We disagree with the comments calling for more stringent 2008 standards than proposed for 25   75 hp engines, based on the use of diesel oxidation catalysts. The standards we proposed and are adopting for these engines pull ahead sizeable PM reductions starting three years ahead of the earliest PM filter based standards for any engine size. The pull ahead standard level balances early reductions with the need to ensure that the PM filter based standards and Tier 3 NMHC+ NO X standards are not jeopardized by an overemphasis on early reductions. Although we agree that oxidation catalysts can be applied to these engines, the emissions performance data we have analyzed do not support our setting a more stringent standard, for the same reasons described above in section II. A. 3. a for engines under 25 hp. Refer to section II. B. 4 and to section 4.1.4 of the RIA for additional discussion. For a discussion of comments opposed to new standards in 2008, see sections II. A. 1 and II. B of this preamble.

We also do not agree that more stringent NO X requirements based on improved engine optimization are appropriate for these engines in 2008. In 2001 we reviewed and confirmed the previously set NMHC+ NO X emission standards that will be in effect for these engines during the time frame in question. 31 Because of the focus we are putting on achieving large PM reductions from these engines as early as possible, we felt that it was important to strike a balance between PM and NO X control. As a result, we did not propose more stringent NO X standards for 50   75 hp engines, and we proposed to apply the 3.5 g/ bhp hr NMHC+ NO X standard to 25 50 hp engines in 2013 because this is the year in which the PM filter based standard is being implemented. Requiring new NO X controls for these engines earlier than 2013 would add a third redesign step to those already called for in 2008 and 2013. This would add a potentially 45 unacceptable amount of redesign workload, to a point that it could jeopardize our objective of bringing stringent PM control to these engines as early as possible.

Consistent with the proposal, we are not setting more stringent NO X standards for engines below 75 hp at this time based on the use of NO X aftertreatment. As discussed in section <IP_ADDRESS> of the RIA, a high degree of complexity and engine/ aftertreatment integration will be involved in applying NO X adsorber technology to nonroad diesel engines. The similarity of larger nonroad engines ( above 75 hp) to highway diesel engines, which will provide the initial experience base for this integration process, is key to our assessment that NO X adsorbers are feasible for these engines. On the other hand, although engines under 75 hp are gradually increasing in sophistication over time, the accumulation of experience with designing and operating these engines with more advanced technology clearly lags significantly behind the sizeable experience base already developed for larger engines. At this point, we are unable to forecast how quickly adequate experience may accrue. Because this experience is crucial to ensuring the successful integration of the engines with NO X adsorber technology, we are not adopting NO X adsorberbased standards for engines under 75 hp in this final rule. Rather, as discussed in section VIII. A, we plan to undertake a technology assessment in the 2007 time frame which would evaluate the status of engine and emission control technologies, including NO X controls, for engines less than 75 hp.

As described in section II. A. 1. a, we are providing two PM standard compliance options to engine manufacturers for 50 75 hp engines. As part of this, we also proposed a measure to ensure that it would not be abused by equipment manufacturers who use engines that do not meet the PM pull ahead standard in 2008 2011, but who then switch engine suppliers to avoid PM filter equipped engines in 2012 as well ( 68 FR 28360, May 23, 2003). We proposed that an equipment manufacturer making a product with engines not meeting the pull ahead standard in any of the years 2008   2011 must use engines in that product in 2012 meeting the 0.02 g/ bhp hr PM standard; that is, the equipment manufacturer would have to use an engine from the same engine manufacturer or from another engine manufacturer choosing the same compliance option. We also solicited comment on possible alternative solutions using a numerical basis, describing an example that would require the percentage of 50   75 hp machines equipped with PM filters in 2012 to be no less than the same percentage of 50   75 hp machines produced with non pull ahead engines in 2008   2011.

The Engine Manufacturers Association ( EMA) and Deere commented on the unenforceability of the proposed " no switch" measure as part of a broader objection to our proposal for 50   75 hp engines. They pointed out that changing equipment model designations could easily allow an equipment manufacturer seeking to avoid PM filter equipped engines in 2012 to declare a product in this model year a " new product," not the same as the 2008   2011 product. We have concluded that there is indeed potential for this abuse to occur and, although no one commented specifically on the alternative approach, we believe it clearly addresses this problem because it does not depend on product designations. 32 The 2011 production is not included in the percentage calculation to avoid the need for post

2011 confirmation of production volumes which, as it would occur in 2012, would be too late to easily refocus 2012 production if the confirmed volumes differ from projections. It is not likely that manufacturers would abuse the program by switching engine suppliers for this one year of production.

33 That is: [ 200/( 1000 500)] = 40%; subtracting the 5% margin then yields 35%.

46 Therefore, we are adopting a provision to discourage engine switching based on this alternative approach. An equipment manufacturer who uses 50   75 hp engines will have three options:

1) The manufacturer may exclusively use engines certified to the 0.22 g/ bhp hr PM standard ( including through use of ABT credits) over the 2008 2011 period. This manufacturer is then free to use any number of 50   75 hp engines not certified to the 0.02 g/ bhp hr standards in 2012. 2) The manufacturer may exclusively use engines not certified to the 0.22 g/ bhp hr PM standard over the 2008   2011 period. This manufacturer must then use only 50   75 hp engines that are certified to the 0.02 g/ bhp hr standards in 2012 ( including through use of ABT credits). 3) The manufacturer may use a mix of engines in 2008   2011. In this case, the manufacturer must calculate the percentage of 50   75 hp engines used ( in U. S. directed equipment) over the 2008   2010 period that are not certified to the 0.22 g/ bhp hr PM pull ahead standard. Then the percentage of 50   75 hp engines this manufacturer uses in 2012 that are certified to the 0.02 g/ bhp hr PM standard must be no less than this 2008   2010 non pull ahead percentage figure minus a 5% margin. 32 As an example of this third option, consider an equipment manufacturer who does not use the transition flexibility provisions ( described in section III. B), and over the 2008   2010 period makes 1000 50   75 hp machines for use in the U. S., 200 ( 20%) of which use engines not certified to the 0.22 g/ bhp hr standard. In 2012, that manufacturer must make at least 15% of his 50   75 hp machines for use in the U. S. using engines certified to the 0.02 g/ bhp hr standard. We feel that the 5% margin is needed to allow for some reasonable sales shifts within the manufacturer's product offering over time, but is small enough to ensure that any possible advantage gained from selling higher emissions products remains minimal. Equipment manufacturers must keep production records sufficient to prove compliance. This restriction and the percentage calculation will not apply to any 2008   2012 engines at issue that are being produced under the equipment manufacturer transition flexibility provisions discussed in section III. B. For example, if in addition to the 200 engines in 2008 2010 not certified to the 0.22 g/ bhp hr standard in the above example, this manufacturer also used 500 previous tier engines in 2008   2010 under the flexibility allowance program, his percentage target for PM filter equipped engines in 2012 would be 35% of all the engines used in 2012 that are not previous tier engines under the flexibility allowance program. 33 47 4. Standards for Engines Above 750 hp We are adopting different Tier 4 standards for over 750 hp engines from those we proposed, and we are also adopting different implementation dates for these engine standards, though both the proposed and final programs have as their primary focus the implementation of high efficiency exhaust emission controls as quickly as possible. The approach being adopted reflects our careful review of the technical issues presented by these engines. For some of these engines, we are accelerating standards based on the use of aftertreatment controls. For others, we are deferring a decision on such aftertreatment based standards. This approach represents a feasible and efficient approach to redesigning engines and installing aftertreatment in a coordinated, orderly manner over a decade or more, and will achieve major reductions in PM and NO X from these large diesel engines.

Under the proposal, all engines above 750 hp were treated the same, with a phase in of PM and NO X aftertreatment technology that started in 2011 and finished in 2014. The final standards are based on our evaluation of the differing technical issues presented by the two primary kinds of equipment in this category, mobile power generation equipment ( generator sets) and mobile machinery. For both generator sets and mobile machinery, PM aftertreatment based standards will start in 2015, with no prior phase in. EPA is replacing the proposed phase in with a PM standard starting in 2011 that is comparable to the overall level of control that the proposed phase in would achieve. Differences within these applications, however, call for different approaches to the implementation of NO X aftertreatment technology. For generator sets above 1200 hp, an aftertreatment based NO X standard will start in 2011, three years earlier than the date we proposed for full implementation of such standards. For generator sets below 1200 hp, the same aftertreatment based NO X standard will start in 2015. As with the PM standard, there is no phase in. For engines used in mobile machinery, which is assumed to include all equipment that is not a generator set, EPA is deferring a decision on setting aftertreatment based NO X standards to allow additional time to evaluate the technical issues involved in adapting NO X adsorber technology to these applications and engines. However, EPA is adopting a NO X standard for these engines starting in 2011 that will achieve large NO X reductions by relying on engine based emissions control technology. Consistent with the different approaches we are taking to setting standards for engines above and below 750 hp, we are also adopting restrictions on ABT credit use between these power categories, as described in section III. A.

Consistent with the approach we took in previous standard setting for these engines, we proposed that nonroad diesels above 750 hp be given more lead time than engines in other power categories to fully implement Tier 4 standards, due primarily to the relatively long product design cycles typical of these high cost, low sales volume engines and machines. Specifically, we proposed that this category of engines move directly from Tier 2 to Tier 4, and that the Tier 4 PM standard be phased in for these engines on the same 50 50 50 100% schedule as the NO X and NMHC phase in schedule, over the 2011   2014 model years. This would provide engine manufacturers with up to 8 years of design stability to address concerns specific to this category. Although we expressed our belief that these proposed provisions would enable the manufacturers 48 to meet proposed Tier 4 engine standards, we also acknowledged concerns the manufacturers had expressed to us, and asked for comment on whether this category, or some subset of it defined by hp or application, should have a later phase in start date, a later phase in end date, adjusted standards, additional equipment manufacturer transition flexibility provisions, or some combination of these ( 68 FR 28364, May 23, 2003).

Comments from manufacturers of engines and equipment in this power category expressed their widespread view that the proposed standards were inappropriate in critical respects. In addition to reiterating the need for extra lead time due to long product design cycles, they pointed to difficulties with aftertreatment placement, with fabrication of the large filters that would be needed for these engines, with potential failures caused by uneven soot loading and regeneration in large filters, with stresses due to thermal gradients across large filters, and with mechanical stresses in mining applications with high shock loads. The manufacturers noted that aftertreatment based standards for NO X and PM were feasible for engines used in large mobile power generators. However, manufacturers did not believe aftertreatment based NO X standards could be implemented in the time frame proposed for engines used in large mobile machinery such as bulldozers and mine haul trucks. States, environmental organizations, and manufacturers of emissions controls, on the other hand, expressed support for the standards we proposed for these engines.

After evaluating these issues, EPA is adopting an approach that tailors the standards to the circumstances presented by the different kinds of engines in this power category. The NO X standards we are adopting will achieve effective NO X control by accelerating the proposed schedule for final NO X standards based on high efficiency NO X aftertreatment for the largest generator sets, and by requiring engines in other generator sets to also meet aftertreatment based NO X standards, although we are delaying the implementation date for these standards compared to the implementation schedule we proposed. We believe that NO X adsorber technology will be feasible for these generator set engines. We also believe that they may be an especially attractive application for Selective Catalytic Reduction ( SCR) technology, which relies on the injection of urea into the exhaust stream. There are many stationary diesel generator sets using SCR today. Large mobile generator sets, though moved from location to location, operate much like stationary units once in place, with fuel ( and potentially urea) delivered and replenished periodically. See section II. B. 3 for further discussion.

For equipment other than generator sets, we are deferring a decision on setting aftertreatment based NO X standards to allow additional time to evaluate the technical issues involved in adapting NO X control technology to these applications and engines. We are still evaluating the issues involved for these engines to achieve a more stringent NO X standard, and believe that these issues are resolvable. We intend to continue evaluating the appropriate longterm NO X standard for mobile machinery over 750 hp and expect to announce further plans regarding these issues ( we are currently considering such an action in the 2007 time frame). The basis for the 0.50 g/ bhp hr NO X standard we are adopting for generator sets over 750 hp is discussed in section II. B. 3. We are also modifying the PM and NMHC standards we proposed ( as 49 well as certain implementation dates for these provisions), and modifying our proposed approach to ensuring transient emissions control for these engines ( discussed in section III. F). The Tier 4 standards for engines over 750 hp are shown in table II. A 4.

Table II. A 4.   Tier 4 Standards for Engines Over 750 hp ( g/ bhp hr)

engines used in: 2011 2015 PM NO X NMHC PM NO X NMHC generator sets

1200 hp 0.075 2.6 0.30 0.02 0.50 0.14 generator sets > 1200 hp 0.075 0.50 0.30 0.02 no new standard 0.14 all other equipment 0.075 2.6 0.30 0.03 no new standard 0.14 Unlike NO X control technology, we believe that the more advanced state of PM filter technology development today makes their availability for these engines by 2015, with over ten years of development lead time, more certain, and so we are setting PM standards for both mobile machinery and generator sets based on use of this technology. We note in section II. B. 3 that achieving durable PM filter designs for these large applications will likely require the use of wire mesh filter technology rather than the somewhat more efficient wall flow ceramic based technology applicable to smaller engines, justifying the somewhat higher level for the 2015 PM standards shown in table II. A 4 ( 0.03 or 0.02 g/ bhp hr compared to 0.01 g/ bhp hr). Section II. B. 3 also contains discussion of our bases for the other Tier 4 standard levels in this category. We believe that the 2015 implementation year ( versus the proposed 2014 date for the fully phased in standard) is necessary to allow development of the requisite technologies for these large engines, and to deal with the redesign workload Tier 4 will create for the many engine and equipment models in this category which, as noted, typically have very low production volumes and long product cycles.

For the purpose of determining which nonroad engines are subject to the generator set standards, we are defining a generator set engine as: " An engine used primarily to operate an electrical generator or alternator to produce electric power for other applications." This definition makes it clear that generator set engines do not include engines used in machines such as mine trucks that do mechanical work but that employ engine powered electric motors to propel the machine, but they do include engines in nonroad equipment for which the primary purpose is to generate electric power, even if the machine is also self propelled.

Similar to other power categories, we proposed a 50% phase in to the final Tier 4 PM, NO X and NMHC standards, with opportunity to average PM and NO X between phase in and phase out engines in the 2011 2013 phase in years via the ABT program. Because in this rule we are no longer phasing in to a final NO X standard for some engines over 750 hp, it no longer makes 50 sense to express the 2011 standards for these engines in this manner. Instead we are setting brake specific emission standards effective in 2011. Furthermore, to avoid further complicating an already complex standards structure, we are adopting this pattern for the entire category, even with engines such as those used in generator sets for which the standards could still be expressed as a percent phase in to final standards. Except for the pull ahead of the long term NO X standard for large generator sets ( which will increase the environmental benefit compared to the proposal), these 2011 PM and NO X standards essentially correspond to averaged standards under a 50% phase in to aftertreatment based standards, hence our conclusion that the Tier 4 program will provide a level of control in 2011 that is substantially equivalent to that of the proposal. In addition, PM and NO X emissions averaging through the ABT program will allow a manufacturer to comply by phasing in aftertreatment technologies as in the proposed program, should they desire to do so. Although there is no such averaging program for NMHC, the 2011 NMHC standard can be achieved without the use of advanced aftertreatment ( as explained in section II. B. 3), thus helping to enable a manufacturer to pursue this compliance strategy if desired.

This approach involving separate 2011 and 2015 standards is comparable to the proposed percent phase in approach with emissions averaging. We believe that it enables manufacturers to redesign engines and equipment in a coordinated, orderly manner over a decade or more, and effectively gives targeted additional flexibility to the industry. Given the continuing availability of emissions averaging, we do not view this change as the creation of an additional, separate tier of standards compared to the proposal's phase in of the Tier 4 standards.

5. Establishment of New Power Categories We are finalizing our proposal to regroup the nine power categories established for previous tiers into the five Tier 4 power categories shown in table II. A 1. As we explained in the proposal, this regrouping will more closely match the degree of challenge involved in transferring advanced emissions control technology from highway engines to nonroad engines. The proposed choice of 75 hp as the appropriate cutpoint for applying aftertreatment based NO X control drew particular attention. In the proposal, we recognized that there is not an abrupt power cutpoint above and below which the highway derived nonroad engine families do and do not exist, but noted further that 75 hp is a more appropriate cutpoint to generally identify nonroad engines in Tier 4 that will most likely be using highway like engine technology than either of the closest previously adopted power category cutpoints of 50 or 100 hp. Nonroad diesels produced today with rated power above 75 hp ( up to several hundred hp) are mostly variants of nonroad engine platforms with four or more cylinders and per cylinder displacements of one liter or more. These in turn are largely derived from or are similar to heavy duty highway engine platforms. Even where nonroad engine models above 75 hp are not so directly derived from highway models, they typically share many common characteristics such as displacements of one liter per cylinder or more, direct injection fueling, turbocharging, and, increasingly, electronic fuel injection. These common features provide key building blocks in transferring high efficiency exhaust emission control technology from highway to similar nonroad diesel engines. We therefore proposed to regroup power ratings using the 75 hp cutpoint. 51 The Engine Manufacturers Association and Euromot, which together represent the companies that make all but a tiny fraction of nonroad diesel engines sold in the U. S., expressed their support for the 75 hp cutpoint, as did every individual engine manufacturer who commented on this subject. These companies generally endorsed EPA's reasoning that the 75 hp level is appropriate to " delineate those engines ( and applications) for which the application of on highway like NO X aftertreatment technologies is not likely to be feasible or practical" ( EMA Comments p. 10).

However, the Association of Equipment Manufacturers ( AEM) and the equipment manufacturer Ingersoll Rand commented that 100 hp is the more appropriate cutpoint for application of advanced NO X control technology. They based this view on their observations that 75 100 hp engines do not share many of the characteristics of highway diesels, thus making technology transfer from the highway sector very costly, and customers will be negatively affected due to the relatively large cost impacts of NO X aftertreatment on these smaller engines. They also argued that the 75 hp cutpoint would create significant misalignment in the global marketplace because European regulations do not use this cutpoint.

We agree with the equipment manufacturers' observation that there are engines above 75 hp without turbocharging or electronic controls. However, EPA did not choose the 75 hp cutpoint with the expectation that all engines above it had the same technology characteristics. There is a continuum in the degree to which key technology characteristics exist on engines throughout the power spectrum, and the 75 hp cutpoint was based on information from the current fleet of engines and on manufacturers' and EPA's expectations for future design trends, showing there is a marked difference in the prevalence of these and other key engine design characteristics for engines above and below 75 hp, and that, over time, 75   100 hp engines increasingly share advanced technology characteristics common in larger engines. Clear evidence of this trend over recent model years is documented in the RIA, section 4.1.4. As discussed in section II. B. 2, the kind of engine technology generally employed by engines in the 75   100 hp range, combined with the lead time and phase in provided for the Tier 4 NO X standards, leads us to conclude that highway like NO X aftertreatment can be transferred to these engines. In addition, since our proposal, the Council of the European Union ( EU) has issued a revised final version of new nonroad diesel emission standards that essentially aligns their power cutpoints with our own, including adoption of the 75 hp cutpoint for advanced technology NO X control. EPA does not believe that the costs of meeting the NO X standard for engines in the 75 100 hp range are unreasonable, and we refer the reader to section VI for a detailed discussion of our cost analysis for engines and equipment meeting Tier 4 standards in this power range. Moreover, EPA firmly believes such standards are technologically feasible for 75   100 hp engines. ( See section II. B. 2.)

Ingersoll Rand also expressed concern that the proposed consolidation of 3 previous power categories into a single 175   750 hp category creates significant hardship by requiring the introduction of aftertreatment technologies in a single year, contrasting this with the Tier 2 standards, which phased in over 2001   2003 for these engines. In response, we note that the Tier 52 3 standards, which were set in the same rule that established the Tier 2 standards, will be introduced in a single year for these engines ( 2006), and that the Tier 2 phase in over 3 years was established in response to particular issues and opportunities that were identified, specific to that time frame ( see 62 FR 50181, September 24, 1997). In addition to the gradual phase in of Tier 4 standards over several years, we are adopting significant flexibility provisions specifically to provide adequate lead time for equipment manufacturers to make the transition to the new standards, including some provisions that provide additional flexibility from what we proposed, as explained in section III. B.

6. CO Standards We proposed minor changes in CO standards for some engines solely for the purpose of helping to consolidate power categories. We stated in the proposal that we were not exercising our authority to revise the CO standard for the purpose of improving air quality, but rather for purposes of administrative efficiency. However, manufacturers objected to these proposed changes, citing technological feasibility concerns, and a lack of parity with highway diesel and nonroad spark ignition engines, given that existing CO standards levels for nonroad engines are already five times lower than the standard level for highway engines.

Because we proposed the CO standard changes for the sake of simplifying and consolidating power categories and not because of any technical considerations relating to emission reductions, we do not believe it productive to take issue with the views expressed that these proposed changes raise serious feasibility concerns. We instead are withdrawing this aspect of the proposal, the result being that the existing CO standards remain in place. In doing so, we are not considering or reexamining ( and at proposal did not consider or reexamine) the substantive basis for those standards. Having multiple CO standards within a power category will, at worst, create minor inconveniences in certification and compliance efforts. As a result, in the less than 25 hp category, Tier 4 engines below 11 hp will continue to be subject to a different CO standard than 11   25 hp engines, identical to Tier 2. Likewise, different CO standards will continue to apply in Tier 4 to engines above and below 50 hp in the 25   75 hp category.

We do note, however, that we are applying new certification tests to all pollutants covered by the rule, the result being that Tier 4 engines will have to certify to CO standards measured by the transient test ( NRTC) ( which includes a cold start test), and the NTE. Our intent in adopting these new certification requirements is not to alter the level of stringency of the standard but rather to ensure robust control of emissions to this standard in use. The CO standards remain readily achievable using these tests, and we anticipate that no additional engine adjustments are necessary for the standards to be achievable ( so there are no significant associated costs). We also explain there that the CO standards can be achieved without jeopardizing the ability to achieve all of the other engine standards. 53 7. Crankcase Emissions Control We currently require the control of crankcase emissions from naturally aspiriated nonroad diesel engines. We proposed to extend this requirement to turbocharged nonroad diesel engines as well, starting in the same model year that Tier 4 exhaust emission standards first apply in each power category.

EMA opposed the proposed extension, reiterating concerns expressed in comments on a similar proposed provision in the 2007 heavy duty highway rule, including concerns over the impact that recirculating crankcase emissions may have on the feasibility of engine standards over the full useful life. These concerns are addressed in the Summary and Analysis of Comments document for that rule, which is included in the docket for today's rule. Besides the feasibility issues raised by EMA for nonroad diesels that are addressed in the highway rule, two nonroadspecific issues were raised as well: ( 1) the need to design crankcase emission control systems that operate at the high angularity experienced by some nonroad machines on uneven ground, and ( 2) the concern that this requirement adds to the large number of " first time" requirements being adopted for Tier 4. We agree that high angularity operation may add new design considerations for these controls, but do not see how it would pose a serious barrier that could not be overcome in time. The grouping of new EPA requirements in a specific model year is an important objective of our program aimed at providing stability to the design process, a goal much supported by the engine manufacturers. We have accounted for this in assessing feasibility, costs, and flexibility needs for the program. One flexibility we are providing is the three path opportunity to satisfy our crankcase control requirement, as described below. In fact, in its written comments EMA recommended that, if EPA were to proceed with crankcase emission control requirements for Tier 4, it adopt all three options for demonstrating compliance. This is indeed what we are doing.

Thus, as proposed, in addition to allowing for compliance through the routing of crankcase emissions to the engine air intake system, we are also allowing manufacturers to instead meet the requirement by routing the crankcase gases into the exhaust stream, provided they keep the combined total of the crankcase emissions and the exhaust emissions below the applicable exhaust emission standards. Also as proposed, we are allowing manufacturers to instead meet the requirement by measuring crankcase emissions instead of completely eliminating them, provided manufacturers add these measured emissions to exhaust emissions in assessing compliance with exhaust emissions standards. Manufacturers using this option must also modify their exhaust deterioration factors or develop separate deterioration factors to account for increases in crankcase emissions as the engine ages, and must ensure that crankcase emissions can be readily measured in use. We see no reason to treat naturally aspirated engines differently than turbocharged engines, and so are allowing these options for all Tier 4 engines subject to the crankcase control requirement, both turbocharged and naturally aspirated. The wording of the proposed regulations limiting the options to turbocharged engines was inadvertent. 34 Council of the European Union, " Directive of the European Parliament and of the Council amending Directive 97/ 68/ EC", March 15, 2004.

54 8. Prospects for International Harmonization We received numerous comments, especially from engine and equipment manufacturers, stressing the need for EPA to work with other governmental standards setting bodies to harmonize standards. We recognize the importance of harmonization of international standards and have worked diligently with our colleagues in Europe and Japan to achieve that objective. Harmonization of these standards will allow manufacturers continued access to world markets and lower the required research and development and tooling costs needed to meet different standards. We will continue to work with standards setting governmental entities and with foreign and domestic manufacturers.

In October 2003, the Council and Parliament of the European Union reached agreement on revisions to a proposal developed by the European Commission that would amend Directive 97/ 68/ EC to include nonroad diesel emissions standards similar to those in our Tier 4 program, and, as in the U. S., coordinated with low sulfur diesel fuel requirements in the Europe. This revised proposal has since been finalized. 34 This revised Directive aligns well with our program in the Tier 4 time frame, even more so than did the original Commission proposal. It also closely aligns with our Tier 3 standards in the Tier 3 time frame.

For engines of 50   750 hp, the Directive's standards are very closely aligned with our own Tier 4 standards, including emissions levels, implementation dates, the defined power categories, and the lower hp limit of NO X control based on high efficiency exhaust emission controls ( 75 hp). Exceptions are noted below: ° The 2008 PM standard level for 50   75 hp engines ( the equivalent of 0.3 g/ bhp hr vs our 0.22 g/ bhp hr level). Note, however, that we do allow certification to the 0.3 g/ bhp hr level as an option, provided the manufacturer must then meet our 0.02 g/ bhp hr standard in 2012, one year earlier than otherwise. ° The 2013 PM standard level for 50   75 hp engines ( the equivalent of 0.01 g/ bhp hr vs our 0.02 g/ bhp hr level). ° An October 1, 2014 start for the final 75   175 hp NO X standard ( the same as our proposed date), compared to the December 31, 2014 date we are adopting in this final rule. ° For constant speed engines: no Tier 4 equivalent standards. Also, the EU's Tier 3 equivalent standards are not implemented on these engines until 2011   2012.

As the EU program does not provide for emissions averaging, the alternative NO X standards we are setting for 75   750 hp engines are the NO X levels at which the EU standards are generally aligned during our NO X phase in years. The EU Directive also includes transition flexibility provisions for equipment manufacturers similar to those in our program, discussed in section III. B. 55 The EU program for nonroad diesels has not adopted or proposed any current or future standards for engines above 750 hp or below 25 hp, and its revised Directive for 25   50 hp engines does not subject them to any future standards beyond those entering into force in 2007 ( equivalent to 0.45 g/ bhp hr PM and 5.6 g/ bhp hr hydrocarbon+ NO X), in contrast to our 2013 standards based the use of PM filters and more advanced engine based control technologies ( 0.02 g/ bhp hr PM and 3.5 g/ bhp hr NMHC+ NO X). However, as discussed further in section VIII. A, the EU Directive includes plans to conduct a future technology review of appropriate standards for engines below 50 hp and above 750 hp. The year that this is planned for is 2007, the same year in which we are planning a technology review for engines below 75 hp. Considering progress to date, and announced plans for reviews in 2007, we believe that prospects for harmonized standards are excellent.

9. Exclusion of Marine Engines For reasons outlined in the proposal, we are not applying Tier 4 standards to the marine diesel engines under 50 hp that are covered under our Tier 1 and 2 standards. We believe it is more appropriate to consider more stringent standards for a range of marine diesel engines, including these, in a future action. It should be noted that the existing Tier 2 standards will continue to apply to marine diesel engines under 50 hp until that future action is completed. We did not receive any adverse comments on this proposed approach.

B. Are the New Standards Feasible?

Today we are finalizing a program of stringent new standards for a broad category of nonroad diesel engines coupled with a new nonroad diesel fuel standard that dramatically lowers the sulfur level in nonroad diesel fuel ultimately to 15 ppm. We believe these standards are technically feasible in the leadtime provided given the availability of 15 ppm sulfur fuel and the rapid progress to develop the needed emission control technologies. We acknowledge, as pointed out by a number of commenters, that these standards will be challenging for industry to meet, in part due to differences in operating conditions and duty cycles for nonroad equipment and the diesel engines used in that equipment. Also, we recognize that transferring and effectively applying these technologies, which have largely been developed for highway engines, will require additional time after the application of the technology to on highway engines. Diesel engine industry commenters and environmental stakeholder commenters on our proposal consistently agreed with our position that for most engine horsepower categories the technologies to meet the standards exist and that the transfer of these technologies to nonroad is possible. The biggest difference of opinions in the range of comments received by the Agency concerns the timing of the emission standards and the flexibility provisions ( i. e., the leadtime necessary to transfer the technology). One of the most important tasks for a feasibility analysis is to determine the appropriate amount of development time needed to successfully bring new technologies to market. We have carefully weighed the desire to have clean engines sooner, with the challenges yet to be overcome in applying the technologies to nonroad engines and equipment, in determining the appropriate timing and emission levels for the standards finalized today. 35 Regulatory Impact Analysis: Heavy Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements, United States Environmental Protection Agency, December 2000,

EPA420 R 00 026. Copy Available in EPA Air Docket A 2001 28 Item II A 01.

36 Regulatory Impact Analysis: Control of Emissions of Air Pollution from Highway Heavy Duty Engines, United States Environmental Protection Agency, June 2000, EPA420 R 00 010. Copy available in EPA Air Docket A 2001 28 Item II A 02.

37 Highway Diesel Progress Review, United States Environmental Protection Agency, June 2002, EPA 420 R 02 016. Copy available in EPA Air Docket A 2001 28 Item II A 52.

38 Highway Diesel Progress Review Report 2, United States Environmental Protection Agency,

March 2004, EPA420 R 04 004. Copy available in Docket OAR 2003 0012 0918.

56 The RIA associated with today's action contains a detailed description and analysis of diesel emission control technologies, issues specific to applying these technologies to nonroad engines, and why we believe the new emission standards are feasible. Additional in depth discussion of these technologies can be found in the final RIA for the HD2007 emission standards, the final RIA for the HD2004 emission standards, the 2002 Highway Diesel Progress Review and the recently released Highway Diesel Progress Review Report 2.35,36,37,38 The following sections summarize the challenges to applying these technologies to nonroad engines and why we believe the emission standards finalized today are technically feasible in the leadtime provided.

1. Can Advanced Diesel Emission Control Technologies Be Applied to Nonroad Engines and Equipment?

The emission standards and the introduction dates for those standards, as described earlier in this section, are premised on the transfer of diesel engine technologies being or already developed to meet light duty and heavy duty vehicle standards that begin in 2007. The advanced technology standards that we are finalizing today for engines over 25 horsepower will begin to go into effect four years later. This time lag between equivalent highway and nonroad diesel engine standards is necessary in order to allow time for engine and equipment manufacturers to further develop these highway technologies for nonroad engines and to align this program with nonroad Tier 3 emission standards that begin to go into effect in 2006.

This section summarizes the engineering challenges to applying advanced emission control technologies to nonroad engines and equipment, and why we believe that technologies developed for highway diesel engines can be further refined to address these issues in a timely manner for nonroad engines consistent with the emission standards finalized today. 57 a. Nonroad Operating Conditions and Exhaust Temperatures Nonroad equipment is highly diverse in design, application, and typical operating conditions. This variety of operating conditions affects emission control systems through the resulting variety in the torque and speed demands ( i. e., power demands). In our proposal, we highlighted the challenge for design and implementation of advanced emission control technologies posed by this wide range in what constitutes typical nonroad operation. Some commenters emphasized their concerns regarding this issue as well, and their belief that these issues make the application of the technology to nonroad infeasible. While we recognize and agree with the commenters regarding the nature of the challenges, we disagree with their conclusion regarding feasibility because, as described in the following section, we see a clear path to overcome the challenges.

The primary concern for catalyst based emission control technologies is exhaust temperature. In general, exhaust temperature increases with engine power and can vary dramatically as engine power demands vary. For catalyzed diesel particulate filters ( CDPFs), exhaust temperature determines the rate of filter regeneration, and if too low, causes a need for supplemental means to ensure proper filter regeneration. In the case of the CDPF, it is the aggregate soot regeneration rate that is important, not the regeneration rate at any particular moment in time. A CDPF controls PM emissions under all conditions and can function properly ( i. e., not plug) even when exhaust temperatures are low for an extended time and the regeneration rate is lower than the soot accumulation rate, provided that occasionally exhaust temperatures and thus the soot regeneration rate are increased enough to regenerate the CDPF. Similarly, there is a minimum temperature ( e. g., 200 ° C) for NO X adsorbers below which NO X regeneration is not readily possible and a maximum temperature ( e. g., 500 ° C) above which NO X adsorbers are unable to effectively store NO X. Therefore, there is a need to match diesel exhaust temperatures to conditions for effective catalyst operation under the various operating conditions of nonroad engines.

Although the range of products for highway vehicles is not as diverse as for nonroad equipment, the need to match exhaust temperatures to catalyst characteristics is still present. This is an important concern for highway engine manufacturers and has been a focus of our ongoing 2007 diesel engine progress review. There we have learned that substantial progress is being made to broaden the operating temperature window of catalyst technologies while at the same time to design engine systems to better control average exhaust temperatures ( for ongoing catalyst performance) and to attain periodically higher temperatures ( to control PM filter regeneration and NO X adsorber desulfation). Highway diesel engine manufacturers are working to address this need through modifications to engine design, modifications to engine control strategies, and modifications to exhaust system designs. New engine control strategies designed to take advantage of engine and exhaust system modifications can be used to manage exhaust temperatures across a broad range of engine operation. The technology solutions being developed for highway engines to better manage exhaust temperature are built upon the same emission control technologies ( i. e., advanced air handling systems and electronic fuel injection 39 Sasaki, S., Ito, T., and Iguchi, S., " Smoke less Rich Combustion by Low Temperature Oxidation in Diesel Engines," 9th Aachener Kolloquim Fahrzeug  und Motorentechnik 2000. Copy available in EPA Air Docket A 2001 28 Item II A 56.

40 Jeuland, N., et al, " Performances and Durability of DPF ( Diesel Particulate Filter) Tested on a Fleet of Peugeot 607 Taxis First and Second Test Phases Results," October 2002, SAE 2002 01 2790.

58 systems) that we expect nonroad engine manufacturers to use in order to comply with the existing Tier 3 emission standards.

Matching the emission control technology and the operating temperature window of the broad range of nonroad equipment may be somewhat more challenging for nonroad engines than for many highway diesel engines simply because of the diversity in equipment design and equipment use. Nonetheless, the problem has been successfully solved in highway applications facing low exhaust temperature performance situations as difficult to address as any encountered by nonroad applications. The most challenging temperature regime for highway engines are encountered at very light loads as typified by congested urban driving with periods of extended idle operation. Under congested urban driving conditions, exhaust temperatures may be too low for effective NO X reduction with a NO X adsorber catalyst. Similarly, exhaust temperatures may be too low to ensure passive CDPF regeneration. To address these concerns, light duty diesel engine manufacturers have developed active temperature management strategies that provide effective emissions control even under these difficult light load conditions. Toyota has shown with their prototype diesel particulate NO X reduction ( DPNR) vehicles that changes to EGR and fuel injection strategies can realize an increase in exhaust temperatures of more than 100 ° F under even very light load conditions allowing the NO X adsorber catalyst to function under these normally cold exhaust conditions. 39 Similarly, PSA Peugeot Citroen ( PSA) has demonstrated effective CDPF regeneration under demanding light load taxi cab conditions with current production technologies. 40 Both of these are examples of technology paths available to nonroad engine manufacturers to increase temperatures under light load conditions.

While a number of commenters expressed concerns about low temperature operation for nonroad equipment, no commenters provided data showing that nonroad equipment in use operating cycles would be more demanding of low temperature performance than passenger car urban driving. Both the Toyota and PSA systems are designed to function even with extended idle operation as would be typified by a taxi waiting to pick up a fare.

It is our conclusion that by actively managing exhaust temperatures, for example through engine management to increase exhaust temperatures, engine manufacturers can ensure highly effective catalyst based emission control performance ( i. e., compliance with the emission standards across the applicable tests) and reliable filter regeneration across a wide range of engine operation as would be typified by the broad range of in use nonroad duty cycles. Active methods of regenerating PM filters have been shown to be reliable under all operating conditions and can 41 We do not have Tier 3 emission standards for engines in the horsepower category from 25 50 hp. However, we expect that similar Tier 3 emission control technologies will form part of the emission control technology package used for compliance with the Tier 4 standards for these engines in 2013. Our cost analysis reflects the additional cost to apply these technologies for NOX and PM control.

59 be applied to nonroad diesel engines in the time frame required by these regulations. The additional cost for active regeneration, beyond the cost for the PM filter alone, has been accounted for in the cost analysis summarized in section VI of this preamble.

We have conducted an analysis of various nonroad equipment operating cycles and various nonroad engine power density levels to better understand the matching of nonroad engine exhaust temperatures, catalyst installation locations and catalyst technologies. This analysis, documented in the RIA, shows that for many engine power density levels and equipment operating cycles, exhaust temperatures are quite well matched to catalyst temperature window characteristics. In particular, the nonroad transient cycle ( NRTC), the cycle we are finalizing to use for certification for most engines with rated power less than 750 hp, was shown to be well matched to the NO X adsorber characteristics with estimated performance in excess of 90 percent for a turbocharged diesel engine tested under a range of power density levels. The analysis also indicated that the exhaust temperatures experienced over the NRTC are better matched to the NO X adsorber catalyst temperature window than the temperatures that would be expected over the highway FTP test cycle. This suggests ( when coupled with the fact that PM filters function with equal effectiveness at essentially all conditions) that compliance based on testing with the nonroad Tier 4 standards on the NRTC will be somewhat easier, using similar technology, than complying with the highway 2007 emission standards on the highway transient test cycle.

In sum, we believe based on our analysis of nonroad engines and equipment operating characteristics, that, in use, some nonroad engines will experience conditions that require the use of temperature management strategies ( e. g., active regeneration) in order to effectively use the NO X adsorber and CDPF systems. We have assumed in our cost analysis that all nonroad engines complying with a PM standard of 0.03 g/ bhp hr or lower will have an active means to control temperature ( i. e. we have costed a backup regeneration system, although some applications likely may not need one). We have made this assumption believing, as indicated by a number of commenters, that manufacturers will not be able to accurately predict in use conditions for every piece of equipment and will thus choose to provide the technologies on a back up basis. As explained earlier, the technologies necessary to accomplish this temperature management are enhancements of both the Tier 3 emission control technologies that will form the starting point for Tier 4 engines larger than 50 hp, and the control strategies being developed for highway diesel engines. 41 Based on our analyses, we believe that there are no nonroad engine applications above 25 horsepower for which these highway engine approaches for temperature management will not work. However, we agree with commenters that given the diversity in nonroad equipment design and application, additional time will be needed in order to match the engine performance characteristics to the full range of nonroad equipment. 42 " Summary of Conference Call between U. S. EPA and Deutz Corporation on September 19,

2002 regarding Deutz Diesel Particulate Filter System", EPA Memorandum to Air Docket A 2001 28 60 We have concluded that, given the timing of the emissions standards finalized today, and the availability and continuing development of technologies to address temperature management for highway engines which technologies are transferrable to all nonroad engines with greater than 25 hp power rating, nonroad engines can be designed to meet the new standards in the lead time provided, and can be provided to equipment makers in a timely manner within that lead time.

b. Nonroad Operating Conditions and Durability Nonroad equipment is designed to be used in a wide range of tasks, from mining equipment to crop cultivation and harvesting to excavation and loading, and operated in harsh environments. In the normal course of equipment operation the engine and its associated hardware will experience levels of vibration, impacts, and dust that may exceed conditions typical of highway diesel vehicles. For this reason, some commenters said that the PM filter technology was infeasible for nonroad equipment. We disagree with this assertion and continue to believe that PM filter technologies can be applied to a wide range of nonroad equipment.

Specific efforts to design for the nonroad operating conditions will be required in order to ensure that the benefits of these new emission control technologies are realized for the life of nonroad equipment. Much of the engineering knowledge and experience to address these issues already exists with the nonroad equipment manufacturers. Vibration and impact issues are fundamentally mechanical durability concerns ( rather than issues of technical feasibility of achieving emissions reductions) for any component mounted on a piece of equipment ( e. g., an engine coolant overflow tank). Equipment manufacturers must design mounting hardware such as flanges, brackets, and bolts to support the new component without failure. Further, the catalyst substrate material itself must be able to withstand the conditions encountered on nonroad equipment without itself cracking or failing. There is a large body of real world testing with retrofit emission control technologies on engines up to 750 hp that demonstrate the durability of the catalyst components themselves even in the harshest of nonroad equipment applications. The evidence for even larger engines ( i. e., those above 750 hp) is less conclusive because of the limited number of applications.

Deutz, a nonroad engine manufacturer, sold approximately 2,000 diesel particulate filter systems for nonroad equipment in the period from 1994 through 2000. The very largest of these systems were limited to engine sizes below 850 hp. The majority of these systems were sold into significantly smaller applications. Many of these systems were sold for use in mining equipment. Mining equipment is exposed to extraordinarily high levels of vibration, experiences impacts with the mine walls and face, and encounters high levels of dust. Yet in meetings with the Agency, Deutz shared their experience that no system had failed due to mechanical failure of the catalyst or catalyst housing. 42 The Deutz system utilized a conventional cordierite PM filter substrate as is Item II B 31.

61 commonly used for heavy duty highway truck CDPF systems. The canning and mounting of the system was a Deutz design. Deutz was able to design the catalyst housing and mounting in such a way as to protect the catalyst from the harsh environment as evidenced by its excellent record of reliable function.

A number of commenters asserted that it was not possible to apply conventional CDPF technologies ( i. e., ceramic wall flow filter media) to the largest diesel engines with power ratings above 750 hp. In the draft RIA for the proposal, we described our expectation that these highway based systems could be assembled into larger systems to work well for these largest diesel engines. While we continue to believe that it may be possible in the time frame of this rulemaking for these conventional CDPFs to be applied to engines with more than 750 hp, based on the evidence provided by the commenters, we now agree that too much uncertainty remains for us to reach that conclusion today. We cannot clearly today describe a method to monitor the soot loading of individual filter elements in a parallel system made up of a significant number of smaller components. This is because for parallel systems the pressure drop ( the best current method to monitor filter condition) across all of the parallel components is exactly the same. If a single filter begins to plug and needs to be regenerated it may not be detected in such a system. Therefore, we believe that instead of a massively parallel filter system, an alternate PM filtering media may be more appropriate in order to address issues of scalability, durability and packaging for these largest engines. Fortunately, there are other filter media technologies ( e. g., wire or fiber mesh depth filters) that can be successfully scaled to any size and which we have confidence in projecting today will be a more appropriate solution for the bulk of the engines in this size category. Because these depth filtration technologies are not quite as efficient at filtering PM as the ceramic systems that are the dominant solution for the smaller highway diesel engines, we are finalizing a set of PM filter based standards for engines greater than 750 hp which are slightly higher than the proposed PM standards for these engines. Those standards are discussed in sections II. A and II. B. 3 below. Our cost estimates summarized in section VI for engines greater than 750 hp are consistent with the use of either silicon carbide or wire mesh PM filter technologies.

Certain nonroad applications, including some forms of harvesting equipment, consumer lawn and garden equipment, and mining equipment, may have specific limits on maximum surface temperature for equipment components in order to ensure that the components do not serve as ignition sources for flammable dust particles ( e. g. coal dust or fine crop/ lawn dust). Some commenters have raised concerns that these design constraints might limit the equipment manufacturers ability to install advanced diesel catalyst technologies such as NO X adsorbers and CDPFs. This concern seems to be largely based upon anecdotal experience with gasoline catalyst technologies where under certain circumstances catalyst temperatures can exceed 1,000 ° C and without appropriate design considerations could conceivably serve as an ignition source. We do not believe that these concerns are justified in the case of either the NO X adsorber catalyst or the CDPF technology. Catalyst temperatures for NO X adsorbers and CDPFs should not exceed the 43 The hottest surface on a diesel engine is typically the exhaust manifold which connects the engines exhaust ports to the inlet of the turbocharger. The hot exhaust gases leave the engine at a very high temperature ( 800 ° C at high power conditions) and then pass through the turbocharger where the gases expand driving the turbocharger providing work. The process of extracting work from the hot gases cools the exhaust gases. The exhaust leaving the turbocharger and entering the catalyst and the remaining pieces of the exhaust system is cooler ( as much as 200 ° C at very high loads) than in the exhaust manifold.

44 " Engine Technology and Application Aspects for Earthmoving Machines and Mobile Cranes, Dr. E. Brucker, Liebherr Machines Bulle, SA, AVL International Commercial Powertrain Conference, October 2001. Copy available in EPA Air Docket A 2001 28, Docket Item # II A 12.

62 maximum exhaust manifold temperatures already commonly experienced by diesel engines ( i. e, catalyst temperatures are expected to be below 800 ° C). 43 CDPF temperatures are not expected to exceed approximately 700 ° C in normal use and are expected to only reach the 650 ° C temperature during periods of active regeneration. Similarly, NO X adsorber catalyst temperatures are not expected to exceed 700 ° C and again only during periods of active sulfur regeneration as described in section III. C below. Under conditions where diesel exhaust temperatures are naturally as high as 650 ° C, no supplemental heat addition from the emission control system will be necessary for regeneration and therefore exhaust temperatures will not exceed their natural level. When natural exhaust temperatures are too low for effective emission system regeneration then supplemental heating, as described earlier, may be necessary but would not be expected to produce temperatures higher than the maximum levels normally encountered in diesel exhaust. Furthermore, even if it were necessary to raise exhaust temperatures to a higher level in order to promote effective emission control, there are technologies available to isolate the higher exhaust temperatures from flammable materials such as dust. One approach would be the use of airgapped exhaust systems ( i. e., an exhaust pipe inside another concentric exhaust pipe separated by an air gap) that serve to insulate the inner high temperature surface from the outer surface which could come into contact with the dust. The use of such a system also may be desirable in order to maintain higher exhaust temperatures inside the catalyst in order to promote better catalyst function. Another technology to control surface temperature already used by some nonroad equipment manufacturers is water cooled exhaust systems. 44 This approach is similar to the airgapped system but uses engine coolant water to actively cool the exhaust system.

We thus do not believe that flammable dust concerns will prevent the use of either a NO X adsorber or a CDPF because catalyst temperatures are not expected to be unacceptably high and because remediation technologies exist to address these concerns. In fact, exhaust emission control technologies ( i. e., aftertreatment) have already been applied on both an original equipment manufacturer ( OEM) basis and for retrofit to nonroad equipment for use in potentially explosive environments. Many of these applications must undergo Underwriters Laboratory ( UL) approval 45 Phone conversation between Byron Bunker, United States Environmental Protection Agency and Dale McKinnon, Manufacturers of Emission Control Association ( MECA), 9 April, 2003 confirming the use of emission control technologies on nonroad equipment used in coal mines, refineries, and other locations where explosion proofing may be required.

46 As an alternative to compliance with the ISO C1 test procedure, a manufacturer can show compliance with the standards by testing over the Ramped Modal Cycle ( RMC) as described in section III. F.

63 before they can be used. 45 Therefore, while we appreciate the commenters' concerns regarding safety, we remain convinced that the application of these emission control technologies will not compromise ( or decrease) equipment safety.

We agree that nonroad equipment must be designed to address safety and durable performance for a wide range of operating conditions and applications that would not commonly be experienced by highway vehicles. We believe further as demonstrated by retrofit experiences around the world that technical solutions exist which allow catalyst based emission control technologies to be applied to nonroad equipment.

2. Are the Standards for Engines 75   750 hp feasible?

There are three primary test provisions and associated standards in the Tier 4 program we are finalizing today. These are the Nonroad Transient Cycle ( NRTC), the existing International Organization for Standardization ( ISO) C1 steady state cycle, and the highway based Not To Exceed ( NTE) provisions. 46 Under today's rules, most nonroad diesel engines must meet the new standards for each of these three test cycles ( the exceptions are noted below). Compliance on the transient test cycle includes weighting the results from a cold start and hot start test with the cold start emissions weighted at 1/ 20 and hot start emissions weighted at 19/ 20. Additionally, we have alternative optional test cycles including the existing ISO D2 steady state cycle and the Transportation Refrigeration Unit ( TRU) cycle which a manufacturer can choose to use for certification in lieu of the NRTC and the ISO C1, provided that the manufacturer can demonstrate to the Agency that the engine will only be used in a limited range of nonroad equipment with known operating conditions. A complete discussion of these various test cycles can be found in chapter 4.2, 4.3, and 4.4 of the RIA.

The standards we are finalizing today for nonroad engines with rated power from 75 to 750 hp are based upon the performance of technologies and standards for highway diesel engines which go into effect in 2007. As explained above, we believe these technologies, namely NO X adsorbers and catalyzed diesel particulate filters enabled by 15 ppm sulfur diesel fuel, can be applied to nonroad diesel engines in a similar manner as for highway diesel engines. The combustion process and the means to modify that process are fundamentally the same for highway and nonroad diesel engines regardless of engine size. The formation mechanism and quantity of 64 pollutants formed in diesel engines are fundamental characteristics of engine design and are not inherently different for highway and nonroad engines regardless of engine size. The effectiveness of NO X adsorbers to control NO X emissions and CDPFs to control PM, NMHC, and CO emissions are determined by fundamental catalyst and filter characteristics. Therefore, we disagree with commenters who suggest that these highway technology based emission standards are infeasible for nonroad engines. We acknowledge the comments raised regarding the unique characteristics nonroad diesel engines which must be considered in setting these standards, and we have addressed those issues by allowing ( where appropriate) for additional lead time or slightly less stringent standards for nonroad diesel engines in comparison to highway diesel engines ( and likewise have made appropriate cost estimates to account for the technology and engineering needed to address these issues).

PM Standard We are finalizing a PM standard for engines in this category of 0.01 g/ bhp hr based upon the emissions reductions possible through the application of a CDPF and 15ppm sulfur diesel fuel. This is the same emissions level as for highway diesel engines in the heavy duty 2007( HD2007) program ( 66 FR 5001, January 18, 2001). While emission levels of engine out soot ( the solid carbon fraction of PM) may be somewhat higher for some nonroad engines when compared to highway engines, these emissions are virtually eliminated ( reduced by 99 percent) by the CDPF technology. With application of the CDPF technology, the soluble organic fraction ( SOF) portion of diesel PM is predicted to be all but eliminated. The primary emissions from a CDPF equipped engine are sulfate PM emissions formed from sulfur in diesel fuel. The emissions rate for sulfate PM is determined primarily by the sulfur level of the diesel fuel and the rate of fuel consumption. With the 15 ppm sulfur diesel fuel, the PM emissions level from a CDPF equipped nonroad diesel engine will be similar to the emissions rate of a comparable highway diesel engine. Therefore, the 0.01 g/ bhp hr emission level is feasible for nonroad engines tested on the NRTC cycle and on the steady state cycles, ISO C1 and ISO D2. Put another way, control of PM using CDPF technology is essentially independent of duty cycle given active catalyst technology ( for reliable regeneration and SOF oxidation), adequate control of temperature ( for reliable regeneration) and low sulfur diesel fuel ( for reliable regeneration and low PM emissions). While some commenters argued that PM filters will not enable the 0.01 PM emission standard for nonroad engines, we remain convinced by the demonstration of 0.01 or lower PM emission levels from a number of diesel engines described in the RIA, that the standard is feasible given the leadtime provided and the availability of 15 ppm sulfur diesel fuel. Likewise, the NTE provisions for nonroad engines are the same as for on highway engines meeting an equivalent PM control level. The maximum PM emission level from a CDPF equipped diesel engine is primarily determined by the maximum fuel sulfur conversion level experienced at the highest operating conditions. As documented in RIA chapter <IP_ADDRESS>, testing of diesel engines at conditions representative of the highest sulfate PM formation rates shows PM levels below the level required by the NTE provisions when tested on less than 15 ppm sulfur diesel fuel.

NO X Standard 47 For engines between 75 and 100 horsepower, this may require re optimization of the engine to lower NOX emissions if they are higher than 3.0, but we would not expect any new hardware beyond the Tier 3 hardware to be required in the Tier 4 timeframe to accomplish this reduction.

65 We are finalizing a NO X standard of 0.30 g/ bhp hr for engines in this category based upon the emission reductions possible from the application of NO X adsorber catalysts and the expected emission levels for Tier 3 compliant engines which form the baseline technology for Tier 4 engines. The Tier 3 emission standards are a combined NMHC+ NO X standard of 3.0 g/ bhp hr for engines greater than 100 hp and less than 750 horsepower. For engines less than 100 hp but greater than 50 horsepower the Tier 3 NMHC+ NO X emission standard is 3.5 g/ bhp hr. We believe that in the time frame of the Tier 4 emission standards, all engines from 75 to 750 hp can be developed to control NO X emissions to engine out levels of 3.0 g/ bhp hr or lower. 47 This means that all engines will need to apply Tier 3 emission control technologies ( i. e., turbochargers, charge air coolers, electronic fuel systems, and for some manufacturers EGR systems) to get to this baseline level. As discussed in more detail in the RIA, our analysis of the NRTC and the ISOC1 cycles indicates that the NO X adsorber catalyst can provide a 90 percent or greater NO X reduction level on the cycles. The standard of 0.30 g/ bhp hr reflects a baseline emissions level of 3.0 g/ bhp hr and a greater than 90 percent reduction of NO X emissions through the application of the NO X adsorber catalyst. The additional lead time available to nonroad engine manufacturers and the substantial learning that will be realized from the introduction of these same technologies to highway diesel engines, plus the lack of any fundamental technical impediment, makes us confident that the new NO X standards can be met.

Given the fundamental similarities between highway and nonroad diesel engines, we believe that the NO X adsorber technology developed for highway engines can be applied with equal effectiveness to nonroad diesel engines with additional developments in engine thermal management ( as discussed in section II. B. 2 above) to address the more widely varied nonroad operating cycles. In fact, as discussed previously, the NO X adsorber catalyst temperature window is particularly well matched to transient operating conditions as typified by the NRTC.

As pointed out by some commenters, compliance with the NTE provisions will be challenging for the nonroad engine industry due to the diversity of nonroad products and operating cycles. However, the technical challenge is reduced somewhat by the 1.5 multiplier used to calculate the NTE standard as discussed in section III. J. Controlling NO X emissions under NTE conditions is fundamentally similar for both highway and nonroad engines. The range of control is the same and the amount of reduction required is also the same. We know of no technical impediment, nor were any raised by commenters, that would prevent achieving the NTE standard under the zone of operating conditions required by the NTE.

NMHC Standard 48 " The Impact of Sulfur in Diesel Fuel on Catalyst Emission Control Technology," report by the Manufacturers of Emission Controls Association, March 15, 1999, pp. 9 & 11. Copy available in EPA Air Docket A 2001 28 Item II A 67.

66 Meeting the NMHC standard under the lean operating conditions typical of the biggest portion of NO X adsorber operation should not present any special challenges to nonroad diesel engine manufacturers. Since CDPFs and NO X adsorbers contain platinum and other precious metals to oxidize NO to NO 2, they are also very efficient oxidizers of hydrocarbons. NMHC reductions of greater than 95 percent have been shown over transient and steady state test procedures. 48 Given that typical engine out NMHC is expected to be in the 0.40 g/ bhp hr range or lower for engines meeting the Tier 3 standards, this level of NMHC reduction will mean that under lean conditions emission levels will be well below the standard. For the same reasons, there is no obstacle which would prevent achieving the NTE standard.

Under the brief episodic periods of rich operation necessary to regenerate NO X adsorber catalysts, it is possible to briefly experience higher levels of NMHC emissions. Absent a controlling standard, it is possible that these NMHC emissions could be high. There are two possible means to control the NMHC emissions during these periods in order to meet the NMHC standard finalized today. Manufacturers can design the regeneration system and the oxygen storage ( oxidation function under rich conditions) of the NO X adsorber catalyst such that the NMHC emissions are inherently controlled. This is similar to the control realized on today's three way automotive catalysts which also experience operation that toggles between rich and lean conditions. Secondly, a downstream clean up catalyst can be used to oxidize the excess NMHC emissions to a level below the standard. This approach has been used in the NO X adsorber demonstration program at EPA described in the RIA. Our cost analysis for engines in the 75 to 750 hp category includes a cost for a clean up catalyst to perform this function.

Cold Start The standards include a cold start provision for the NRTC procedure. This means that the results of a cold start transient test will be weighted with the emissions of a hot start test in order to calculate the emissions for compliance against the standards. In a change from the proposed rule, the weightings are 1/ 20 cold start and 19/ 20 for the hot start ( as opposed to the proposed weightings of 1/ 10 and 9/ 10, respectively) as described more fully in chapter 4.2 of the RIA and section III. F below. Because exhaust temperatures are so important to catalyst performance, a cold start provision is an important tool to ensure that the emissions realized in use are consistent with the expectations of this program. Achieving this standard represents an additional technical challenge for NO X control and to a lesser extent CO and NMHC control ( i. e., control of gaseous pollutants). PM control with a CDPF is not expected to be significantly impacted by cold start provisions due to the primary filter mechanism being largely unaffected by temperature. 49 The combined weighted average performance is calculated as 1/ 20 ( cold start) + 19/ 20 (

hotstart Hence it can be seen that 1/ 20 ( 70%) + 19/ 20 ( 91%) = 90% and likewise that 1/ 20 ( 50%) + 19/ 20 67 With respect to achievability of the NO X, CO and NMHC standards, during the initial start and warmup period for a diesel engine, the exhaust temperatures are typically below the light off temperature of a catalyst. As a result, exhaust stack emissions may initially be higher during this period of operation. The cold start test procedure is designed to quantify these emissions to ensure that emission control systems are designed appropriately to minimize the contribution of cold start emissions. Cold start emissions can be minimized by improving catalyst technology to allow for control at lower exhaust temperatures ( i. e., by lowering the catalyst light off temperature) and by applying strategies to quickly raise the exhaust temperature to a level above the catalyst light off temperature.

There are number of technologies available to the engine manufacturer to promote rapid warmup of the exhaust and emission control system. These include retarding injection timing, increasing EGR, and potentially late cycle injection, all of which are technologies we expect manufacturers to apply as part of the normal operation of the NO X adsorber catalyst system. These are the same technologies we expect highway engine manufacturers to use in order to comply with the highway cold start FTP provision which weights cold start emissions more heavily with a 1/ 7 weighting. As a result, we expect the transfer of highway technology to be well matched to accomplish this control need for nonroad engines as well. Using these technologies we expect nonroad engine manufacturers to be able to comply with the new Tier 4 NO X, CO, and NMHC emission standards including the cold start provisions of the transient test procedure.

One commenter has raised the concern that if diesel engines are no cleaner than 3 g/ bhp hr NO X and if NO X adsorbers can be no more efficient than 90 percent, then any increase in NO X emissions above the 0.30 g/ bhp hr level on a cold start test will make the emission standards infeasible. We should clarify, when discussing the emission reduction potential of the NO X adsorber catalyst generically in the NPRM, we have sometimes simply stated that it is 90 percent or more effective without plainly saying that this refers to our expectation for average performance considering both cold and hot start emissions. More precisely then, we would expect lower effectiveness over the cold start test procedure with somewhat higher effectiveness realized over the hot start test procedure. Because of the relative weightings of the two test cycles ( i. e., 1/ 20 for the cold start and 19/ 20 for the hot start), although the degradation of performance below 90 percent over the cold start cycle can be substantially greater than the performance above 90 percent realized over the hot start cycle, the standards remain feasible. For example, even if the average NO X adsorber performance over the cold start test cycle was only 70 percent, the average NO X adsorber performance over the hot start portion of the test cycle would only need to be 91 percent in order to realize a weighted average performance of 90 percent. Similarly, were the cold start test cycle performance only 50 percent, the hot start performance would only need to be 92 percent in order to realize a weighted average performance of 90 percent. 49 We are confident, based on our estimates of NO X adsorber performance over the ( 92%) = 90%.

68 nonroad test cycle summarized in the RIA, that NO X adsorber performance in excess of 92 percent can be expected in the time frame of the requirements finalized today.

Complying with the PM standard given consideration of the cold start test procedure is not expected to be as challenging as compliance with the NO X standard. The effectiveness for PM filtration is not significantly effected by exhaust temperatures, as noted earlier. Thus, PM emission levels are similar over the cold and hot start tests.

The standards that we are finalizing today for nonroad engines with rated horsepower levels from 75 to 750 hp are based upon the same emission control technologies, clean 15ppm or lower sulfur diesel fuel, and relative levels of emission control effectiveness as the HD 2007 emission standards. We have given consideration to the diversity of nonroad equipment for which these technologies must be developed and the timing of the Tier 3 emissions standards in determining the appropriate timing for the Tier 4 standards. Based upon the availability of the emission control technologies, the proven effectiveness of the technologies to control diesel emissions to these levels, the technology paths identified here to address constraints specific to nonroad equipment, and the additional lead time afforded by the timing of the standards, we have concluded that the standards are technically feasible in the leadtime provided.

3. Are the Standards for Engines above 750 hp Feasible?

The preceding discussion of the standards for engines of 75 to 750 hp highlights the main thrust of our new Tier 4 program, a focus on realizing very low on highway like emission levels for the vast majority of nonroad diesel engines. The emission standards and the combination of technologies that we expect will be used to meet those standards are virtually identical to the HD2007 program for on highway engines. The following three sections ( II. B. 3, II. B. 4, and II. B. 5) describing the feasibility of the standards for engines above 750 hp, from 25 to 75 hp, and below 25 hp, while following the same pattern and objective, take additional consideration of the fact that engines and equipment in these size categories have no direct on highway equivalent and differ from highway engines in substantial ways that cause us to reach differing conclusions regarding the appropriate standards and timing for those standards. Whether in scale, or use, or operating conditions, the characteristics of these engines and equipment are such that we have taken particular consideration of them in setting the timing and level of the standards. The remainder of this section ( II. B. 3) discusses what makes the above 750 hp category unique and why the standards which we are adopting are technologically feasible.

a. What makes the over 750 hp category different?

The first and most obvious difference for engines in this horsepower category is scale. No on highway engines come close to the size of the largest engines in this category which can produce in excess of 3,000 horsepower, consist of 16 or more cylinders and have 12 or more 69 turbochargers. The engines, and the equipment that they power, are quite simply significantly larger than any on highway diesel engine. Many commenters argued that emission technologies from on highway vehicles could not be simply scaled up for these larger engines and that if they were, the consequences of this resizing would include structural weakness and reduced system robustness. As discussed below, our review of the information provided with these comments and our subsequent analysis of the technical characteristics of some emission control components has led us to conclude that revised emission standards ( based on performance of different technologies that those whose performance formed the basis for the proposed rule) from those we proposed for this horsepower category are appropriate and available.

We have concluded that it is appropriate to distinguish between two broad categories of engines over 750 hp grouped by application: mobile machines and generator sets. Mobile machines include the very largest nonroad equipment used in mining trucks and large excavation equipment. The environment and operating conditions ( especially for vibration) represent the harshest application into which nonroad engines are applied. Design considerations for technologies used to control emissions from engines in these applications must first consider robustness to the harsh environments that will be experienced in use. In contrast, mobile nonroad generator sets operate in relatively good operating environments. In addition, while mobile nonroad generator sets can, and are moved between operating locations, they are always stationary during actual operation. Thus the levels of vibration and the general environment for engine operation are significantly less demanding for generator sets than for mobile machines. Also the dynamic range of operation is significantly narrower and less demanding for generator sets. Designed to operate at a set engine speed, synchronous to the frequency cycle desired for electric generation ( i. e., 1200 or 1800 RPM for 60hz), diesel engines designed for generator set applications can be optimized for operation in this narrow range.

We have given specific consideration to the unique engineering challenges for engines in this horsepower category in determining the appropriate emission standards set in today's action. We have also taken into account the important differences between generator set applications and other mobile applications in developing standards for this horsepower category.

b. Are the new Tier 4 standards for over 750 hp engines technologically feasible?

The emission standards described in section II. A above describe a comprehensive program for engines over 750 hp that give consideration to both the physical size of these engines and the applications into which these engines are applied. Engines in this power category must show compliance with the C1 or D2 steady state test cycles as appropriate as well as with the NTE provisions finalized today. As described in sections III. F and III. G, these engines will not be tested over the NRTC nor will they be subject to a cold start test procedure. The feasibility discussion in this section describes expected performance of the engines over the required test cycles and the NTE. This section will briefly summarize the feasibility analysis contained in the RIA for these engines. 70 PM Standards Beginning in 2011 all nonroad diesel engines above 750 hp must meet a PM standard of 0.075 g/ bhp hr. We believe that this PM standard is feasible based on the substantial reductions in sulfate PM due to the use of 15 ppm sulfur diesel fuel and the potential to improve the combustion process to reduce PM emissions formed in the engine. Specifically, we believe based on the evidence in the RIA that increasing fuel injection pressure, improving electronic controls and optimizing the combustion system geometry will allow engine manufacturers to meet this level of PM control in 2011. Some engine manufacturers have in fact indicated to the Agency that this level of control represents an achievable goal by 2011. One commenter argued however, that a more relaxed standard of 0.1 g/ bhp hr based on today's on highway diesel engine performance would be appropriate. We disagree with this comment, believing that given the substantial leadtime available and the potential for further improvements in combustion systems, that it is appropriate to set a forward looking PM standard of 0.075 g/ bhp hr. Conversely, other commenters argued that future on highway PM filter technology should be applied to this class of engines as early as 2011 ( i. e., that a standard of 0.01 g/ bhp hr PM is appropriate). While we agree with the commenters that in the long term it will be appropriate to apply filter based emission control technologies to these engines, we do not agree that such control is appropriate as early as 2011. As the following section explains, we believe that there are remaining technical challenges to be addressed prior to the application of PM filters to these engines and that it is necessary to allow additional leadtime for those challenges to be addressed.

Beginning in 2015 all nonroad engines over 750 hp must meet stringent PM filter technology based emission standards of 0.02 g/ bhp hr for engines used in generator set applications and 0.03 g/ bhp hr for engines used in mobile machine applications. We are predicating these emission standards based on the application of a different form of diesel particulate filter technology, a wire or fiber mesh depth filter rather than a ceramic wall flow filter. Wire mesh filters are capable of reducing PM by 70 percent or more. We have not based these standards upon the more efficient (> 90 percent) control possible from ceramic wall flow style PM filters, because we believe that the application of the wall flow filter technology on engines of this size has not been adequately demonstrated at this time. While it would certainly be possible to apply the ceramic based technology to these larger engines, we cannot today conclude with certainty that such systems would be as robust in use as needed ( see earlier discussion in section II. B. 1. b). Considering the information available to the Agency today, we believe it appropriate to set the long term PM standard for these very large engines based on technologies which we can project with confidence will give high levels of emission reduction, durability, and robustness when scaled to these very large engine sizes.

The 0.01 g/ bhp hr difference in the PM emission standards between the standard for generator sets and for other mobile applications in this category ( 0.01 g/ bhp hr lower for generator sets) reflects our expectation that engine out emissions from generator sets can be reduced below the level for mobile machines due to generator set operation at a single engine speed. Without the need to provide full power and control over the wider range of possible 71 operating conditions that mobile machines must deliver, we believe that the air handling systems ( especially the turbocharger match to the engine) can be improved to provide a moderate reduction in engine out emissions. This, coupled with the reduction afforded by the PM filter technology, would allow generator sets to meet a more stringent 0.02 g/ bhp hr standard. Diesel engines designed for use in generator sets meeting this standard will need to demonstrate compliance over the appropriate test cycles, either the ISO C1 or D2 tests. As discussed in RIA chapter <IP_ADDRESS>, PM emission rates are nearly the same for steady state testing or for alternative ramped modal cycle ( RMC) testing. These test cycles, like the engines, are designed to be representative of the range of operation expected from a generator set.

As discussed previously, PM emission control over the NTE region for PM filter equipped diesel engines is predominantly a function of sulfate formation at high exhaust temperatures. Given that fuel consumption ( and thus sulfur) consumption rates on a brake specific basis tend to be lower for engines above 750hp, we can conclude that the increase in PM emissions over the NTE region will likely be lower for these engines than for engines meeting the 0.01 g/ bhp hr standard. Thus, we can conclude based on the evidence in the RIA that compliance with the NTE provisions for PM is feasible for engines over 750 hp.

Although we are projecting that manufacturers will comply with this standard using a slightly less efficient PM filter technology, we remain convinced that 15 ppm sulfur diesel fuel will still be a necessity for this technology to be applied. Regardless of the filter media chosen for the PM filter, the filter will still require catalyst based systems to ensure robust regeneration and adequate control of the SOF portion of PM. As these catalyst based technologies are adversely impacted by sulfur in diesel fuel as described in II. C below, 15 ppm sulfur diesel fuel will be required in order to ensure compliance with the PM standards finalized here for engines over 750 hp.

NO X Standards As with the PM standards, we are setting distinct NO X standards for this category of engines reflecting particular concerns with the application of technologies to engines of this size and our desire to realize significant NO X reductions as soon as possible. There are two sets of NO X standards that we are finalizing today, a 0.50 g/ bhp hr NO X standard for engines used in generator set applications and a 2.6 g/ bhp hr NO X standard for mobile machines.

For engines used in generator set applications we are finalizing a 0.50 g/ bhp hr standard that goes into effect for engines above 1,200 hp in 2011 and in 2015 for engines above 750 hp. We see two possible technology options for manufacturers to meet these standards. First, compliance with this NO X standard will be possible through the application of a dual bed NO X adsorber system ( i. e., a system that allows regeneration to be controlled external to the engine). This approach can work well for generator set applications where packaging constraints and vibration issues are greatly reduced. Since this approach requires limited engine redesign, it would be an appealing approach for these large engines sold in very low volumes. NO X adsorber 50 Emerachem EMxTM Datasheet  Describing the EMx IC ( Internal Combustion) System Air Docket OAR 2003 0012 0948.

51 See for example 68 FR 28375, May 23, 2003.

52 Fleetguard StableGuardTM Urea Premix for use with SCR NOX Reduction Systems, Air Docket A 2001 28 Item IV A 04.

72 systems for stationary power generation ( systems that never move) are available today on a retrofit basis, and we believe with further development to address packaging and durability concerns that similar systems can be applied to mobile generator sets. 50 A second possible technology option for engines in this category is urea SCR. The challenges for urea SCR in mobile applications are well known, specifically a lack of urea infrastructure to provide urea refill at diesel fueling locations and a need to ensure that urea is added as necessary in use. 51 These hurdles can be addressed more easily for generator sets than for virtually any other mobile source emission category. Although nonroad generator sets are mobile, in operation they remain at a fixed location where fuel is delivered to them periodically ( i. e., a 1,200 hp generator set does not and cannot pull into the local truck stop for a fuel fill). Therefore, the same infrastructure that currently provides urea delivery for stationary power generation can also be utilized for nonroad generator set applications. 52 It would still remain for the manufacturer to develop a mechanism to ensure urea refill, but we believe it is likely that solutions to this problem can be addressed through monitoring as for stationary source emissions or other technology options ( e. g., a urea interlock that precludes engine operation without the presence of urea).

Either of these technology approaches could be applied to realize an approximately 90 percent reduction from the current Tier 2 emission levels for these engines in order to comply with an emission standard of 0.50 g/ bhp hr. The 0.50 g/ bhp hr standard is different from our proposed level of 0.30 g/ bhp hr reflecting the changes we have made in this final action to the implementation schedule for this class of engines and therefore our projections for a technology path. At the time of the proposal, we projected that this class of engine would follow an integrated two step technology path. We are now finalizing a program that anticipates the application of 90 percent effective NO X control to diesel engines for use in generator sets without a reduction in engine out NO X levels beyond Tier 2. This reflects our desire to focus on getting the largest emission reduction possible in the near term ( beginning in 2011) from these engines. Where we believe additional technology development is needed, as is the case for mobile machines over 750 hp, we are finalizing a more gradual emission reduction technology pathway anticipating further reductions in engine out NO X emissions followed by a possible future action to reduce emissions further as described in section II. A. RIA chapter <IP_ADDRESS>.3 describes NO X adsorber effectiveness to control NO X emissions including effectiveness over the NTE region. The discussion there is equally applicable to engines above and below 750 hp regarding NTE 73 performance because the key attribute of NTE performance ( exhaust temperature) is similar for engines across the horsepower range.

For engines over 750 hp used in mobile machines ( and for 750   1200 hp generator sets from 2011 until 2015) we are setting a new NO X standard of 2.6 g/ bhp hr beginning in 2011. We are predicating this level of emission control ( an approximate 50 percent reduction from Tier 2) on an improved combustion system and proven engine based NO X control technologies. Specifically, we believe manufacturers can apply either proven cooled EGR technology, or apply additional levels of engine boost, a limited form of Miller Cycle operation, and increased intercooling capacity for the two stage turbocharging systems that are used on these engines. The second approach for in cylinder emissions reductions is similar in description at least to the Caterpillar ACERT technology which we believe could be another path for compliance with this standard. We are projecting a modest increase in heat rejection to the engine coolant for these incylinder emission control solutions and have accounted for those costs in our cost analysis. These approaches for NO X reduction have been proven for on highway diesel engines since 2003 including compliance with NTE provisions similar to those for nonroad engines finalized here. We can conclude based on the on highway experience that the NTE provisions can be met for engines in this horsepower category. One commenter suggested that a standard of 3.5 g/ bhp hr would be achievable in this time frame. As described here, we believe that further emission reductions to 2.6 g/ bhp hr are possible in this time frame. Engine manufacturers have indicated to the Agency that they believe this level of in cylinder emission control can be realized for these very large diesel engines by 2011. We are deferring any decision on setting aftertreatment based NO X standards for mobile machinery above 750 hp to allow additional time to evaluate the technical issues involved, as discussed in section II. A. 4.

NMHC Standards We are setting two different NMHC emission standards for engines in this category linked to the technologies used to control PM emissions. We are requiring all engines over 750 hp to meet an NMHC standard of 0.30 g/ bhp hr starting in 2011. As explained earlier, in 2011 all engines over 750 hp must meet a PM emission standard of 0.075 g/ bhp hr. We are projecting that manufacturers will meet this standard through improvements in in cylinder emission control of PM ( in conjunction with use of 15 ppm sulfur diesel fuel). These PM control technologies, increased fuel injection pressure, improved electronic controls and enhanced combustion system designs will concurrently lower NMHC emissions to the NMHC standard of 0.30 g/ bhp hr.

The second step in our NMHC standards is to a level of 0.14 g/ bhp hr, consistent with the standard for on highway diesels beginning in 2007 and for other nonroad diesel engines from 75 to 750 hp beginning in 2011. This change in NMHC standards is timed to coincide with the requirement that engines over 750 hp meet stringent PM emission standards that we believe will require the use of catalyst based diesel particulate filter systems. These systems are expected to incorporate oxidation catalyst functions to control the SOF portion of diesel PM and to promote robust soot regeneration within the filter. This same oxidation function is highly effective at 53 The 2013 NOX+ NMHC standard is a new standard only for engines in the 25 50 hp category.

For engines in the 50 75 hp category, 3.5 g/ bhp hr NOX+ NMHC is the existing Tier 3 emission standard which will now also apply across the new regulated test cycles ( e. g., NRTC).

74 controlling NMHC emissions ( the RIA documents reductions of more than 80 percent) and will result in a reduction in NMHC emissions below the 0.14 g/ bhp hr standard for these engines. As the high level of NMHC control afforded by the application of this technology is broadly realized across the wide range of diesel engine operation, it will allow for compliance with the NTE provisions as well. Although in practice we expect that NMHC emissions may be lower than the 0.14 g/ bhp hr standard, we have not finalized a more stringent standard for NMHC in order to maintain consistency with the NMHC standard we are finalizing for engines from 75 hp to 750 hp, for which the NMHC standard is in part based on feasibility considerations for NO X adsorber catalyst systems that use diesel fuel to regenerate themselves ( with consequent increased NMHC emissions during regeneration events). We believe this is appropriate considering our expectation that NO X adsorber technology will be found feasible for all nonroad engines over 750 hp.

4. Are the New Tier 4 Standards for Engines 25   75 hp Feasible?

As discussed in section II. B, our standards for 25   75 hp engines consist of a 2008 transitional standard and long term 2013 standards. The transitional standard is a 0.22 g/ bhp hr PM standard. The 2013 standards consist of a 0.02 g/ bhp hr PM standard and a 3.5 g/ bhp hr NMHC+ NO X standard. 53 As discussed in section II. A, the transitional standard is optional for 50 75 hp engines, as the 2008 implementation date is the same as the effective date of the Tier 3 standards. Manufacturers may decide, at their option, not to undertake the 2008 transitional PM standard, in which case their implementation date for the 0.02 g/ bhp hr PM standard begins in 2012. The remainder of this section discusses what makes the 25 75 hp category unique and why the standards are technologically feasible.

a. What makes the 25   75 hp category unique?

As EPA explained in the proposal, and as discussed in section II. A, one cannot assume that highway technologies are automatically transferable to 25   75 hp nonroad engines. In contrast with 75   750 hp engines, which share similarities in displacement, aspiration, fuel systems, and electronic controls with highway diesel engines, engines in the 25   75 hp category have a number of technology differences from the larger engines. These include a higher percentage of indirect injection fuel systems, and a low fraction of turbocharged engines ( see generally RIA chapter 4.1). The distinction in the under 25 hp category is even more pronounced, with no turbocharged engines, nearly one fifth of the engines have two cylinders or less, and a significant majority of the engines have indirect injection fuel systems.

The distinction is particularly marked with respect to electronically controlled fuel systems. These are commonly available in the power categories greater than or equal to 75 hp, 54 As discussed in section II. B., manufacturers can choose, at their option, to pull ahead the 2013 PM standard for the 50 75 hp engines to 2012, in which case they do not need to comply with the transitional 2008 PM standard.

55 However, a manufacturer can choose to comply over the TRU cycle including the associated NTE provisions. Compliance with the NTE for engines selecting to certify on the TRU cycle is straightforward because by the very nature of the products, their operation is directly limited to a small range of operating modes over which compliance with the emission standard has already been shown.

75 but, based on the available certification data as well as our discussions with engine manufacturers, we believe there are very limited numbers, if any, in the 25   75 hp category ( and no electronic fuel systems in the less than 25 hp category). The research and development work being performed today for the heavy duty highway market is targeted at engines which are 4 cylinders or more, direct injection, electronically controlled, turbocharged, and with per cylinder displacements greater than 0.5 liters. As discussed in more detail below, as well as in section II. B. 5 ( regarding the under 25 hp category), these engine distinctions are important from a technology perspective and warrant a different set of standards for the 25   75 hp category ( as well as for the under 25 hp category).

b. Are the new Tier 4 standards for 25   75 hp engines technologically feasible?

This section will discuss the technical feasibility of both the interim 2008 PM standard and the 2013 standards. For an explanation and discussion of the implementation dates, please refer to section II. A.

i. 2008 PM Standards54 We are today finalizing the interim PM control program as proposed for engines in the power category from 25   75 hp. The new PM standard for 2008 is 0.22 g/ bhp hr over the appropriate steady state test cycle ( the NRTC and NTE do not apply, for the reasons explained below). 55 The standard is premised on the use of 500 ppm sulfur diesel fuel and the potential for improvements in engine out emission control where possible or the application of a diesel oxidation catalyst ( DOC). Some commenters raised concerns that this level of emission control from diesel engines may not be possible in 2008 without fuel cleaner than 500 ppm or without changes in the Tier 3 NMHC+ NO X emission standards. Other commenters, including some engine manufacturers, supported this interim program. As explained in the following sections, we continue to believe that these standards are appropriate and feasible in the leadtime provided.

Engines in the 25   50 hp category must meet Tier 2 NMHC+ NO X and PM standards today. We have examined the model year 2004 engine certification data for engines in the 25   50 hp category. These data indicate that over 35 percent of the engine families meet the 2008 0.22 g/ bhp hr PM standard and 5.6 g/ bhp hr NMHC+ NO X standard ( unchanged from Tier 2 in 2008) 56 The Tier 1 and Tier 2 standards for this power category must be demonstrated on one of a variety of different engine test cycles. The appropriate test cycle is selected by the engine manufacturer based on the intended in use application of the engine.

57 EPA Memorandum " Documentation of the Availability of Diesel Oxidation Catalysts on Current Production Nonroad Diesel Equipment," William Charmley. Copy available in EPA Air Docket A 2001 28 Item II B 15.

76 today ( even without 500 ppm sulfur diesel fuel). At the time of the proposal, we had analyzed model year 2002 data for this power range, which at that time indicated approximately 10 percent of the engine families complied with the 2008 requirements. The most recent data for model year 2004 indicates substantial progress has already been made in just the past few year in lowering emissions from these engines. This is primarily due to the implementation of the Tier 2 standards in model year 2004. The model year 2001 certification data also showed the 2008 standard were achievable using a mix of engine technologies ( IDI and DI, turbocharged and naturally aspirated) tested on a variety of certification test cycles. 56 A detailed discussion of these data is contained in the RIA.

At the time of the proposal, no certification data was available for engines in the 50 75 hp range, because those engines were not subject to a Tier 1 standard and were not subject to Tier 2 standards until model year 2004. We have now had an opportunity to analyze the model year 2004 certification data for engines in the 50 75 hp range. These data shows that more than 70 percent of the engine families in this power range are capable of meeting the 2008 PM standards today. However, most of these engines do not yet meet the 3.5 g/ bhp hr Tier 3 NMHC+ NO X standard, which is required in 2008. We expect that to comply with the Tier 3 standards, these engines will use technologies such as EGR and electronically controlled fuel injection systems ( and we included the costs of these technologies in assessing the costs of the Tier 3 standards). These technologies have been shown to reduce NO X emissions by 50 percent without increasing PM emissions. The certification data show that for the 70 percent of the engine families which meet the 2008 Tier 4 PM standard ( 0.22 g/ bhp hr), a NO X reduction of less than 50 percent is needed for most of these engines to meet the 2008 Tier 4 NMHC+ NO X standard. A detailed discussion of these data is contained in the RIA.

In addition to using known engine out techniques, we also project that the 2008 standards can be achieved with the use of DOCs. DOCs are passive flow through emission control devices which are typically coated with a precious metal or a base metal washcoat. DOCs have been proven to be durable in use on both light duty and heavy duty diesel applications. In addition, DOCs have already been used to control carbon monoxide on some nonroad applications. 57 Some commenters raised concerns that DOCs could actual increase PM emissions when used on 500 ppm sulfur diesel fuel due to the potential for oxidation of the sulfur in the fuel to sulfate PM. While we agree with the commenters that sulfur reductions are important to control PM and in the long term that a 15 ppm fuel sulfur level will be the best solution, we disagree with the 77 assertion that the amount of sulfate PM formed from a DOC will be such that compliance with the 0.22 g/ bhp hr standard will be infeasible. While commenters shared data showing increased PM emissions when DOCs are used, we have similarly found data ( included in the RIA) that shows an overall reduction in emissions. To understand this discrepancy, it is important to realize that DOCs can be designed for operation on a range of fuel sulfur levels. The lower the fuel sulfur level, the more effective the PM oxidation function, but even at 500 ppm sulfur a properly designed DOC will realize a net reduction in PM emissions. DOCs have been successfully applied to diesel engines for on highway applications for PM control on 500 ppm fuel since 1994 through careful design of the DOC trading off PM reduction potential and sulfur oxidation potential. The RIA contains additional analysis describing DOC function, and its expected effectiveness when applied to nonroad diesel engines.

Other commenters argued that the application of DOC to diesel engines in this category would lead to an even greater emission reduction than estimated in our proposal, thus allowing the Agency to finalize a lower PM standard. While we agree that some engines will have lower emissions than required to meet the standard and that in the long term ( once 15 ppm fuel is widely available) the PM emissions will be further reduced, we do not believe that an emission level lower than 0.22 g/ bhp hr will be generally feasible in 2008 due to the sulfur level of diesel fuel of 500 ppm sulfur and the potential for sulfate PM formation.

In summary then, there are two likely means by which companies can comply with the interim 2008 PM standard. First, engine manufacturers can comply with this standard using known engine out techniques ( e. g., optimizing combustion chamber designs, fuel injection strategies). In fact, some fraction of engines already would comply with the emission standard. In addition, some engine manufacturers may choose to use diesel oxidation catalysts to meet this standard. Our cost analysis makes the conservative assumption ( i. e., the higher cost assumption) that all manufacturers will use DOC catalysts to comply with these emission standards.

Based on the existence of a number of engine families which already comply with the 0.22 g/ bhp hr PM standard ( and the 2008 NMHC+ NO X standard), and the availability of well known PM reduction technologies such as engine out improvements and diesel oxidation catalysts, we project that the 0.22 g/ bhp hr PM standards is technologically feasible by model year 2008.

ii. 2013 Standards For engines in the 25 50 range, we are finalizing standards commencing in 2013 of 3.5 g/ bhp hr for NMHC+ NO X and 0.02 g/ bhp hr for PM. For the 50   75 hp engines, we are finalizing a 0.02 g/ bhp hr PM standard which will be implemented in 2013, and for those manufacturers who choose to pull ahead the standard one year, 2012 ( manufacturers who choose to pull ahead the 2013 standard for engines in the 50   75 range do not need to comply with the transitional 2008 PM standard). A more complete discussion of the options available to manufacturers and the nature of the transitional program can be found in section II. A. These 58 " The Optimized Deutz Service Diesel Particulate Filter System II," H. Houben et. al., SAE Technical Paper 942264, 1994 and " Development of a Full Flow Burner DPF System for Heavy Duty Diesel Engines," P. Zelenka et. al., SAE Technical Paper 2002 01 2787, 2002.

78 standards are measured using the NRTC and steady state tests. These engines also will be subject to the NTE starting with the 2013 model year.

PM Standard For engines in the horsepower category from 25   75 hp, we are finalizing a PM standard of 0.02 g/ bhp hr based on the application of catalyzed diesel particulate filters to engines in this category. We received a wide range of comments on our proposal with some arguing that the emission standard could be met earlier than 2013 and others arguing that while technically possible to apply PM filters to engines in this category, that it was not economically or otherwise practical to do so.

The RIA discusses in detail catalyzed diesel particulate filters, including explanations of how CDPFs reduce PM emissions, and how to apply CDPFs to nonroad engines. We have concluded, as explained above, that CDPFs can be used to achieve the 0.01 g/ bhp hr PM standard for 75   750 hp engines. As also discussed in section II. B. 2. a above, PM filters will require active back up regeneration systems for many nonroad applications above and below 75 hp because low temperature operation is an issue across all power categories. One commenter raised concerns regarding the low exhaust temperatures possibly experienced by small nonroad engines and argued that such low temperatures make PM filter regeneration impossible absent the use of active regeneration technologies. We agree with the commenter that active regeneration, as described previously, may be necessary and have included the cost for such systems in our cost estimates. See section II. B. 1. a. A number of secondary technologies are likely required to enable proper regeneration, including possibly electronic fuel systems such as common rail systems which are capable of multiple post injections which can be used to raise exhaust gas temperatures to aid in filter regeneration.

Particulate filter technology, with the requisite trap regeneration technology, can also be applied to engines in the 25 to 75 hp range. As explained earlier, the fundamentals of how a filter is able to reduce PM emissions are not a function of engine power, so that CDPF's are just as effective at capturing soot emissions and oxidizing SOF on smaller engines as on larger engines. The PM filter regeneration systems described in section II. B. 2 are also applicable to engines in this size range and are likewise feasible. There are specific trap regeneration technologies which we believe engine manufacturers in the 25   75 hp category may prefer over others. For example, some manufacturers may choose to apply an electronically controlled secondary fuel injection system ( i. e., a system which injects fuel into the exhaust upstream of a PM filter). Such a system has been commercially used successfully by at least one nonroad engine manufacturer, and other systems have been tested by technology companies. 58 However, we recognize that the application 79 of these technologies will be challenging and will require additional time to develop. We therefore disagree with commenters who say that the standard could be met sooner and have decided to finalize the implementation schedule as proposed.

As we proposed, we are finalizing a slightly higher PM standard ( 0.02 g/ bhp hr rather than 0.01) for engines in this power category. As discussed in the preamble to the proposed rule and in some detail in the RIA, with the use of a CDPF, the PM emissions emitted by the filter are primarily derived from the fuel sulfur ( 68 FR 28389 28390, May 23, 2003). The smaller power category engines tend to have higher fuel consumption per unit of work than larger engines. This occurs for a number of reasons. First, the lower power categories include a high fraction of IDI engines which by their nature consume approximately 15 percent more fuel than a DI engine. Second, as engine displacements get smaller, the engine's combustion chamber surface to volume ratio increases. This leads to higher heat transfer losses and therefore lower efficiency and higher fuel consumption. In addition, frictional losses are a higher percentage of total power for the smaller displacement engines which also results in higher fuel consumption. Because of the higher fuel consumption rate, we expect a higher particulate sulfate level, and therefore we have set a 0.02 g/ bhp hr standard for engines in this power category. We did not receive any comments on our proposal arguing that the technical basis for this higher PM level was inappropriate.

The 0.02 g/ bhp hr standard applies to all of the test cycles applicable to engines in this power category ( i. e., the NRTC including cold start, the ISO C1, D2 and G2 cycles and the alternative TRU and RMC cycles, as appropriate). Our feasibility analysis summarized here and detailed in the RIA takes into consideration these different test cycles. The control technologies work in a similar manner and provide the same high level of emission control across these different operating regimes including the NTE. The most significant effect on emission performance is related to sulfate PM formation at high load, high temperature operating conditions. As the RIA details, this level of high sulfate formation rate is not high enough to preclude compliance with the PM emission standard with 15 ppm fuel sulfur on the regulated test cycles nor is it high enough to preclude compliance with the NTE provisions. At higher fuel sulfur levels however, compliance with the PM emission standard would not be feasible.

The majority of negative comments on our proposal to set a PM standard based on the control possible from PM filter technologies focused on the economic and technical challenges to apply these technologies and the major engine technology enabler, electronic fuel systems, to smaller diesel engines. Some commenters acknowledged that the technologies were " technically feasible" but not economically feasible or practical for engines in this power category. While we acknowledge that the application of these technologies to diesel engines in this horsepower category will be challenging and have given consideration to this in setting the timing for the new standard, we believe that the technical path for compliance is clear and that the cost estimates we have made for these engines accurately represent this technical path. As discussed in the RIA, at the time of the proposal we projected no significant penetration of electronic fuel systems for engines in the 50   100 hp range prior to the Tier 3 standards ( 2008). Since the proposal, new information regarding model year 2004 engine certifications has become available. That data 59 See section 2.2 through 2.3 in " Nonroad Diesel Emission Standards  Staff Technical Paper,"

EPA Publication EPA420 R 01 052, October 2001. Copy available in EPA Air Docket A 2001 28.

80 show 18 percent of the engines in the 75   100 hp category already use electronically controlled fuel systems. In model year 2001, no engines in this category used electronic fuel systems. We believe this strong trend toward the introduction of more advanced electronic fuel system technology will continue in the future and, importantly for engines in the 25   75 hp category, will extend to ever smaller engine categories due to the user benefits provided by the technology and the falling cost for such systems. However, acknowledging the substantial time between now and 2012, and the potential for technologies to mature faster or slower than we are estimating here, we have decided to conduct a technology review of these standards as described in section II. A above. This review will provide EPA with another opportunity to confirm that the technical path laid out here is indeed progressing in a manner consistent with our expectations.

NMHC+ NO X Standard As we proposed, we are finalizing a 3.5 g/ bhp hr NMHC+ NO X standard for engines in the 25   50 hp range for 2013. We received limited comments arguing that the NMHC+ NO X standard should be less stringent. Like the PM standard, some commenters argued that the NO X standard would be costly and complicated, although not necessarily infeasible to apply. Other commenters argued that the NO X standard for engines in this category like the new standard for larger engines, should be based upon the application of advanced NO X catalyst based technologies. As described previously in section II. A, we do not believe that the catalyst based NO X technologies have matured to a state were we can accurately define a feasible technical path for compliance for engines in this power category. We intend to revisit this question in our technology review and if we find that a viable technical path can be described we will consider the appropriateness of a more stringent catalyst based standard.

The new standard aligns the NMHC+ NO X standard for engines in this power range with the Tier 3 standard for engines in the 50   75 hp range which are implemented in 2008. EPA's recent Staff Technical paper which reviewed the technological feasibility of the Tier 3 standards contains a detailed discussion of a number of technologies which are capable of achieving a 3.5 g/ bhp hr standard. These include cooled EGR, uncooled EGR, as well as advanced in cylinder technologies relying on electronic fuel systems and turbocharging. 59 These technologies are capable of reducing NO X emissions by as much as 50 percent. Given the Tier 2 NMHC+ NO X standard of 5.6 g/ bhp hr, a 50 percent reduction would allow a Tier 2 engine to comply with the 3.5 g/ bhp hr NMHC+ NO X standard set in this action. Therefore, we are projecting that 3.5 g/ bhp hr NO X+ NMHC standard is feasible with the addition of cooled EGR ( the basis for our cost analysis) or other equally effective in cylinder NO X control technology as described in the RIA and our recent Staff Technical Paper. In addition, because this NMHC+ NO X standard is concurrent with the 0.02 g/ bhp hr PM standards which we project will be achievable with the use of particulate filters, engine designers will have significant additional flexibility in reducing NO X 60 See section 8 of " Control of Emissions of Air Pollution from 2004 and Later Model Year Heavy Duty Highway Engines and Vehicles: Response to Comments," EPA document EPA420 R 00 011,

July 2000, and chapter 3 of " Regulatory Impact Analysis: Control of Emissions of Air Pollution from Highway Heavy duty Engines," EPA document EPA420 R 00 010, July 2000. Copies of both documents available in EPA docket A 2001 28.

81 because the PM filter will lessen the traditional concerns with the engine out NO X vs. PM tradeoff

Our recent highway 2004 standard review rulemaking ( see 65 FR 59896, October 2000) demonstrated that a diesel engine with advanced electronic fuel injection technology as well as NO X control technology such as cooled EGR is capable of complying with an NTE standard set at 1.25 times the laboratory based FTP standard. We project that the same technology ( electronic fuel systems and cooled EGR) are also capable for engine in the 25 75 hp range of complying with the NTE standard of 4.4 g/ bhp hr NMHC+ NO X ( 1.25 x 3.5) in 2013. This is based on the broad NO X reduction capability of cooled EGR technology, which is capable of reducing NO X emissions across the engine operating map ( including the NTE region) by at least 30 percent even under high load conditions. 60 Based on the information available to EPA and presented here, and giving appropriate consideration to the lead time necessary to apply the technology as well, we have concluded the 0.02 g/ bhp hr PM standard for engines in the 25   75 hp category and the 3.5 g/ bhp hr NMHC+ NO X standards for the 25   50 hp engines are achievable.

5. Are the Standards for Engines under 25 hp Feasible?

As we explained at proposal and as discussed in section II. A, the new PM standard for engines less than 25 hp is 0.30 g/ bhp hr beginning in 2008. The certification test cycle for this standard is the ISO C1 cycle ( or other appropriate steady state test as defined by the engine's intended use) from 2008 through 2012. Beginning in 2013, the NRTC ( with cold start) and the NTE will also apply to engines in this category. As discussed below, we are not setting a new standard more stringent than the existing Tier 2 NMHC+ NO X standard for this power category at this time. This section describes what makes the less than 25 hp category different and why the standards are technologically feasible.

a. What makes the under 25 hp category unique?

As we explained at proposal and in the RIA, nonroad engines less than 25 hp are the least sophisticated nonroad diesel engines from a technological perspective. All of the engines currently sold in this power category lack electronic fuel systems and turbochargers. Nearly 20 percent of the products have two cylinders or less, and 14 percent of the engines sold in this category are single cylinder products, a number of these have no batteries and are crank start 61 The Tier 1 and Tier 2 standards for this power category must be demonstrated on one of a variety of different engine test cycles. The appropriate test cycle is selected by the engine manufacturer based on the intended in use applications( s) of the engine.

82 machines, much like today's simple walk behind lawnmower engines. In addition, given what we know today and taking into account the Tier 2 standards which have not yet been implemented, we are not projecting any significant penetration of advanced engine technology, such as electronically controlled fuel systems, into this category in the next 5 to 10 years.

b. What data indicate that the standards are feasible?

We project the Tier 4 PM standard can be met by 2008 based on: the existence of a large number of engine families which meet the new standards today; the use of engine out reduction techniques; and the use of diesel oxidation catalysts.