[Federal Register Volume 84, Number 173 (Friday, September 6, 2019)]
[Rules and Regulations]
[Pages 46883-46885]
[FR Doc No: 2019-19252]

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DEPARTMENT OF HOMELAND SECURITY

Coast Guard

33 CFR Part 165

[Docket No. USCG-2019-0678]
RIN 1625-AA00

Safety Zone; Incline Village Wedding Fireworks Display, Crystal
Bay, Incline Village, NV

AGENCY: Coast Guard, DHS.

ACTION: Temporary final rule.

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SUMMARY: The Coast Guard is establishing a temporary safety zone on the
navigable waters of Crystal Bay near the Hyatt Lake Tahoe Nevada boat
dock in support of the Incline Village Wedding Fireworks Display on
September 8, 2019. This safety zone is necessary to protect personnel,
vessels, and the marine environment from the dangers associated with
pyrotechnics. Unauthorized persons or vessels are prohibited from
entering into, transiting through, or remaining in the safety zone
without permission of the Captain of the Port San Francisco or a
designated representative.

DATES: This rule is effective from 4 p.m. to 9:40 p.m. on September 8,
2019.

ADDRESSES: To view documents mentioned in this preamble as being
available in the docket, go to https://www.regulations.gov, type USCG-
2019-0678 in the ``SEARCH'' box and click ``SEARCH.'' Click on Open
Docket Folder on the line associated with this rule.

FOR FURTHER INFORMATION CONTACT: If you have questions on this rule,
call or email Lieutenant Junior Grade Jennae Cotton, Waterways
Management, U.S. Coast Guard; telephone<PHONE_NUMBER>, email
<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

I. Table of Abbreviations

CFR Code of Federal Regulations
COTP Captain of the Port San Francisco
DHS Department of Homeland Security
Sec.  Section
U.S.C. United States Code

II. Background Information and Regulatory History

    The Coast Guard is issuing this temporary rule without prior notice
and opportunity to comment pursuant to authority under section 4(a) of
the Administrative Procedure Act (APA) (5 U.S.C. 553(b)). This
provision authorizes an agency to issue a rule without prior notice and
opportunity to comment when the agency for good cause finds that those
procedures are ``impracticable, unnecessary, or contrary to the public
interest.'' Under 5 U.S.C. 553(b)(B), the Coast Guard finds that good
cause exists for not publishing a notice of proposed rulemaking with
respect to this rule because it is impracticable. The Coast Guard did
not receive final details for this event until July 30, 2019. It is
impracticable to go through the entire notice of proposed rulemaking
process because the Coast Guard must establish this temporary safety
zone by September 8, 2019 and lacks sufficient time to provide a
reasonable comment period and consider those comments before issuing
the rule.
    Under 5 U.S.C. 553(d)(3), the Coast Guard finds that good cause
exists for making this rule effective less than 30 days after
publication in the Federal Register. For similar reasons as stated
above, notice and comment procedures would be impractical in this
instance due to the short notice provided for this event.

III. Legal Authority and Need for Rule

    The Coast Guard is issuing this rule under authority 46 U.S.C.
70034 (previously 33 U.S.C. 1231). The Captain of the Port San
Francisco has determined that potential hazards associated with the
Incline Village Wedding Fireworks Display on September 8, 2019, will be
a safety concern for anyone within a 100-foot radius of the fireworks
barge during loading, staging, and transit, and anyone within a 210-
foot radius of the fireworks barge starting 30 minutes before the
fireworks display is scheduled to commence and ending 30 minutes after
the conclusion of the fireworks display. For this reason, this
temporary safety zone is needed to protect personnel, vessels, and the
marine environment in the navigable waters around the fireworks barge
during the fireworks display.

IV. Discussion of the Rule

    This rule establishes a safety zone from 4 p.m. until 9:40 p.m. on
September 8, 2019 during the loading, staging, and transit of the
fireworks barge in Crystal Bay in Incline Village, until 30 minutes
after completion of the fireworks display. From 4 p.m. to 8:30 p.m. on
September 8, 2019, during the loading, staging, and transit of the

fireworks barge until 30 minutes prior to the start of the fireworks
display, the safety zone will encompass the navigable waters around and
under the fireworks barge, from surface to bottom, within a circle
formed by connecting all points 100 feet out from the fireworks barge.
Loading the pyrotechnics onto the fireworks barge is scheduled from 4
p.m. to 5 p.m. on September 8, 2019, at the Incline Village boat ramp
in Incline Village, NV.
    The fireworks barge will remain at the Incline Village boat ramp
until the start of its transit to the display location. Towing of the
barge from the Incline Village boat ramp to the display location is
scheduled to take place from 6 p.m. to 6:10 p.m. on September 8, 2019,
where it will remain until the conclusion of the fireworks display.
    At 8:30 p.m. on September 8, 2019, 30 minutes prior to the
commencement of the 10-minute Incline Village Wedding Fireworks
Display, the safety zone will increase in size and encompass the
navigable waters around and under the fireworks barge, from surface to
bottom, within a circle formed by connecting all points 210 feet from
the circle center at approximate position 39[deg]14'00'' N,
119[deg]56'56'' W (NAD 83). The safety zone will terminate at 9:40 p.m.
on September 8, 2019.
    This temporary safety zone restricts navigation in the vicinity of
the fireworks loading, staging, transit, and firing site. Except for
persons or vessels authorized by the COTP or the COTP's designated
representative, no person or vessel may enter or remain in the
restricted areas. A ``designated representative'' means a Coast Guard
Patrol Commander, including a Coast Guard coxswain, petty officer, or
other officer operating a Coast Guard vessel or a Federal, State, or
local officer designated by or assisting the COTP in the enforcement of
the safety zone or assisting the COTP in the enforcement of the safety
zone.
    These regulations are needed to keep spectators and vessels away
from the immediate vicinity of the fireworks firing sites to ensure the
safety of participants, spectators, and transiting vessels.

V. Regulatory Analyses

    We developed this rule after considering numerous statutes and
Executive orders related to rulemaking. Below we summarize our analyses
based on a number of these statutes and Executive orders, and we
discuss First Amendment rights of protestors.

A. Regulatory Planning and Review

    Executive Orders 12866 and 13563 direct agencies to assess the
costs and benefits of available regulatory alternatives and, if
regulation is necessary, to select regulatory approaches that maximize
net benefits. Executive Order 13771 directs agencies to control
regulatory costs through a budgeting process. This rule has not been
designated a ``significant regulatory action,'' under Executive Order
12866. Accordingly, this rule has not been reviewed by the Office of
Management and Budget (OMB), and pursuant to OMB guidance it is exempt
from the requirements of Executive Order 13771.
    This regulatory action determination is based on the size, limited
duration, and narrowly tailored geographic area of the safety zone.
This safety zone impacts a 210-foot radius area of Lake Tahoe in
Incline Village for a limited duration of 5 hours and 40 minutes. The
vessels desiring to transit through or around the temporary safety zone
may do so upon express permission from the COTP or the COTP's
designated representative.

B. Impact on Small Entities

    The Regulatory Flexibility Act of 1980, 5 U.S.C. 601-612, as
amended, requires Federal agencies to consider the potential impact of
regulations on small entities during rulemaking. The term ``small
entities'' comprises small businesses, not-for-profit organizations
that are independently owned and operated and are not dominant in their
fields, and governmental jurisdictions with populations of less than
50,000. The Coast Guard certifies under 5 U.S.C. 605(b) that this rule
will not have a significant economic impact on a substantial number of
small entities.
    While some owners or operators of vessels intending to transit the
temporary safety zone may be small entities, for the reasons stated in
section V.A. above, this rule will not have a significant economic
impact on any vessel owner or operator.
    Under section 213(a) of the Small Business Regulatory Enforcement
Fairness Act of 1996 (Pub. L. 104-121), we want to assist small
entities in understanding this rule. If the rule would affect your
small business, organization, or governmental jurisdiction and you have
questions concerning its provisions or options for compliance, please
contact the person listed in the FOR FURTHER INFORMATION CONTACT
section.
    Small businesses may send comments on the actions of Federal
employees who enforce, or otherwise determine compliance with, Federal
regulations to the Small Business and Agriculture Regulatory
Enforcement Ombudsman and the Regional Small Business Regulatory
Fairness Boards. The Ombudsman evaluates these actions annually and
rates each agency's responsiveness to small business. If you wish to
comment on actions by employees of the Coast Guard, call 1-888-REG-FAIR
(1-888-734-3247). The Coast Guard will not retaliate against small
entities that question or complain about this rule or any policy or
action of the Coast Guard.

C. Collection of Information

    This rule will not call for a new collection of information under
the Paperwork Reduction Act of 1995 (44 U.S.C. 3501-3520).

D. Federalism and Indian Tribal Governments

    A rule has implications for federalism under Executive Order 13132,
Federalism, if it has a substantial direct effect on the States, on the
relationship between the national government and the States, or on the
distribution of power and responsibilities among the various levels of
government. We have analyzed this rule under that Order and have
determined that it is consistent with the fundamental federalism
principles and preemption requirements described in Executive Order
13132.
    Also, this rule does not have tribal implications under Executive
Order 13175, Consultation and Coordination with Indian Tribal
Governments, because it does not have a substantial direct effect on
one or more Indian tribes, on the relationship between the Federal
Government and Indian tribes, or on the distribution of power and
responsibilities between the Federal Government and Indian tribes. If
you believe this rule has implications for federalism or Indian tribes,
please contact the person listed in the FOR FURTHER INFORMATION CONTACT
section above.

E. Unfunded Mandates Reform Act

    The Unfunded Mandates Reform Act of 1995 (2 U.S.C. 1531-1538)
requires Federal agencies to assess the effects of their discretionary
regulatory actions. In particular, the Act addresses actions that may
result in the expenditure by a State, local, or tribal government, in
the aggregate, or by the private sector of $100,000,000 (adjusted for
inflation) or more in any one year. Though this rule will not result in
such an expenditure, we do discuss the effects of this rule elsewhere
in this preamble.

F. Environment

    We have analyzed this rule under Department of Homeland Security
Directive 023-01 and U.S. Coast Guard Environmental Planning Policy,
COMDTINST 5090.1 (series), which guide the Coast Guard in complying
with the National Environmental Policy Act of 1969 (42 U.S.C. 4321-
4370f), and have determined that this action is one of a category of
actions that do not individually or cumulatively have a significant
effect on the human environment. This rule involves a safety zone
lasting 5 hours and 40 minutes that prevents entry to a 210-foot radius
area of Lake Tahoe in Incline Village. It is categorically excluded
from further review under paragraph L60(a) in Table 3-1 of Department
of Homeland Security Directive 023-01. A Record of Environmental
Consideration supporting this determination is available in the docket
where indicated under ADDRESSES.

G. Protest Activities

    The Coast Guard respects the First Amendment rights of protesters.
Protesters are asked to contact the person listed in the FOR FURTHER
INFORMATION CONTACT section to coordinate protest activities so that
your message can be received without jeopardizing the safety or
security of people, places or vessels.

List of Subjects in 33 CFR Part 165

    Harbors, Marine safety, Navigation (water), Reporting and
recordkeeping requirements, Security measures, Waterways.

    For the reasons discussed in the preamble, the Coast Guard amends
33 CFR part 165 as follows:

PART 165--REGULATED NAVIGATION AREAS AND LIMITED ACCESS AREAS

0
1. The authority citation for part 165 continues to read as follows:

    Authority:  46 U.S.C 70034, 70051; 33 CFR 1.05-1, 6.04-1, 6.04-
6, and 160.5; Department of Homeland Security Delegation No. 0170.1.

0
2. Add Sec.  165.T11-993 to read as follows:

Sec.  165.T11-993  Safety Zone; Incline Village Wedding Fireworks
Display, Crystal Bay, Incline Village, NV.

    (a) Location. The following area is a safety zone: All navigable
waters of Crystal Bay, from surface to bottom, within a circle formed
by connecting all points 100 feet out from the fireworks barge during
the loading and staging at the Incline Village boat ramp in Incline
Village, as well as during transit and arrival to the display location
in Incline Village, NV. Between 8:30 p.m. on September 8, 2019 and 9:40
p.m. on September 8, 2019, the safety zone will expand to all navigable
waters, from surface to bottom, within a circle formed by connecting
all points 210 feet out from the fireworks barge in approximate
position 39[deg]14'00'' N, 119[deg] 56'56'' W (NAD 83).
    (b) Definitions. As used in this section, ``designated
representative'' means a Coast Guard Patrol Commander, including a
Coast Guard coxswain, petty officer, or other officer operating a Coast
Guard vessel or a Federal, State, or local officer designated by or
assisting the Captain of the Port San Francisco (COTP) in the
enforcement of the safety zone.
    (c) Regulations. (1) Under the general safety zone regulations in
subpart B of this part, you may not enter the safety zone described in
paragraph (a) of this section unless authorized by the COTP or the
COTP's designated representative.
    (2) The safety zone is closed to all vessel traffic, except as may
be permitted by the COTP or the COTP's designated representative.
    (3) Vessel operators desiring to enter or operate within the safety
zone must contact the COTP or the COTP's designated representative to
obtain permission to do so. Vessel operators given permission to enter
or operate in the safety zone must comply with all lawful orders or
directions given to them by the COTP or the COTP's designated
representative. Persons and vessels may request permission to enter the
safety zone on VHF-23A or through the 24-hour Command Center at
telephone<PHONE_NUMBER>.
    (d) Enforcement period. This section will be enforced from 4 p.m.
on September 8, 2019 through 9:40 p.m. on September 8, 2019.
    (e) Information broadcasts. The COTP or the COTP's designated
representative will notify the maritime community of periods during
which this zone will be enforced in accordance with Sec.  165.7.

    Dated: August 28, 2019.
Marie B. Byrd,
Captain, U.S. Coast Guard, Captain of the Port, San Francisco.
[FR Doc. 2019-19252 Filed 9-5-19; 8:45 am]
 BILLING CODE 9110-04-P


A New Environmental Chamber for Evaluation of Gas Phase Chemical Mechanisms and Secondary Aerosol Formation By William P. L. Carter*,*, David R. Cocker III*,*, Dennis R. Fitz*, Irina L. Malkina*, Kurt Bumiller*, Claudia G. Sauer*, ¶ , John T. Pisano*, Charles Bufalino*, and Chen Song*,*

* College of Engineering Center for Environmental Research and Technology, University of California, Riverside, California 92521 * Department of Chemical and Environmental Engineering, University of California, Riverside, California 92521 ¶ Present Address: USP Indicators, Suppanstrasse 69, A 9020 Klagenfurt, Austria * Corresponding author Revised for Resubmission to Atmospheric Environment June 18, 2005 2 Abstract A new state of the art indoor environmental chamber facility for the study of atmospheric processes leading to the formation of ozone and secondary organic aerosol ( SOA)

has been constructed and characterized. The chamber is designed for atmospheric chemical mechanism evaluation at low reactant concentrations under well controlled environmental conditions. It consists of two collapsible 90 m3 FEP Teflon film reactors on pressure controlled moveable frameworks inside a temperature controlled enclosure flushed with purified air. Solar radiation is simulated with either a 200 kW Argon arc lamp or multiple blacklamps. Results of initial characterization experiments, all carried out under dry conditions, concerning NOx and formaldehyde offgasing, radical sources, particle loss rates, and background PM formation are described. Results of initial single organic  NOx and simplified ambient surrogate  NOx experiments to demonstrate the utility of the facility for mechanism evaluation under low NOx conditions are summarized and compared with the predictions of the SAPRC 99 chemical mechanism. Overall, the results of the initial characterization and evaluation indicate that this new environmental chamber can provide high quality mechanism evaluation data for experiments with NOx levels as low as ~ 2 ppb, though the results indicate some problems with the gas phase mechanism that need further study. Initial evaluation experiments for SOA formation, also carried out under dry conditions, indicate that the chamber can provide high quality secondary aerosol formation data at relatively low hydrocarbon concentrations. 3 Introduction Environmental chambers have been used for the past few decades to investigate processes leading to secondary pollutant formation such as ozone ( Jeffries et al, 1982; 1985a c; 1990; Gery et al, 1988; Hess et al, 1992; Simonaitis and Bailey, 1995; Simonaitis et al, 1997; Carter et al,

1995a; Carter, 2000; Dodge, 2000 and references therein) and secondary organic aerosol ( SOA).

( e. g., Odum et al., 1996, 1997; ; Griffin et al., 1999; Kleindienst et al., 1999; Barnes and Sidebottom, 2000; Cocker et al. 2001a c; Jang and Kamens, 2001; Seinfeld and Pankow, 2003 and references therein, Johnson et al, 2004, Montserrat et al, 2005). These chambers are essential for developing and evaluating chemical mechanisms or models for predicting the formation of secondary pollutants in the absence of uncertainties associated with emissions, meteorology, and mixing effects. Existing chambers have been used to develop the models now used to predict ozone formation ( Gery et al, 1988; Stockwell et al, 1990; Carter, 2000; Dodge, 2000 and references therein), and are beginning to provide data concerning formation of SOA ( e. g., Pandis et al., 1992; Griffin et al., 2001; Pun et al., 2003; Griffin et al., 2003, Johnson et al, 2004,

Montserrat et al, 2005). However, environmental chambers are not without uncertainties in characterization and variability and background effects ( Carter et al, 1982; Carter and Lurmann,

1991; Jeffries et al, 1992; Carter et al, 1995a; Dodge, 2000). This limits the utility of the data and the range of conditions under which the models or mechanisms can be reliably evaluated.

For example, because of background effects and analytical limitations, most chamber experiments to date have been conducted using levels of NOx and other pollutants that are significantly higher than those that currently occur in most urban and rural areas ( Dodge, 2000).

Even lower ambient NOx conditions are expected as we approach eventual attainment of the air quality standards. The nature of the radical and NOx cycles and the distribution of VOC oxidation products change as absolute levels of NOx are reduced. Because of this, one cannot necessarily be assured that the current mechanisms developed to simulate results of relatively high concentration experiments will satisfactorily simulate downwind or cleaner environments.

Background effects can be minimized by using large volume reactors and assuring that the matrix air is adequately purified, that appropriate wall material is utilized, and that steps are 4 taken to minimize introduction of ambient pollutants due to leaks or permeation. Large volume is also required for minimizing wall losses of aerosols or semi volatile aerosol precursors, which is important in studies of SOA formation. For this reason, until recently, most studies of SOA formation have been carried out in large outdoor chambers ( e. g., Jaoui et al., 2004; Griffin et al.,

1999, Montserrat et al, 2005). However, outdoor chambers have diurnal, daily and seasonal changes in temperature and actinic flux, which can increase uncertainties in characterization of run conditions for model evaluation and make systematic studies of temperature and humidity effects difficult. Recently a new indoor chamber was developed to address these concerns ( Cocker et al, 2001a), but that chamber was not designed to conduct experiments characterized for low pollutant conditions, and the blacklight light source employed does not represent that of natural sunlight in the longer wavelength region that affects some of the photooxidation processes ( Carter et al, 1995b).

This paper describes a new state of the art environmental chamber facility developed to minimize reactor effects in studies of VOC reactivity and provide a platform for low NOx and VOC ozone reactivity and secondary aerosol formation experiments. It also provides the technical background of the facility and assesses its ability and limitations for low NOx experiments. We discuss current reactor limitations and their implications for studies on ozone reactivity and SOA formation within Teflon reactors.

Facility Description The indoor facility comprises a 6m x 6m x 12m thermally insulated enclosure that is continually flushed with purified air at a rate of 1000 L min 1 and is located on the second floor of a laboratory building specifically designed to house it. Located directly under the enclosure on the first floor is an array of gas phase continuous and semi continuous gas phase monitors.

Within the enclosure are two ~ 90 m3 ( 5.5 m x 3 m x 5.5 m) maximum volume 2 mil FEP Teflon ® film reactors, a 200 kW Argon arc lamp, a bank of 115 W 4 ft blacklights, along with the light monitoring and aerosol instrumentation. A schematic of the enclosure is provided in Figure 1. 5 Enclosure The interior of the thermally insulated 450 m3 enclosure is lined with hard clear anodized aluminum sheeting to maximize the interior light intensity and homogenize the interior light intensity. A positive pressure is maintained between the enclosure and the surrounding room to reduce contamination of the reactor enclosure by the surrounding building air. The enclosure air is well mixed by the large air handlers that draw in air from inlets around the light and force the air through a false ceiling with perforated reflective aluminum sheets. The enclosure is temperature controlled with a ~ 30 ton (~ 105 KW cooling power) air conditioner capable of producing a temperature range of 5 to 45 C, controlled to better than ± 1 C.

Teflon Reactors The 2 mil ( 54 µ m) FEP Teflon ® reactors are mounted within the enclosure with a rigid bottom frame and a moveable top frame. The floor of the reactor is lined with Teflon ® film with openings for reactant mixing within and between reactors and 8 ports ranging in size from 0.64 to 1.3 cm for sample injection and withdrawal. The moveable top frame is raised and lowered with a motorized pulley system, which enables the user to expand ( during filling) and contract ( during an experiment or for flushing) the reactors as necessary. The rate of contraction or expansion is set to maintain a differential pressure of 5 pascal between the inside of the reactor and the enclosure. During experiments, the top frames are slowly lowered to maintain positive pressure as the volume decreases due to sampling, leaks, and permeation. The experiment is terminated when the final reactor volume reaches 1/ 3 of its maximum value ( typically about 10 hours, though less if there are leaks in a reactor). The elevator system coupled with differential pressure measurements allows for repeatable initial chamber volumes and allows for reactants to be injected with greater than 5% precision. The Teflon reactors are built in house using a PI G36 Pac Impulse Sealer ( San Rafael, CA) heat sealing device for all major seams and are mounted to the reactor floor and ceiling.

The Teflon reactors tend to eventually crack and leak after repeated use, with the failures usually occurring at the seams. Because of the positive pressure control this results in shorter times for experiments rather than dilution or contamination of the reactor. Leaks are repaired 6 using a polyester film tape with a silicone adhesive ( 3M Polyester Tape 8403) when needed, and the reactors are repaired periodically before leaks and repairs become excessive.

Pure Air System An Aadco 737 series ( Cleves, Ohio) air purification system produces compressed air at rates up to 1500 L min 1. The air is further purified by passing through canisters of Purafil ® and heated Carulite 300 ® followed by a filter pack to remove all particulate. The purified air within the reactor has no detectable non methane hydrocarbons (< 1 ppb), NOx (< 10 ppt), no detectable particles (< 0.2 particles cm 3), and a dew point below  40 C.

All the experiments discussed in this paper were carried out with unhumidified air, i. e.,

with a dew point below  40 C. A humidification system has now been constructed, and this system and results of humidified experiments will be discussed in a subsequent paper.

The reactors are cleaned between runs by reducing the reactor volume to less than 5% of its original volume and re filling it to its maximum volume with purified air at least six times. No residual hydrocarbons, NOx, or particles are detected after the cleaning process.

Light sources A 200 kW Argon arc lamp with a spectral filter ( Vortek co, British Columbia, Canada) is used as the primary means to irradiate the enclosure and closely simulate the entire UV Visible ground level solar spectra. The arc lamp is mounted on the far wall from the reactors at a minimum distance of 6m to provide uniform lighting within both reactors. Backup lighting is provided by banks of total 80 1.22 m, 115 W Sylvania 350BL blacklamps ( peak intensity at 350 nm) mounted on the same wall of the enclosure. These provide a low cost and efficient UV irradiation source within the reactor for experiments where the closer spectral match provided by the Argon arc system is not required. The light spectra and intensity characterization for these sources are discussed below. 7 Interreactor and Intrareactor mixing The two reactors are connected to each other through a series of custom solenoid valves and blowers. The system provides for rapid air exchange prior to the start of an experiment ensuring, that both reactors have identical concentrations of starting material. Each reactor can be premixed prior to the start of an experiment by Teflon coated fans located within the reactor.

Instrumentation The suite of traditional and non traditional instruments used to monitor gaseous species within the reactors complete with species detected and detection limits is listed and briefly described Table 1. All gas phase instruments are located directly below the enclosure on the first floor of the building.

The aerosol phase instrumentation present is also included in Table 1, and is similar to that described by Cocker et al. ( 2001a). Particle size distributions are obtained using a scanning electrical mobility spectrometer ( SEMS) ( Wang and Flagan, 1990) equipped with a 3077 85Kr charger, a 3081L cylindrical long column, and a 3760A condensation particle counter ( CPC).

Flow rates of 2.5 LPM and 0.25 LPM for sheath and aerosol flow, respectively, are maintained using Labview 6.0 assisted PID control of MKS proportional solenoid control valves and relating flow rate to pressure drop monitored by Honeywell pressure transmitters. Both the sheath and aerosol flow are obtained from the reactor enclosure. The data inversion algorithm described by Collins et al ( 2001) converts CPC counts versus time to number distribution. In addition, a tandem differential mobility analyzer ( TDMA) is available to measure physical changes to aerosol withdrawn from the chamber due to chemical or physical ( temperature)

changes in its environment ( Cocker et al, 2001a).

Characterization Results Light Characterization Photolysis rates used when modeling chamber experiments are calculated using the measured NO2 photolysis rates, the relative measured spectral distributions for the light sources, 8 and the absorption cross sections and quantum yields for NO2 and the other photolysis reactions in the chemical mechanism being evaluated. Therefore the measured NO2 photolysis rates serve as the measure of the absolute light intensity, and the relative spectral distributions of the light sources serve as the means to calculate the other photolysis rates relative to that for NO2. The precisions of the photolysis rates so derived are determined primarily by the precision of the NO2 actinometry measurement. These are described below.

Argon arc lamp Although the intensity of the argon arc light can be varied by varying the lamp power,

normally it is operated at 57% power, including all the experiments discussed here. Information about trends in light intensity with time is available from data from the spectral radiometer and PAR radiation instruments ( Table 1), and from results of NO2 actinometry experiments carried out periodically using the quartz tube method of Zafonte et al ( 1977) modified as discussed by Carter et al ( 1995a). The results indicated no significant change of light intensity with time during the period the chamber has been operated. Experiments with the quartz tube located inside the reactors yielded an NO2 photolysis rate of 0.26 ± 0.01 min 1.

The relative spectrum of the arc light source was measured using a LI COR LI 1800 spectroradiometer, and is shown on Figure 2. ( The data are normalized to the same NO2 photolysis rate because that is how they are used to derive photolysis rates in the experiments.

The instrument does not measure the spherically integrated absolute intensities needed to directly calculate photolysis rates, but its data are useful for relative measurements.) No appreciable change in the light source spectrum was observed in the first 18 months of operation.

Blacklamps A series of NO2 actinometry measurements inside the reactors with blacklight irradiation were carried out in April May of 2003 and again in October of that year, and the averages of the results were 0.19 and 0.18 min 1, respectively. Relative light intensity data taken during blacklight experiments indicated a gradual decreasing trend in light intensity during the experiments that was consistent with the differences between these two measurements. This gradual decrease in intensity with time is consistent with our experience with other blacklight 9 chambers ( e. g., see Carter et al, 1995a). The uncertainty in the NO2 photolysis rate assignments are estimated to be ~ 5%. The spectrum of this light source was essentially the same as that recommended by Carter et al ( 1995a) for modeling blacklight chamber runs, as shown in Figure 1, and did not change with time.

Characterization of Contamination by Outside Air Minimizing contamination of the reactor by leaks and permeation of laboratory air contaminants was an important design goal of the new reactors. This is accomplished by providing clean air within the enclosure that houses the reactors. Continuous monitoring of the enclosure contents demonstrates that NOx and formaldehyde levels in the enclosure before or during irradiations are less than 5 ppb and PM concentrations are below the detection limits of our instrumentation ( see Table 1). Introduction of contaminants into the reactor is also minimized by use of pressure control to assure that the reactors are always held at slight positive pressures with respect to the enclosure. Thus leaks are manifested by reduction of the reactor volume rather than dilution of the reactor by enclosure air. The leak rate into the chamber was tested by injecting ~ 100 ppm of CO into the enclosure and monitoring CO within the reactor for more than 6 hours. In addition, since CO is a small molecule, it should provide an upper limit of leak plus permeation into the reactor. No appreciable CO ( above the 50 ppb detection limit) was obtained for this experiment. Therefore it was concluded that leaks/ permeation into the chamber is negligible for the current reactor configuration.

Chamber Effects Characterization It is critical to understand the impact of reactor walls on gas phase reactivity and secondary aerosol formation. Larger volume reactors may minimize these effects, but they cannot be eliminated entirely or made negligible. For mechanism evaluation and SOA studies the most important of these effects include background offgasing of NOx and other reactive species,

offgasing or heterogeneous reactions that cause " chamber radical sources" upon irradiation ( e. g.,

see Carter et al, 1982), ozone and particle losses to the reactor walls, and background offgasing of PM or PM precursors. Most of these can be assessed by conducting various types of characterization experiments that either directly measure the parameter of interest, or are highly 10 sensitive to the chamber effect being assessed ( e. g., see Carter et al, 1995a). The chamber effects relevant to gas phase mechanism evaluation that have been assessed and the types of experiments utilized for assessing them are summarized in Table 2. These are discussed further below.

Note that as indicated in Table 2 some of the chamber characterization parameters are derived by conducting model simulations of the appropriate characterization experiments to determine which parameter values best fit the data. All the characterization simulations discussed here were carried out using the SAPRC 99 chemical mechanism ( Carter, 2000) with the photolysis rates calculated using the light characterization data discussed above, using the measured temperatures of the experiments, and assuming no dilution for reasons discussed in the previous section. The rates of heterogeneous reactions not discussed below, such as N2O5 hydrolysis to HNO3 or NO2 hydrolysis to HONO, were derived or estimated based on laboratory studies or other considerations as discussed by Carter et al ( 1995a). Although the assumed values of these parameters can affect model simulations under some conditions, they are not considered to be of primary importance in affecting simulations of the characterization or other experiments discussed here.

NOx offgasing NOx offgasing is the main factor limiting the utility of the chamber for conducting experiments under low NOx conditions. Although this can be derived by directly measuring increases in NOx species during experiments when NOx is not injected, the most sensitive measure is the formation of O3 in irradiations when VOCs but not NOx are initially present.

Therefore, the NOx offgasing rate is not determine directly, but derived by determining the magnitude of the NOx offgasing rates that it is necessary to assume in the chamber effects model for the model simulations of the experiments to correctly predict the experimentally observed O3 yields. The NOx offgasing can be represented in the model as inputs of any species that rapidly forms NOx in atmospheric irradiation systems, such as NO, NO2, or HONO ( which rapidly photolyzes to form NO, along with OH radicals), but for reasons discussed below it is represented in our chamber effects model as offgasing of HONO, e. g.,

Walls + h    HONO Rate = k1 x RN ( 1) 11 Where k1 is the light intensity as measured by the NO2 photolysis rate, and RN is the NOx ( and radical) offgasing parameter, which is derived by model simulations of the appropriate characterization experiments to determine which value best fits the data.

The NOx offgasing rates necessary to use in the model simulations to predict the observed O3 formation rates in the CO  air, formaldehyde  air and CO  formaldehyde  air experiments carried out in the first eight months of operation of this chamber are shown as the triangle symbols in Figure 3. The plots are against the EPA chamber experimental run number, which indicates the order that the experiment was carried out. It can be seen that the rates of around 1.5 ppt/ min generally fit the data up to around run 85, then these increased to 2 7 ppt/ min after that,

being somewhat higher in the " A" reactor compared to the " B" reactor. The reason for this increase is unclear, but it may be related to the fact that maintenance was done to the reactors around the time of the change. The magnitudes of these apparent NOx offgasing rates are discussed further below in conjunction with the discussion of the continuous radical source,

which is also attributed to HONO offgasing.

Chamber radical source It has been known for some time that environmental chamber experiments could not be modeled consistently unless some sources of radicals attributed to chamber effects is assumed ( e. g., Carter et al, 1982; Carter and Lurmann, 1991; Carter, 2000). The most sensitive experiments to this effect are NOx  air irradiations of compounds, such as CO or alkanes, which are not radical initiators or do not form radical initiating products to a sufficient extent to significantly affect their photooxidations. If no chamber dependent radical source is assumed,

model simulations of those experiments predict only very slow NO oxidation and essentially no O3 formation, while in fact the observed NO oxidation and O3 formation rates are much higher ( Carter et al, 1982). It is necessary to assume unknown or chamber dependent radical sources for the model to appropriately simulate the results of these experiments.

In some chambers at least part of the chamber dependent radical source can be attributed to formaldehyde offgasing ( Simonaitis et al, 1997, Carter, 2004), but as discussed below the magnitude of the formaldehyde offgasing in this chamber is relatively small, and not sufficient 12 by itself for the model to simulate radical source dependent experiments. For this chamber,

assuming HONO offgasing at a similar magnitude as the apparent NOx offgasing rate derived as discussed above is usually sufficient to account for most of the chamber dependent radical source, though results of some of the experiments are somewhat better simulated if a small amount ( 100 ppt or less) of HONO is also assumed to be initially present.

The round symbols in Figure 3 shows plots of the HONO offgasing rates that are necessary to assume in the model simulations for the model to simulate the NO oxidation and O3 formation rates in the radical source sensitive CO  NOx and n butane  NOx experiments that were carried out in January October of 2003. Note that since these experiments had initial NOx levels ranging from 10  200 ppb, so they were not sensitive to NOx offgasing as such. However,

from Figure 3 it can be seen that the magnitudes of the NOx offgasing and continuous radical input rates that fit the data for the respective characterization experiments were in the same range, and even changed at the same time when the characteristics of the chamber apparently changed. Whatever effect or contamination caused the apparent NOx offgasing to increase around the time of run 85 caused the same increase in the apparent radical source.

Comparison of Radical Source and NOx Offgasing with Other Chambers Although HONO is not measured directly in our experiments, the fact that both the radical sensitive and NOx sensitive characterization experiments can be simulated assuming HONO offgasing at approximately the same rates is highly suggestive that this is the process responsible for both effects. Direct evidence for this comes from the data of Rohrer et al ( 2004),

who used sensitive long path absorption photometer ( LOPAP) instrument to detect ppt levels of HONO emitted from the walls during irradiations in the large outdoor SAPHIR chamber ( Brauers et al, 2003) at rates comparable to those observed in the earlier experiments in our chamber. The SAPHIR chamber is similar in design to our chamber, except it is larger in volume and is located outdoors. In particular, like our chamber it has Teflon walls and uses an enclosure configuration to minimize contamination by outside air. Therefore, it would be expected to have similar chamber NOx and radical sources, and this appears to be the case. 13 Figure 4 shows plots of the NOx offgasing or radical source parameter ( e. g. RN in Equation 1) obtained in modeling appropriate characterization runs in various chambers, where they are compared with direct measurements made in the SAPHIR chamber ( Rohrer et al, 2004).

In addition to those for this UCR EPA, the radical source parameters shown are those derived by Carter ( 2000) for previous indoor and outdoor chambers at UCR ( Carter et al, 1995a), those derived by Carter and Lurmann ( 1991) for the University of North Carolina ( UNC) outdoor chamber ( Jeffries et al, 1982, 1995a c, 1990), and those derived by Carter ( 2004) for the Tennessee Valley Authority ( TVA) indoor chamber ( Simonaitis and Bailey, 1995; Bailey et al,

1996). ( Note that the data shown for the UCR EPA chamber includes experiments carried out subsequently to those shown in Figure 3, including a few runs at reduced temperature.) The figure shows that the radical source and NOx offgasing rates derived for this chamber are comparable in magnitude to the HONO offgasing directly measured in the SAPHIR chamber and also comparable to the NOx offgasing derived for TVA chamber but are significantly lower than those derived from modeling characterization data from the earlier UCR and UNC chambers. It is interesting to note that parameters derived for the various chambers indicate that the radical source and HONO or NOx offgasing rates all increase with temperature.

Therefore, the radical source and NOx offgasing rates indicated by the characterization data for the first series of experiments for this chamber is probably as low as one can obtain for reactors constructed of FEP Teflon film, which is generally believed to be the most inert material that is practical for use as chamber walls. Although the radical source and NOx offgasing rates for the second series of experiments is higher ( see also Figure 3), they are still about an order of magnitude lower than observed for the UCR and UNC chambers previously used for mechanism evaluation.

Formaldehyde offgasing Low but measurable amounts of formaldehyde were formed in irradiations in this chamber, even in pure air, CO  NOx, or other experiments where no formaldehyde or formaldehyde precursors were injected, and where formaldehyde formation from the reactions of methane in the background air is predicted to be negligible. The data in essentially all such experiments could be modeled assuming a continuous light dependent formaldehyde offgasing 14 rate corresponding to 0.3 ppb/ hour at the light intensity of these experiments. Formaldehyde levels resulting from this relatively low offgasing rate could not be detected with formaldehyde analyzers used in most previous UCR and other chamber experiments, and are insufficient to account for the apparent chamber radical source observed in most chamber experiments. This apparent formaldehyde offgasing has a non negligible effect on very low VOC and radical source characterization experiments, so it must be included in the chamber characterization model. However, it has a relatively minor impact on modeling most experiments used for VOC mechanism evaluation or reactivity assessment.

The source of the apparent formaldehyde offgasing in the Teflon reactors is unknown, but it is unlikely to be due to buildup of contaminants from previous exposures or contamination from the enclosure. The apparent formaldehyde offgasing rate is quite consistent in most cases and there are no measurable differences between the two reactors. This is despite the fact that the East or " Side B" reactor was constructed several months after the West or " Side A" reactor,

which was used in at least 17 experiments before the second reactor was built. In addition the background formaldehyde level in the enclosure was quite variable during this period, and no apparent correlation between this and the apparent formaldehyde offgasing rates in the reactor was observed. The data are best modeled by assuming only direct formaldehyde offgasing, as opposed to some formaldehyde being formed from light induced reactions of some undetected contaminant.

Other Reactive VOC Background or Offgasing Because of limitations in the detection and sensitivity of the organic monitoring methods currently available with our chamber, characterization experiments that are sensitive to background reactive VOCs provide the most useful means to assess whether background levels or offgasing of other reactive VOCs are significant. Ozone formation in pure air runs is very sensitive to background reactive VOCs, though it is also sensitive to the NOx offgasing effects discussed above. The average 6 hour ozone levels in the pure air runs carried out with the arc lights during this period with the chamber in the standard configuration was only 4 ± 2 ppb. This can be compared with the model simulations of the same experiments, using the NOx and formaldehyde offgasing parameters derived from the other characterization experiments as 15 discussed above, and assuming no other reactive VOCs are present, which gave an average 6

hour O3 of 6 ± 2 ppb. This indicates that background or offgasing of other reactive VOCs is not significantly affecting results of these experiments, and should have even smaller effects on mechanism evaluation experiments with added reactive VOCs.

Particle wall losses Particle wall losses are expected in finite volume reactors and are somewhat enhanced by the charged surfaces of the Teflon media. Particle wall losses within chambers have been described in detail in Cocker et al. ( 2001a). Briefly, wall losses are expected to be described by a first order wall loss mechanism with a weak size dependence for the aerosol sizes typical of SOA experiments. Particle wall loss rates can be determined in any experiment where particles are present for a sufficiently long time that new particle formation is no longer determining. If it is assumed that no new particle formation is occurring, then the decay rate in the particle number can be assumed to be the particle loss rate.

Figure 5 shows plots of particle wall loss obtained from data from various experiments in this chamber from the time particle measurements were made through the summer of 2004. It can be seen that although there is run to run variability, the decay rates are reasonably consistent at approximately 7 day 1, with no significant differences among reactors. This is within the range reported for other large chamber facilities ( Barnes and Sidebottom, 2000, Griffin, 1999). While the maximum particle volume in the experiments ranged from less than 0.1 to almost 80 µ g/ m3,

there was no correlation between maximum particle volume and measured decay rate.

Background Particle Formation The reactor walls could be a source of particles as well as gas phase species. This could be due to either direct release of particles from the walls during the irradiations, or offgasing of compounds that react to form secondary PM. Background PM formation could also occur if there were impurities in the air that reacted to form secondary PM. This would be manifested by the formation of particles in pure air irradiations or irradiations of reactants that are not expected to form condensable products. 16 Maximum PM number and PM volume levels measured after 5 hours of irradiation in pure air, CO  air, CO  NOx  air, and propene  NOx experiments carried out in the second set of reactors, installed immediately before run 169, are shown on Figure 6. ( Characterization data for the first set of reactors are sparse but generally consistent with the results shown here.)

Measurable PM formation is seen in pure air and propene  NOx experiments, but essentially no PM formation is seen in the CO  air or CO  NOx irradiations. The lack of measurable PM in the CO  air or CO  NOx experiments suggests that PM is not directly emitted from the irradiated walls, though this is considered to be unlikely in the first place. The fact that background PM is formed in the pure air and propene  NOx experiments but not the CO  air or CO  NOx experiments could be attributed to PM formation from the reaction of OH radicals with some background contaminant( s). Model calculations predict that OH levels are suppressed in the CO experiments because of its reaction with CO combined with the lack of homogeneous radical sources in CO  air or CO  NOx systems.

The background PM in the pure air and propene  NOx experiments is the highest when the rectors were new, and eventually decline as the reactor is used. This suggests that, at least for these reactors, contaminants due to the experiments are less important than contaminants on the new Teflon film or that are introduced during its construction. The apparent background PM in eventually declined in both reactors, becoming very low in Reactor B, but continued to be nonnegligible in Reactor A. Reactor A also had higher levels of background PM at the start.

Although the reaction of O3 with background contaminants could be another source of background PM, this does not appear to be as significant in this chamber. Higher levels of O3 are formed in CO  air than in pure air runs, yet the PM levels are much lower in the presence of CO.

PM levels in O3 dark decay experiments are relatively low. In particular, the PM volume in the 0.2 ppm O3 dark decay experiment 179 was only ~ 0.1 µ g/ m3 in both reactors after ~ 5 hours,

despite the fact that this was during period with new reactors when the background was relatively high. The PM levels increased only slightly when O3 was irradiated. 17 Initial Experiments Gas Phase Characterization and Mechanism Evaluation Experiments Table 3 gives a summary of the initial experiments carried out in this chamber for gasphase characterization and mechanism evaluation. All these experiments were carried with unhumidified air ( dew point <  40 C), at atmospheric pressure (~ 740 torr local pressure) and at 303 ± 1 K for arc light runs and at 301 ± 1 K for blacklight experiments. The various characterization experiments were used to derive the chamber characterization parameters and evaluate the chamber characterization model as discussed above. The single organic  NOx experiments were carried out to demonstrate the utility of the chamber to test the mechanisms for these compounds, for which data are available in other chambers, and to obtain wellcharacterized mechanism evaluation data at lower NOx levels than previously available. The formaldehyde + CO  NOx experiments were carried out because they provided the most chemically simple system that model calculations indicated was insensitive to chamber effects,

to provide a test for both the basic mechanism and the light characterization assignments. The aromatic + CO  NOx experiments were carried out because aromatic  NOx experiments were predicted to be very sensitive to the addition of CO, because it enhances the effects of radicals formed in the aromatic system on ozone formation. The ambient surrogate  NOx experiments were carried out to test the ability of the mechanism to simulate ozone formation under simulated ambient conditions at various reactive organic gas ( ROG) and NOx levels.

The ROG surrogate used in the ambient surrogate  NOx experiments consisted of a simplified mixture designed to represent the major classes of hydrocarbons and aldehydes measured in ambient urban atmospheres, with one compound used to represent each model species used in condensed lumped molecule mechanism. The eight representative compounds used were n butane, n octane, ethene, propene, trans 2 butene, toluene, m xylene, and formaldehyde. ( See Carter et al, 1995c, for a discussion of the derivation of this surrogate).

The ability of the SAPRC 99 mechanism ( Carter, 2000) to simulate the total amount of NO oxidized and O3 formed in the experiments, measured by ([ O3] final[ NO] final)  ([ O3] initial

[ NO] initial), or  ([ O3][ NO]), is summarized for the various types of experiments on Table 3 and shown for the individual runs on Figure 7. This gives an indication of the biases and run to run 18 variability of the mechanism in simulating ozone formation. In experiments with excess NO the processes responsible for O3 formation are manifested by consumption of NO, so simulations of  ([ O3][ NO]) provides a test of model simulations of these processes even for experiments where O3 is not formed.

Note that the characterization runs were modeled using the same set of characterization parameters as used when modeling the mechanism evaluation runs, which are based on averages of best fit values for the individual experiments, and not with the values that were adjusted to fit the individual runs. Therefore, the relatively large variability and average model error for the model simulations of  ([ O3][ NO]) in those experiments provides a measure of the variability of the chamber effects parameters ( e. g., HONO offgasing) to which these experiments are sensitive.

The relatively low average bias is expected because the chamber effects parameter values were derived based on these data.

For the single VOC  NOx or VOC  CO  NOx experiments, the model is able to simulate the  ([ O3][ NO]) to within ± 25% or better in most cases, which is better than the ± ~ 30% seen in previous mechanism evaluations with the older chamber data ( Carter and Lurmann, 1990, 1991;

Gery et al, 1989, Carter, 2000). However, there are indications of non negligible biases in model simulations of certain classes of experiments. The cleaner conditions and the relatively lower magnitude of the chamber effects may make the run to run scatter in the model performance less than in the simulations of the previous data, and this tends to make smaller biases in the model performance more evident. For example, Figure 7 shows that the mechanism tends to underpredict O3 formation in aromatic  NOx experiments with added CO, even though it has a slight tendency to overpredict O3 in the aromatic  NOx experiments without added CO. This suggests problems with the aromatics mechanisms that need further investigation ( Carter, 2004).

The mechanism tended to have a bias towards underpredicting  ([ O3][ NO]) in the ambient surrogate  NOx experiments, though as indicated in Figure 7 this underprediction did not occur for all experiments. The underprediction bias had very little correlation with the initial ROG and NOx levels in the experiments but was highly correlated with the initial ROG/ NOx ratio. This is shown in Figure 8, which gives plots of the  ([ O3][ NO]) model underprediction 19 bias against the initial ROG/ NOx ratio the experiments. The " error bars" show the effects of varying the HONO offgasing parameter over the extreme values shown in Figure 4 for this chamber for the 303 ± 1 K temperature range, which applicable to these experiments. It can be seen that the model has a definite tendency to underpredict  ([ O3][ NO]) at the low ROG/ NOx ratios. Although the HONO offgasing parameter has a non negligible effect on the simulations of the experiments at the lowest and highest ROG/ NOx ratio ( because of sensitivities to the radical source in the first case and to the NOx source in the second), the sensitivity is not sufficient to account to the trend in the bias with ROG/ NOx. This trend was not evident in the previous mechanism evaluations, perhaps in part because of the greater variabilities of the model simulations due to greater chamber effects or characterization uncertainties, and perhaps in part because this is not as evident at higher reactant concentrations. This suggests problems with the mechanism that also needs further investigation ( Carter, 2004).

As indicated in Table 3, the initial evaluation experiments included runs with NOx levels as low as 2 5 ppb, which is considerably lower than in experiments used previously for mechanism evaluation. Most of the experiments used in the previous SAPRC 99 mechanism evaluation had NOx levels greater than 50 ppb, and even the " low NOx" TVA and CSIRO experiments had NOx levels of ~ 20 ppb or greater, except for a few characterization runs ( Carter,

2004, and references therein). However, other than the ROG/ NOx effect for the ambient surrogate experiments discussed above, there is no indication in any difference in model performance in simulating the results of these very low NOx experiments, compared to those with the higher NOx levels more representative of those used in the previous evaluation. This is an important finding because there has been a concern about using mechanisms evaluated at higher than ambient NOx levels for ambient simulations of remote areas or future case attainment scenarios ( Dodge, 2000).

For example, Figure 9 shows concentration time plots for selected measured species in ambient surrogate  NOx experiment carried out at the lowest NOx levels in the initial evaluation runs. To indicate the sensitivity of the experiments to NOx offgasing effects, the effects of varying the HONO offgasing parameter from zero to the maximum level consistent with the characterization experiments is also shown. It can be seen that the model using the default 20 HONO offgasing parameter value gives very good fits to the data. Although the O3 simulations are somewhat affected when the HONO offgasing rate is varied within this somewhat extreme range, the sensitivity is not so great that the uncertainty in this parameter significantly affects conclusions one can draw about the ability of the model to simulate this low NOx experiment.

However, the sensitivity would increase as the NOx levels are reduced, and ~ 2 ppb NOx probably represents a reasonable lower limit for NOx levels useful for mechanism evaluation.

Overall, the results of the initial characterization and evaluation indicate that this chamber can provide high quality mechanism evaluation data for experiments with NOx levels as low as ~ 2 ppb, considerably lower than employed in previous experiments. Chamber effects are not absent, but they are as low or lower than in observed in any previous chambers used for mechanism evaluation, in some cases by an order of magnitude or more. Although a larger number of experiments would be required to fully assess this, the results also suggest a higher degree of precision in mechanism evaluation than observed previously, making smaller biases in mechanism performance more evident. The initial dataset from this chamber indicate no significant problems with mechanism performance that are characteristic of low NOx conditions as such, but do reveal problems with the mechanisms for aromatics and the ambient ROG surrogate ( Carter, 2004).

m Xylene NOx SOA Yield A series of m xylene/ NOx experiments photooxidations were performed using the blacklights as an irradiation source. These blacklight experiments were carried with unhumidified air ( dew point <  40 C), at atmospheric pressure (~ 740 torr local pressure) and at at 301 ± 1 K. These experiments were used to determine our ability to perform SOA experiments.

The data is analyzed following the original schemes outlined by Pankow et al. ( 1994a, b) and Odum et al. ( 1996). Briefly, SOA yield, Y, is defined as the ratio of aerosol ( µ g m 3) to hydrocarbon reacted ( µ g m 3).

  +     = =

i org i om, i om, i org i i M     M Y Y 1 ( 2) 21 where  i is the mass based stoichiometric fraction of species i formed from the parent hydrocarbon, Kom, i is the gas particle partitioning coefficient ( m3 µ g 1), which is inversely proportional to the compound's vapor pressure, and   Morg ( µ g m 3) is the total mass concentration of organic material and associated water present in the aerosol phase. The fraction of secondary organic material condensing into the aerosol phase is seen to depend on the amount of organic aerosol mass present. The two product semi empirical model then assumes that two surrogate species can be used to estimate the SOA yield: one surrogate product representing low vapor pressure compounds and one surrogate product representing high vapor pressure compounds. ( i= 1,2 in equation 2)

A set of characterization runs was carried out to demonstrate the ability of the chamber to perform SOA formation experiments. M xylene was chosen as the initial test compound. Four experiments with initial m xylene and NO initial concentrations of 75 ppb and 50 ppb respectively, T= 300K, no initial aerosol present, and blacklight irradiation source were conducted until measurable aerosol volume growth ( corrected for wall loss) had ceased ( approximately 8 hours irradiation time, ~ 90% m xylene consumption). The experiments were conducted on both reactors with a couple of months time separating the first and last experiment.

Average total aerosol production for the four reactions was 21.4 ± 0.3 µ g m 3.

Additional m xylene/ NOx experiments were performed with blacklights for comparison to previously published yield data. The yield data are most easily compared to recent m xylene irradiations at Caltech at comparable experimental conditions ( indoors, blacklight source, similar temperatures) ( Cocker et al. 2001c), and the results for the various chambers are shown on Figure 10. The " Empirical Fit through UCR Data" is the the best fit two product semi empirical fit yield curve for the current dataset from this chamber, for which the parameters are 0.075,

0.105, 0.139, 0.010 for  1,  2,  om, 1,  om, 2, respectively. The overall agreement between this chamber and the Caltech chamber helps to verify the ability of the new chamber to accurately simulate gas to particle conversion processes. More details on the current dataset for mxylene NOx aerosol production can be found in Song et al. ( 2005). 22 Discussion and Conclusions This chamber facility was designed to provide more precise and comprehensive mechanism evaluation data, and at lower simulated pollutant concentrations, than previously possible. Although the dataset from this chamber is still limited, the results to date demonstrate its utility for providing valuable data for mechanism evaluation. The major background effects parameters in the chamber appear to be lower than those observed in other chambers used for mechanism evaluation, including the TVA chamber, which was also designed for experiments at lower pollution levels ( Simonaitis and Bailey, 1995; Simonaitis et al, 1997).

The lower background levels in this chamber permitted successful mechanism evaluation experiments to be carried out with NOx levels as low as 2 ppb. This is at least an order of magnitude lower than in the mechanism evaluation dataset from other chambers used for gasphase mechanism evaluation. In addition, we believe that the lower background effects attainable in this chamber provided an improvement in the precision of the mechanism evaluation dataset.

The results of modeling the relatively large number of surrogate  NOx experiments give some information regarding this. Although the model had systematic biases in simulating many of these experiments, as shown in Figure 8, plots of model biases against ROG/ NOx ratios had relatively little scatter, suggesting fits to within ± 10% could be obtained if the current problem( s)

with the mechanism can be corrected. This is less than the scatter for the fits to comparable experiments in other chambers ( Carter and Lurmann, 1991; Carter, 2000, 2004). This is important since if the scatter in these fits were on the order of ± 30%, which was observed mechanism evaluation studies using other chamber data sets ( e. g., Carter and Lurmann, 1991),

the ROG/ NOx dependences may not have been statistically significant, and the mechanism performance would have been concluded to be satisfactory. With this more precise dataset the low ROG/ NOx problem with the mechanism is evident.

We believe that this chamber is also well suited for studies of secondary aerosol formation. The good reproducibility of multiple experiments and general agreement with past work demonstrates our ability to accurately and precisely measure SOA formation potentials. 23 Further work is clearly needed to characterize and eventually reduce or control background aerosol formation in this chamber, though this appears to be a problem with all environmental chambers used for aerosol studies. The relatively low chamber background effects and degree of characterization for gas phase processes is also a significant advantage in studies of secondary PM formation, since it is the gas phase processes that lead to the formation of secondary PM.

The ability to control temperature ( and therefore humidity) is important, since data are needed to systematically study gas to particle conversion processes in well controlled reactors.

Although the experiments reported here were carried only under dry conditions and at a single temperature, a humidification system has been constructed and the chamber is capable of controlled experiments in a wide temperature range of relevance to tropospheric pollution.

Experiments to assess effects of varying humidity and temperature will be discussed in subsequent papers.

Acknowledgements The construction and initial characterization of this facility was funded by the United States Environmental Protection Agency Cooperative Agreement No. CR 827331 01. Some of the later experiments were also funded through EPA Cooperative Agreement No. CR 830957

01, Gail Tonnesen, Principal Investigator, and the lowest NOx surrogate experiments were funded by California Air Resources Board Contract 01 305. Additional funding from NSF grant no. 024111 is also acknowledged. Helpful discussions with Dr. Basil Dimitriades and Deborah Luecken, the EPA project officers, are acknowledged. Assistance in the design and construction of this facility was provided by Mr. Matthew Smith. Dr. Joseph Norbeck provided valuable assistance in developing the necessary infrastructure to house this facility. 24 References Bailey, E. M., C. H. Copeland and R. Simonaitis ( 1996): " Smog Chamber Studies at Low VOC and NOx Concentrations," Report on Interagency Agreement DW64936024 to EPA/ NREL, Research Triangle Park, NC.

Barnes, I. and H. Sidebutton ( 2000). The European Photoreactor, 3rd report, 2000. Available at http:// www. physchem. uni wuppertal. de/ PC WWW_ Site/ pub/ Projektberichte/ EUPHORE _ 2000_ final. pdf.

Brauers, T., B. Bohn, F. J. Johnen, F. Rohrer, S. Rodriguez Bares, R. Tillmann, and A. Wahner ( 2003): " The Atmosphere Simulation Chamber SAPHIR: a Tool for the Investigation of Photochemistry," Presented at the EGS  AGU  EUG Joint Assembly, Nice, France, April 11, 2003. See also http:// www. fz juelich. de/ icg/ icg ii/ saphir/ home.

Carter, W. P. L. ( 2000): " Documentation of the SAPRC 99 chemical mechanism for VOC reactivity assessment," Report to the California Air Resources Board, Contracts 92 329 and 95 308, May 8 ( 2000). Available at http:// www. cert. ucr. edu/~ carter/ absts. htm # saprc99.

Carter, W. P. L. ( 2004): " Evaluation of a gas phase atmospheric reaction mechanism for low NOx conditions," Final Report to California Air Resources Board Contract No. 01 305, May 5. Available at http:// www. cert. ucr. edu/~ carter/ absts. htm# lnoxrpt.

Carter, W. P. L., R. Atkinson, A. M. Winer, and J. N. Pitts, Jr. ( 1982): " Experimental Investigation of Chamber Dependent Radical Sources," Int. J. Chem. Kinet., 14, 1071.

Carter, W. P. L. and F. W. Lurmann ( 1991): " Evaluation of a Detailed Gas Phase Atmospheric Reaction Mechanism using Environmental Chamber Data," Atm. Environ. 25A, 2771 2806.

Carter, W. P. L., and F. W. Lurmann ( 1990): " Evaluation of the RADM Gas Phase Chemical Mechanism," Final Report, EPA 600/ 3 90 001.

Carter, W. P. L., D. Luo, I. L. Malkina, and D. Fitz ( 1995a): " The University of California, Riverside Environmental Chamber Data Base for Evaluating Oxidant Mechanism. Indoor Chamber Experiments through 1993," Report submitted to the U. S. Environmental Protection Agency, EPA/ AREAL, Research Triangle Park, NC., March 20. Available at http:// www. cert. ucr. edu/ ~ carter/ absts. htm# databas. 25 Carter, W. P. L., D. Luo, I. L. Malkina, and J. A. Pierce ( 1995b): " Environmental Chamber Studies of Atmospheric Reactivities of Volatile Organic Compounds. Effects of Varying Chamber and Light Source," Final report to National Renewable Energy Laboratory, Contract XZ 2 12075, Coordinating Research Council, Inc., Project M 9, California Air Resources Board, Contract A032 0692, and South Coast Air Quality Management District, Contract C91323, March 26. Available at http:// www. cert. ucr. edu/~ carter / absts. htm# explrept.

Carter, W. P. L., D. Luo, I. L. Malkina, and J. A. Pierce ( 1995c); " Environmental chamber studies of atmospheric reactivities of volatile organic compounds. Effects of varying ROG surrogate and NOx," Final report to Coordinating Research Council, Inc., Project ME 9, California Air Resources Board, Contract A032 0692, and South Coast Air Quality Management District, Contract C91323. March 24. Available at http:// www. cert. ucr. edu/~ carter/ absts. htm# rct2rept.

Carter, W. P. L. ( 2004): " Evaluation of a Gas Phase Atmospheric Reaction Mechanism for Low NOx Conditions," Final report to the California Air Resources Board for Contract 01 305, May 5. Available at http:// www. cert. ucr. edu/~ carter/ absts. htm# lnoxrpt Cocker, D. R., R. C. Flagan, and J. H. Seinfeld. ( 2001a). " State of the art chamber facility for studying atmospheric aerosol chemistry," Environ. Sci. Technol. 35, 2594 2601.

Cocker, D. R., S. L. Clegg, R. C. Flagan, and J. H. Seinfeld. ( 2001b). " The effect of water on gas particle partitioning of secondary organic aerosol. Part I: alpha pinene/ ozone system," Atmos. Environ, 35, 6049 6072.

Cocker, D. R., B. T. Mader, M. Kalberer, R. C. Flagan, and J. H. Seinfeld ( 2001c). " The Effect of Water on Gas Particle Partitioning of Secondary Organic Aerosol. II: m Xylene and 1,3,5 Trimethylbenzene Photooxidation Systems," Atmos. Environ. 35, 6073 6085.

Collins D. R., R. C. Flagan, and J. H. Seinfeld ( 2001). Improved inversion of scanning DMA data. In press. Aerosol Science Technology Dodge, M. C. ( 2000): " Chemical Oxidant Mechanisms for Air Quality Modeling, Critical Review Paper for 1998 Ozone Assessment," Atmos. Environ, 34, 2103 2130.

Gaffney, J. S, R. M. Bornick, Y H Chen, and N. A. Marley ( 1998): " Capillary gas chromatographic analysis of nitrogen dioxide and PANs with luminol chemiluminescent detection," Atmos. Environ. 32, pp. 1445 1454.

Gery, M. W., G. Z. Whitten, and J. P. Killus ( 1988): " Development and Testing of the CBM IV For Urban and Regional Modeling," EPA 600/ 3 88 012, January.

Griffin, R. J., D. R. Cocker, J. H. Seinfeld, D. Dabdub ( 1999) " Estimate of global atmospheric organic aerosol from oxidation of biogenic hydrocarbons," Geophysical research letters 26 ( 17): 2721 2724. 26 Griffin, R. J., D. Dabdub M. J. Kleeman, M. P. Fraser, G. R. Cass, and J. H. Seinfeld ( 2002). " Secondary organic aerosol  3. Urban/ regional scale model of size and compositionresolved aerosols," Journal of Geophysical Research Atmospheres 107 ( D17), Art. No. 4334.

Griffin, R. J., D. R. Cocker, R. C. Flagan, and J. H. Seinfeld ( 1999). " Organic aerosol formation from the oxidation of biogenic hydrocarbons," Journal of Geophysical Research Atmospheres 104 ( D3): 3555 3567.

Hastie, D. R, G. I. Mackay, T. Iguchi, B. A. Ridley, and H. I. Schiff ( 1983): " Tunable diode laser systems for measuring trace gases in tropospheric air," Environ. Sci. Technol. 17, 352A 364A.

Hess G. D., F. Carnovale. M. E., Cope. and G. M. Johnson ( 1992) " The evaluation of some photochemical smog reaction mechanisms   1 temperature and initial composition effects", Atmos. Environ., 26A, 625 641.

Holdren, M. W. and C. W. Spicer ( 1984): " Field Compatible Calibration Procedure for Peroxyacetyl Nitrate," Environ. Sci. Technol., 18, 113 115.

Jacobsen, N. W. and R. G. Dickinson ( 1994): " Spectrometric Assay of Aldehydes as 6 Mercapto 3 substituted s triazolo( 4,3 b) s tetrazines," Analytical Chemistry 46/ 2 ( 1974) 298   299.

Jang M. S. and R. M. Kamens ( 2001): " Characterization of secondary aerosol from the photooxidation of toluene in the presence of NOx and 1 propene," Environmental Science & Technology 35 ( 18): 3626 3639.

Jaoui M., K. G. Sexton, and R. M. Kamens ( 2004): " Reaction of alpha cedrene with ozone: mechanism, gas and particulate products distribution," Atmospheric Environment 38 ( 17): 2709 2725.

Jeffries, H. E., R. M. Kamens, K. G. Sexton, and A. A. Gerhardt ( 1982): " Outdoor Smog Chamber Experiments to Test Photochemical Models", EPA 600/ 3 82 016a, April.

Jeffries, H. E., K. G. Sexton, R. M. Kamens, and M. S. Holleman ( 1985a): " Outdoor Smog Chamber Experiments to Test Photochemical Models: Phase II," Final Report, EPA 600/ 3 85 029.

Jeffries, H. E., K. G. Sexton, T. P. Morris, H. Jackson, R. G. Goodman, R. M. Kamens, and M. S. Holleman ( 1985b): " Outdoor Smog Chamber Experiments Using Automobile Exhaust," Final Report, EPA 600/ 3 85 032.

Jeffries, H. E., K. G. Sexton, and M. S. Holleman ( 1985c): " Outdoor Smog Chamber experiments: Reactivity of Methanol Exhaust", Final Report, EPA 600/ 3 85 009a, September 27 Jeffries, H. E., K. G. Sexton, J. R. Arnold, Y. Bei, J. L. Li, and R. Crouse ( 1990): " A Chamber and Modeling Study to Assess the Photochemistry of Formaldehyde," Report on EPA Cooperative Agreement 813964, Atmospheric Research and Exposure Assessment Laboratory, U. S. EPA, Research Triangle Park, NC.

Jeffries, H. E.; M. W. Gery, and W. P. L. Carter ( 1992) Protocol for evaluating oxidant mechanisms for urban and regional models. Report for U. S. Environmental Protection Agency Cooperative Agreement No. 815779, Atmospheric Research and Exposure Assessment Laboratory, Research Triangle Park, NC.

Johnson, D., Jenkin, M. E. Wirtz, K., and Montserrat, M R ( 2004). " Simulating the formation of secondary organic aerosol from the photooxidation of toluene environmental chemistry," Environ. Chem. 1, 150 165 Kleindienst, T. E., D. F. Smith, W. Li, E. O. Edney, D. J. Driscoll, R. E. Speer R, and W. S. Weathers ( 1999). " Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol," Atmospheric Environment 33 ( 22): 3669 3681.

Montserrat, M R, Wirtz, K ( 2005). " Is benzene an precursor for secondary organic aerosol?" Environ. Sci. Technol. 39, 1045 1054 NIOSH ( 1994): " Sulfite titration of formaldehyde stock solution: modified Method 3500," NIOSH Manual of Analytical Methods, NMAM, fourth edition, August 15.

Odum J. R., T. Hoffmann, F. Bowmam, D. Collins, R, C, Flagan, and J. H. Seinfeld ( 1996). " Gas/ particle partitioning and secondary organic aerosol yields," Environ. Sci. Technol. 30, 2580 2585.

Odum J. R., T. P. W. Jungkamp, R. J. Griffin, R. C. Flagan and J. H. Seinfeld ( 1997). " The atmospheric aerosol forming potential of whole gasoline vapor," Science 276 ( 5309): 96 99.

Pandis, S. N., R, A. Harley, G. R. Cass, and J. H. Seinfeld ( 1992). " Secondary organic aerosol formation and transport," Atmospheric Environment, 26( 13): 2269 2282.

Pankow, J. F. ( 1994). " An absorption model of gas/ particle partitioning of organic compounds in the atmosphere," Atmos. Environ. 28, 185 188.

Pankow, J. F. ( 1994), " An absorption model of the gas/ aerosol partitioning involved in the formation of secondary organic aerosol," Atmos. Environ. 28, 189 193.

Pun B. K., S. Y. Wu, C. Seigneur, J. H. Seinfeld, R. J. Griffin, and S. N. Pandis ( 2003). " Uncertainties in modeling secondary organic aerosols: Three dimensional modeling studies in Nashville/ Western Tennessee," Environmental Science & Technology, 37 ( 16): 3647 3661. 28 Quesenberry, M. S. and Y. C. Lee ( 1996): " A Rapid Formaldehyde Assay Using Puprald Reagent: Application under Periodation Conditions," Analytical Biochemistry. 234, 50   55.

Rohrer, F., Bohn, B., Brauers, T., Brüning, D., Johnen, F.  J., Wahner, A. and Kleffmann, J. ( 2004). " Characterisation of the photolytic HONO source in the atmosphere simulation chamber SAPHIR," Atmos. Chem. and Physics Disc., 4, 7881 7915 Seinfeld, J. H. and J. F. Pankow ( 2003). " Organic atmospheric particulate material," Annual review of Physical Chemistry 54: 121 140.

Schiff, H.. I., G. I. Mackay, and J. Bechara ( 1994): " The Use of Tunable Diode Laser Absorption Spectroscopy for Atmospheric Measurements", Res. Chem. Intermed. 20, 1994, pp 525 556.

Simonaitis, R. and E. M. Bailey ( 1995): " Smog Chamber Studies at Low VOC and NOx Concentrations: Phase I," Report on Interagency Agreement DW64936024 to EPA/ NREL, Research Triangle Park, NC.

Simonaitis, R., J. Meagher, and E. M. Bailey ( 1997): " Evaluation of the condensed Carbon Bond Mechanism against smog chamber data at low VOC and NOx Concentrations," Atm. Environ. 31, 27 43 Song, C., K. Na, and D. R. Cocker ( 2005). " Impact of hydrocarbon to NOx ratio on secondary organic aerosol formation", Environ. Sci. and Technol., 39, 3143 3149.

Stockwell, W. R., P. Middleton, J. S. Chang and X. Tang ( 1990): " The RADM2 Chemical Mechanism for Regional Air Quality Modeling," J. Geophys. Res., 95, 16343 16367.

Wang, S. C. and R. C. Flagan ( 1990) Scanning Electrical Mobility Spectrometer. Aerosol Science and Technology. 13( 2): 230 240 1990 Zafonte, L., P. L. Rieger, and J. R. Holmes ( 1977): " Nitrogen Dioxide Photolysis in the Los Angeles Atmosphere," Environ. Sci. Technol. 11, 483 487. 29 Table 1. List of analytical and characterization instrumentation Type Model or Description Species Sensitivity Comments Ozone Analyzer Dasibi Model 1003 AH. UV absorption analysis. Monitor Labs Chemiluminescence Ozone Analyzer Model 8410 O3 2 ppb Standard monitoring instruments.

NO 1 ppb NO  NOy Analyzer Teco Model 42 C with external converter. Chemiluminescent analysis for NO, NOy by catalytic conversion. NOy 1 ppb Useful for NO and initial NO2 monitoring. Converter close coupled to the reactors so the " NOy" channel should include HNO3 as well as NO2, PANs, organic nitrates, and other species converted to NO by the catalyst.

CO Analyzer Dasibi Model 48C. Gas correlation IR analysis. CO 50 ppb Standard monitoring instrument NO2 0.5 ppb NO2 data from this instrument are considered to be interference free. Tunable Diode Laser Absorption Spectroscopy ( TDLAS) # 1 HNO3 ~ 1 ppb HNO3 data were not available for all experiments discussed in this paper.

HCHO ~ 1 ppb Formaldehyde data from this instrument are considered to be interference free. TDLAS # 2 TDLAS analysis is based on measuring single rotational  vibrational lines in the near to mid infrared using tunable laser diodes with very narrow line widths ( Hastie et al., 1983; Schiff et al., 1994), Two such instruments purchased from Unisearch Inc. and adapted for this chamber. Data transmitted to DAC system using RS 232. H2O2 ~ 2 ppb H2O2 measurements were not made during the experiments discussed in this paper.

GC FID # 1 HP 5890 Series II GC with dual columns, loop injectors and FID detectors. Various megabore GC columns available. Controlled by computer interfaced to network. VOCs ~ 10 ppbC Equipped with: 30 m x 0.53 mm GSAlumina column used for the analysis of light hydrocarbons and 30 m x 0.53 mm DB 5 column used for the analysis of C5+ alkanes and aromatics. Loop injection suitable for low to medium volatility VOCs that are not too " sticky" to pass through valves.

VOCs ~ 10 ppbC 30 m x0.53 mm GSQ column. Loop injection suitable for low to medium volatility VOCs that are not too " sticky". Not used as primary analysis for most of these experiments. GC FID # 2 HP 5890 Series II GC with dual columns and FID detectors, one with loop sampling and one set up for Tenax cartridge sampling. Various megabore GC columns available. Controlled by computer interfaced to network. VOCs 1 ppbC Tenax cartridge sampling can be used for low volatility or moderately " sticky" VOCs that cannot go through GC valves but can go through GC columns. Equipped with a 30 m x 0.53 mm DB 1701 column.

Luminol GC Developed and fabricated at our laboratory based on work of Gaffney et al ( 1998). Uses GC to separate NO2 from PAN NO2 ~ 0.5 ppb NO2 measurements were found to have interferences by O3 and perhaps other species and may not be useful for quantitative mechanism evaluation. 30 Type Model or Description Species Sensitivity Comments and other compounds and Luminol detection for NO2 or PAN. Data transmitted to the DAC system using RS 232. PAN ~ 0.5 ppb Reliability of measurement for PAN not fully evaluated. Calibration results indicate about a 30% uncertainty in the spans. However, interferences are less likely to be a problem than for NO2.

Gas Calibrator Model 146C Thermo Environmental Dynamic Gas Calibrator N/ A N/ A Used for calibration of NOx and other analyzers. Instrument acquired early in project and under continuous use.

Data Acquisition Sytem Windows PC with custom LabView software, 16 analog input, 40 I/ O, 16 thermocouple and 8 RS 232 channels. N/ A N/ A Used to collect data from most monitoring instruments and control sampling solenoids. In house LabView software was developed using software developed by Sonoma Technology for ARB for the Central California Air Quality Study as the starting point.

Temperature sensors Various thermocouples, radiation shielded thermocouple housing Temperature ~ 0.1 oC Primary measurement is thermocouples inside reactor. Corrections made for radiative heating effect with arc light irradiation.

Humidity Monitor General Eastern HYGRO M1 Dew Point Monitor Humidity Dew point range:  40  50oC Dew point below the performance range for the unhumidified experiments discussed in this paper.

Spectroradiometer LiCor LI 1800 Spectroradiometer 300 850 nm Light Spectrum Adequate Resolution relatively low but adequate for its purpose. Used to obtain relative spectrum. Also gives an absolute intensity measurement on surface useful for assessing relative trends.

Spherical Irradiance Sensors Biospherical QSL 2100 PAR Irradiance Sensor or related product. Responds to 400 700 nm light. Spectral response curve included. Spherical Broadband Light Intensity Adequate Provides a measure of absolute intensity and light uniformity that is more directly related to photolysis rates than light intensity on surface. Gives more precise measurement of light intensity trends than NO2 actinometry, but is relatively sensitive to small changes in position.

Scanning Electrical Mobility Spectrometer ( SEMS) Similar to that described in Cocker et al. ( 2001a). See text Aerosol Number and Volume concentration Adequate Provides information on size distribution of aerosols in the 28 730 nm size range, which accounts for most of the aerosol mass formed in our experiments. Data can be used to assess effects of VOCs on secondary PM formation. 31 Table 2. Summary of types of characterization experiments and types of chamber effects parameters relevant to gas phase mechanism evaluation derived from these experiments.

Run Type No. Runs Sensitive Parameters Comments Ozone Dark Decay 4 O3 wall loss rate The loss of O3 in the dark is attributed entirely to a unimolecular wall loss process.

CO  Air 8 NOx offgasing Insensitive to radical source parameters but O3 formation is very sensitive to NOx offgasing rates. Formaldehyde data can also be used to derive formaldehyde offgasing rates.

CO  HCHO  air 2 NOx offgasing. Insensitive to radical source parameters but O3 formation is very sensitive to NOx offgasing rates. Also can be used to obtain formaldehyde photolysis rates CO  NOx 6 Initial HONO, Radical source O3 formation and NO oxidation rates are very sensitive to radical source but not sensitive to NOx offgasing parameters. Formaldehyde data can also be used to derive formaldehyde offgasing rates.

n Butane  NOx 1 Initial HONO, Radical source O3 formation and NO oxidation rates are very sensitive to radical source but not sensitive to NOx offgasing parameters.

Pure Air 6+ NOx offgasing, Background VOCs Used primarily to screen for background VOC effects with the NOx offgasing and chamber radical source parameter set at values that fit the other types of characterization experiments. 32 Table 3. Summary of initial experiments carried out in the chamber.

Average  ( O3 NO) Model Fits [ c] Run Type [ a] Runs [ b] NOx ( ppb) CO ( ppm) VOC ( ppb except as noted) Bias Error Pure Air 6 0 0 0 See note [ d]

Other Characterization 32 0 202 0 168 0 490  3% 28%

HCHO   NOx 2 8  23 35 50  23% 23%

HCHO  CO  NOx 2 16  21 14 76 39 49  10% 10%

Ethene   NOx 2 10  25 617 650  15% 15%

Propene   NOx 2 5  24 42 52 16% 16%

Toluene   NOx 3 5  24 61 152 11% 11%

m Xylene  NOx ( arc light) 1 5 18 6% 6%

m Xylene  NOx ( blacklight) 18 17 100 25 215 [ e]

Toluene  CO  NOx 5 4  27 24 50 55 165  16% 17%

m Xylene   CO  NOx 1 6  6 47 18  21% 21%

Surrogate  NOx 61 [ f] 2  315 0.2  4.2 [ g]  10% 13%

[ a] Arc light used unless indicated otherwise [ b] Each reactor irradiation is counted as a separate run, so two runs are done at once.

[ c] Error and bias for model predictions of  ([ O3][ NO]) using the SAPRC 99 mechanism. Bias is ( calculated  experimental) / calculated. Error is the absolute value of the bias.

[ d] The average 6 hour O3 yields for the pure air runs with blacklights and standard conditions are 4 ± 2 ppb experimental and 6 ± 2 ppb calculated. [ e] Not used for gas phase mechanism evaluation. See discussion of SOA yield experiments.

[ f] Includes experiments carried out for subsequent projects [ g] ppmC 33 20 ft. 20 ft. 20 ft. This volume kept clear to maintain light uniformity Temperature controlled room flushed with purified air and with reflective material on all inner surfaces Dual Teflon Reactors Two air Handlers are located in the corners on each side of the light ( not shown).

Gas sample lines to laboratory below Access Door 200 KW Arc Light 2 Banks of Blacklights SEMS ( PM) Instrument Floor Frame Movable top frame allows reactors to collapse under pressure control Mixing System Under floor of reactors Figure 1. Schematic of the environmental chamber reactors and enclosure.

0.0 0.2 0.4 0.6 0.8 0.300 0.350 0.400 0.450 0.500 0.550 0.600 Wavelength ( microns) UCR EPA Blacklights Solar Z= 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.290 0.300 0.310 0.320 Relative Intensity ( Normalized to give same NO2 photolysis rate)

Figure 2. Spectrum of the argon arc light source used in the chamber. Blacklight and representative solar spectra, with relative intensities normalized to give the same NO2 photolysis rate. 34 0 1 2 3 4 5 6 7 50 75 100 125 150 175 EPA Run Number NOx or Radical Input ( ppt/ min)

Radical Input ( Side A)

Radical input ( Side B)

NOx Input ( Side A)

NOx Input ( Side B)

Used in Model ( Side A)

Used in Model ( Side B)

Figure 3. Plots of NOx or radical input rates necessary for model simulations to predict the experimental data against experimental run number ( i. e., against the order the experiment was carried out). 35 1 10 100 1000 290 300 310 320 Average Temperature ( K) HONO Offgasing Paramenter, RN ( ppt)

Previous UCR Indoor Previous UCR Outdoor Previous UCR Default Model UNC Outdoor Model TVA Indoor ( NOx offgasing)

UCR EPA ( first series)

UCR EPA ( later series)

SAPHIR HONO offgasing Figure 4. Plots of the HONO offgasing parameter, RN ( ratios of the HONO offgasing rates the NO2 photolysis rates) derived from modeling characterization runs for various chambers. Data shown are for unhumidified experiments except for the UNC outdoor and TVA chambers.

0 2 4 6 8 10 12 75 125 175 225 275 325 Run No. Particle Decay (/ day)

Side A Side B Avg A Avg B Reactors Changed Figure 5. Plots of particle loss rates against time for experiments from February 2003 through June of 2004 36 Side A Side B Maximum PM Number 0.0 0.5 1.0 1.5 2.0 150 200 250 300 350 Run Number 5 Hour PM Volume ( ug/ m3) Pure Air Propene  NOx First Run in New Reactor 150 200 250 300 350 Run Number CO  Air, CO  NOx Blacklight 0 5000 10000 15000 20000 150 200 250 300 350 Run Number Maximum PM Number 150 200 250 300 350 Run Number PM Volume at 5 Hours of Irradiation Figure 6. Plots of 5 Hour PM volume and maximum PM number data in PM background characterization experiments in the reactors installed before run 169. 37 All Characterization HCHO  NOx HCHO  CO  NOx Ethene  NOx Propene  NOx Toluene  NOx Toluene  CO  NOx m Xylene  NOx m Xylene  CO  NOx Surrogate  NOx  75%  50%  25% 0% 25% 50% 75%

( Calculated  Experimental) / Experimental Single Run Average Figure 7. Fits of experimental O3 formed and NO oxidized,  ([ O3][ NO]), measurements to SAPRC 99 model calculations for the initial chamber and mechanism evaluation experiments. 38  50%  40%  30%  20%  10% 0% 10% 20% 30% 40% 50%

1 10 100 1000 ROG / NOx ( ppmC / ppmN) ( Experimental  Calculated) / Experimental  ([ O3][ NO])

( Experimental  Calculated) / Experimental  ([ O3][ NO])

Figure 8. Plots of the tendency of the SAPRC 99 mechanism for underpredicting ozone formed and NO oxidized,  ([ O3][ NO]), against the initial ROG/ NOx ratio in the surrogate  NOx experiments. Error bars show the effect of varying the HONO offgasing chamber effects parameter within its uncertainty. 39 Concentration ( ppm) vs Time ( minutes) O3 0.00 0.01 0.02 0.03 0.04 0 120 240 360 NO 0.000 0.001 0.002 0 120 240 360 NO2 0.0000 0.0005 0.0010 0.0015 0 120 240 360 m Xylene 0.000 0.002 0.004 0.006 0 120 240 360 PAN 0.0000 0.0002 0.0004 0.0006 0 120 240 360 NOy  HNO3 0.000 0.001 0.002 0.003 0.004 0 120 240 360 Experimental Standard Model No HONO Offgasing Maximum HONO Offgasing Figure 9. Concentration time plots of selected compounds in the lowest NOx ambient ROG  NOx surrogate experiment in the initial evaluation experiments ( NOx   1 ppb, ROG   300 ppbC. 40 0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 0 50 100 150 200 250 300 Mo( µ g/ m3) Yield Empirical fit through UCR data Caltech data for dry m xylene experiments UCR data for dry m xylene Figure 10. Comparison of yield data obtained for m xylene/ NOx system with blacklight irradiation. Solid squares represent data obtained in this reactor ( UCR); open diamonds are for dry experiments conducted in the Caltech reactor ( Cocker et al., 2001b); the solid line represents the best fit two product model for the current UCR data set.