deem necessary. States then have an opportunity to demonstrate why any proposed modification is inappropriate. Whether or not a state provides a recommendation, the EPA must timely promulgate the designation that the agency deems appropriate.
While section 107 of the CAA specifically addresses states, the EPA intends to follow the same process for tribes to the extent practicable, pursuant to CAA section 301(d) regarding tribal authority and the Tribal Authority Rule (63 FR 7254, February 12, 1998). To provide clarity and consistency in doing so, the EPA issued a 2011 guidance memorandum on working with tribes during the designation process.
As discussed in sections II and IV of this preamble, the EPA is revising both the primary and secondary O3 NAAQS. Accordingly, the EPA intends to complete designations for both NAAQS following the standard 2-year process discussed above. In accordance with section 107(d)(1) of the CAA, state Governors (and tribes, if they choose) should submit their initial designation recommendations for a revised primary and secondary NAAQS no later than 1 year after promulgation of the revised O3 NAAQS, that is by [INSERT DATE OF SIGNATURE]. If the EPA intends to modify any state recommendation, the EPA would notify the appropriate state Governor (or tribal leader) no later than 120 days prior to making final designation decisions. A state or tribe that believes the modification is inappropriate would then have the opportunity to demonstrate to the EPA why it believes its original recommendation (or a revised recommendation) is more appropriate. The EPA would take any additional input into account in making the final designation decisions.
Consistent with previous area designations processes, the EPA intends to use area-specific analysis of multiple factors to support area boundary decisions. The EPA intends to evaluate information related to the following factors for designations: air quality data, emissions and emissions-related data, meteorology, geography/topography, and jurisdictional boundaries. Additional guidance on the designation process and how these factors are informed and evaluated will be issued by the EPA early in 2016 to assist states in developing their recommendations.
Areas that are designated as nonattainment are also classified at the time of designation by operation of law according to the severity of their O3 problem. The classification categories are Marginal, Moderate, Serious, Severe, and Extreme. Ozone nonattainment areas are subject to specific mandatory measures depending on their classification. As indicated previously, the thresholds for the classification categories will be established in a future O3 implementation rule.
Clean Air Act section 182(h) authorizes the EPA Administrator to determine that an area designated nonattainment can be treated as a rural transport area. Regardless of its classification, a rural transport area is deemed to have fulfilled all O3-related planning and control requirements if it meets the CAA's requirements for areas classified Marginal, which is the lowest classification specified in the CAA. In accordance with the statute, a nonattainment area may qualify for this determination if it meets the following criteria:
   *	The area does not contain emissions sources that make a significant contribution to monitored O3 concentrations in the area, or in other areas; and
   *	The area does not include and is not adjacent to a Metropolitan Statistical Area.
Historically, the EPA has recognized a few nonattainment areas under this statutory provision. The EPA has not issued separate written guidance to further elaborate on the interpretation of these CAA qualification criteria. However, the EPA developed draft guidance in 2005 that explains the kinds of technical analyses that states could use to establish that transport of O3 and/or O3 precursors into the area is so overwhelming that the contribution of local emissions to an observed 8-hour O3 concentration above the level of the NAAQS is relatively minor and determine that emissions within the area do not make a significant contribution to the O3 concentrations measured in the area or in other areas. While this guidance was not prepared specifically for rural transport areas, it could be useful to states for developing technical information to support a request that the EPA treat a specific O3 nonattainment area as a rural transport area. The EPA will work with states to ensure all nonattainment areas eligible for treatment as rural transport areas are identified.
2. Exceptional Events
During the initial area designations process, the EPA intends to evaluate multiple factors, including air quality data, when identifying and determining boundaries for areas of the country that meet or do not meet the revised O3 NAAQS. In some cases, these data may be influenced by exceptional events. Under the Exceptional Events Rule, an air agency can request and the EPA can agree to exclude data associated with event-influenced exceedances or violations of a NAAQS, including the revised O3 NAAQS, provided the event meets the statutory requirements in section 319(b) of the CAA:
   *	The event "affects air quality."
   *	The event "is not reasonably controllable or preventable."
   *	The event is "caused by human activity that is unlikely to recur at a particular location or [is] a natural event."
The EPA's implementing regulations, the Exceptional Events Rule, further specify that air agencies must provide evidence that:
   *	"There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality in the area;"
   *	"The event is associated with a measured concentration in excess of normal historical fluctuations, including background;" and
   *	"There would have been no exceedance or violation but for the event."
The ISA contains discussions of natural events that may contribute to O3 or O3 precursors. These include stratospheric O3 intrusion and wildfire events. As indicated above, to satisfy the exceptional events requirements and to qualify for data exclusion under the Exceptional Events Rule, an air agency must develop and submit evidence addressing each of the identified criteria. The extent to which a stratospheric O3 intrusion event or a wildfire event contribute to O3 levels can be uncertain, and in most cases requires detailed analyses to determine.
Strong stratospheric O3 intrusion events, most prevalent at high elevation sites during winter or spring, can be identified based on measurements of low relative humidity, evidence of deep atmospheric mixing, and a low ratio of CO to O3 based on ambient measurements. Accurately determining the extent of weaker intrusion events remains challenging (U.S. EPA 2013, p. 3-34). Although states have submitted only a few exceptional event demonstrations for stratospheric O3 intrusion, the EPA recently approved a demonstration from Wyoming for a June 2012 stratospheric O3 event.
While stratospheric O3 intrusions can increase monitored ground-level ambient O3 concentrations, wildfire plumes can either suppress or enhance O3 depending upon a variety of factors including fuel type, combustion stage, plume chemistry, aerosol effects, meteorological conditions and distance from the fire (Jaffe and Wigder, 2012). As a result, determining the impact of wildfire emissions on specific O3 observations is challenging. The EPA recently approved an exceptional event demonstration for wildfires affecting 1-hour O3 levels in Sacramento, California in 2008 that successfully used a variety of analytical tools (e.g., regression modeling, back trajectories, satellite imagery, etc.) to support the exclusion of O3 data affected by large fires.
In response to previously expressed stakeholder feedback regarding implementation of the Exceptional Events Rule and specific stakeholder concerns regarding the burden of exceptional event demonstrations, the EPA is currently engaged in a rulemaking process to amend the Exceptional Events Rule. As part of an upcoming notice and comment rulemaking effort (and related activities, including the issuance of guidance documents), the EPA sees opportunities to standardize best practices for collaboration between the EPA and air agencies, clarify and simplify demonstrations, and improve tools and consistency.
Additionally, the EPA intends to develop guidance to address implementing the Exceptional Events Rule criteria for wildfires that could affect ambient O3 concentrations. Wildfire emissions are a component of background O3 (Jaffe and Wigder, 2012) and in some locations can significantly contribute to periodic high O3 levels (Emery, 2012). The threat from wildfires can be mitigated through management of wildland vegetation. Planned and managed fires are one tool that land managers can use to reduce fuel load, unnatural understory and tree density, thus helping to reduce the risk of catastrophic wildfires. Allowing some wildfires to continue and the thoughtful use of prescribed fire can influence the occurrence of catastrophic wildfires, which may reduce the probability of fire-induced smoke impacts and subsequent health effects. Thus, appropriate use of prescribed fire may help manage the contribution of wildfires to both background and periodic peak O3 air pollution.
The EPA is committed to working with federal land managers, other federal agencies, tribes and states to effectively manage prescribed fire use to reduce the impact of wildfire-related emissions on O3 through policies and regulations implementing these standards.
C. How do the New Source Review (NSR) Requirements apply to the Revised O3 NAAQS?
1. NSR Requirements for Major Stationary Sources for the Revised O3 NAAQS
      The CAA, at parts C and D of title I, contains NSR requirements that constitute preconstruction review and permitting programs applicable to new major stationary sources and major modifications of existing major sources. The preconstruction review of each new major stationary source and major modification generally applies on a pollutant-specific basis, and the requirements that apply for each pollutant generally depend on whether the area in which the source is situated is designated as attainment (or unclassifiable) or nonattainment for that pollutant. In areas designated attainment or unclassifiable for a pollutant, the PSD requirements under part C apply. In areas designated nonattainment for a pollutant, the nonattainment area NSR (NNSR) requirements under part D apply. Collectively, those two sets of permit requirements are commonly referred to as the "major NSR programs."