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""""""5""""""2""!!%E !"00000=..****1!0!0!0!0!1!1!1!1!0!012"0!0!1!&!2!22....2"****2"2"2"2"2"2"2"""1%2"*****2"'2"2"2"2"=2...&$&&**2"2"2"2"2"A22"*+Nd"""""";"!!!"; "ECC""))3C!C!0!(88&&E!?E"^@ViVVV@V@HHHrVdVHVyV~rEP~rr~~{3{V@VV+VVVSVVVVVV}VgH~~~~SCSCSCSCs~~~~VEVEVEVEdP~~~~~rkrr~~~iiiiiiiiiiiiiNZd@uVrGPX}}}X.SrrVV}}}Vr}X"S^ +(  /%""%%%%.%%%"%%1%%(%  3 $$$$$.""%$$$$%%%%$$%%$$%%%%""""%%%%%%%%%%%%%%%.%"""%%%%%1%% Nd ,, 322&22$**3/3"^@dVVV@V@HVVdVHVVrrVHHHddHrrdZ9ZV@VV+VVVSVVVVVV}VH}}}}}oooooaEaEaEaE}}}}o}}o}}rrrrrrrrdEddVdVHVVXHddddaddVVrdaNZd@dDMS}}}SHSVV}}}V}S2%+kp lFZ>z"S^#++GC+0++++++++++000&O>99>40>>!>4L>>0>904>>Q>>4(+&+&+&+++C++++!++>++&)).V*+<%<%<%<%<%L99%4%4%4%4%>*<*<*<*<*>*>*>*>*<*<%>>+<*<*>*0*>*>&>&9&9&9&9&>+4&4&4&4&>+>+>+>+>+>+>+++=.!>+44444>+1>+>+>+>+L>9990!- 0!0!44>+>+>+>+>+Q>>+4&6%Nd'+&+++++J+***+J&&+VSS++33?S*S*<*1EE00V&*OV 7iC3,ƒXi\  P6XP RdM,\  P6P RdM,c4  p 7nC3,4Xn4  pX @{N<,M{\  P6P @N<,4  p g'J/$, J\  P6P M^I,baR\  P6RP  M^I,tR4  pRZ J^I,%MQR*f9 xr RX  L^I,<R9 xOR g'N/$,ǺN4  pZ i%J/$,%7J*f9 xr X t,X5),WX4  p 7nC3,4Xn4  pX W!?(,,h?\  P6hP "DS@,\  P6P"|4xC;,XXx*0 x]7X DS@,A4  p! #DSH,m\  PAPZ BS@,%*f9 xr X$ $m)O2',alO\  P6P 7gC9,mXg\  PAXPZ 5hC3,%Xh*f9 xr XX t,T5),AzT\  P6P 2`=/,"&`\  P6&P  2e=/,4[&e4  p& k(Q1&,הQ4  p2e=/,4[&e4  p& k(M1&,M\  P6P2`=/,"&`\  P6&PZ 0_=/,% &_*f9 xr &X P:%,J:\  P6JPDS@,A4  p!DS@,\  P6P" 0#,#\  P6P DS@,<tP9 xO %<,,,\  P6P&& &$ , \  P6Pvv s  V #u\  PP# The 1997 Southern California Ozone Study-NARSTO:  sM Aerosol Program and Radiation Study  aA  d #[\  PMP# 98-A633  X #XN\  PƒXP# Nehzat Motallebi, James Pederson, Bart E. Croes, Tony VanCuren California Air Resources Board, P.O. Box 2815, Sacramento, CA 95812-2815  XI  Susanne V. Hering Aerosol Dynamics, Incorporated, 2329 Fourth Street, Berkeley, CA 94710  X  Kimberly A. Prather University of California at Riverside, Department of Chemistry, 1148A Pierce Hall, Riverside, CA 92521-0403  Xf  Mary Ann Allan EPRI, Environment Division, P.O. Box 10412, Palo Alto, CA 94303-0813  a #[\  P MP# ABSTRACT  Xn #XN\  P ƒXP#The 1997 Southern California Ozone Study-North American Research Strategy for Tropospheric Ozone (SCOS97-NARSTO, http://www.arb.ca.gov/scos/scos.htm) was an extensive monitoring study conducted from June16 through October15, 1997. The study goals were to provide aerometric and emission databases to support photochemical air quality simulation model applications for representing urban- and regional-scale ozone episodes in southern California. In order to better understand interactions among ozone, particles, and ultraviolet radiation in Californias South Coast Air Basin (SoCAB), the SCOS97-NARSTO Aerosol Program and Radiation Study was implemented from August16 to September29, 1997. Six studies were coordinated with each other and with the ozone study. Fourteen groups of researchers deployed advanced continuous and filter-based aerosol measurement equipment at surface sites, an array of solar radiometers, and an aircraft instrumented with advanced aerosol analyzers. Preliminary results from a real-time single-particle analyzer for August 22, 1997 suggest a link between high ozone and high fine organic aerosol levels. Further data reporting and interpretation of measurements will come from the various participants over the next year, culminating in a SCOS97-NARSTO Data Analysis Conference during the summer of 1999. These studies should help us understand the origins and processing of primary (directly emitted) particles and the chemical processes that convert gases into secondary particles. From this we should be able to determine how strongly ozone control programs will affect aerosol concentrations in the SoCAB and quantify the effects of aerosols on ozone formation, especially with regard to the new national 24-hour-average PM2.5 and 8-hour-average ozone standards.  a% #[\  P MP# INTRODUCTION  XF' #XN\  P ƒXP#The 1997 Southern California Ozone Study, conducted under the Charter of the North American Research Strategy for Tropospheric Ozone (SCOS97-NARSTO), consisted of extensive monitoring of emission activity, meteorology, and air quality in southern)0*0*0* California from June16 through October15, 1997. It is being followed by comprehensive photochemical air quality simulation modeling and data analysis. The results will be used to improve the understanding of ozone episodes in southern California for use in developing  X air quality management plans. The SCOS97-NARSTO field study plan1 and several papers  X in this conference2-7 provide background information and a conceptual model for the ozone episodes and transport scenarios of interest, and summarize the data collection and quality assurance activities, as well as plans for data management and emission inventory development. Not only do ozone episodes need to be understood, the causes of high levels of aerosols also require study because of the impact of particulate matter on human health. In the South Coast Air Basin (SoCAB) during the years 1990 through 1996, 59 to 74% of the days each year with 24-hour-average sampling violated the California ambient air quality  XP standard for PM10 (50%g/m3) and 1 to 8% exceeded the 24-hour-average national standard  X9 (150%g/m3). During the period 1994 to 1996, the SoCAB had the highest 24-hour-average  X" PM2.5 concentration (115%g/m3) observed in California,8 substantially exceeding the new  X  national standard (65%g/m3). Since monitoring is the basis for assessing whether or not the public health is protected, the new particulate matter regulations also motivate a comparison of existing routine and research measurement methods for PM2.5 with the new Federal reference method (FRM) in order to quantify and understand the sources of any differences in results. Analysis of data from 1986 and 1987 PM2.5 measurement programs in the  X SoCAB by Hering and Cass9 show that the mean basin-wide loss of ammonium nitrate from  X sampling with Teflon filters varies from 4 to 7g/m3, or about 25 to 50% of the new  Xj annual-average national standard (15%g/m3). In addition to their direct impact on human health, aerosols influence the rate of formation  X of ozone by scattering and absorbing ultraviolet (uv) radiation. Dickerson and coworkers10 showed that uv-absorbing aerosols can inhibit, and uv-scattering aerosols can accelerate, photochemical reactions and ozone production, in some cases resulting in decreased photolytic rates at the surface but increased rates a few hundred meters aloft. Since aerosol-uv radiation interactions are not represented in most current photochemical models, model applications for ozone and particulate matter may not be realistic assessments of the effects of emission controls. Interactions among ozone, aerosols, and uv radiation were expected to be most significant during late summer and early fall in the SoCAB, when some of the highest ozone and PM2.5 levels in the U.S. have been recorded. In order to take advantage of the enhanced data collection during the SCOS97-NARSTO, the SCOS97-NARSTO Aerosol Program and Radiation Study was implemented in the form of six studies coordinated with each other and with the ozone study. This paper summarizes the goals and objectives of the SCOS97-NARSTO Aerosol Program and Radiation Study, the measurement activities, and plans for data analysis and modeling.  a% #[\  P MP# GOALS AND OBJECTIVES  X}& #XN\  P ƒXP#The goals of the SCOS97-NARSTO Aerosol Program and Radiation Study were to develop a three-dimensional picture of the generation and evolution of typical late summer and early fall aerosols in the SoCAB, and to provide observations to support modeling of the emissions, meteorological transport and dispersion, and photochemical reactions forming8)0*0*0* ozone, PM2.5, and PM10. The specific objectives were to understand: XHow aerosol size and composition change throughout the SoCAB due to deposition, transport, dispersion, and interactions with gas and particle emission sources.(# XThe relative contributions of various sources, especially gasoline-fueled vehicles and heavy-duty diesel-fueled trucks, to the primary and secondary aerosol burdens.(# XThe formation of secondary aerosols, especially organic and ammonium nitrate aerosols, from gas-phase precursors.(# XThe effects of aerosols on uv radiation and rates of photochemical reactions.(# XThe interactions between control strategies for ozone and particulate matter.(# In addition, the study provided opportunities to evaluate and refine some of the research tools available for aerosol and radiation measurement and interpretive analysis. The specific method development objectives were to: XDevelop calibrations, by particle size and composition, for the aerosol time-of-flight  X mass spectrometer (ATOFMS)11 that can be used to convert the particle counts to concentrations.(# XRelate impactor and filter organic carbon composition to organic carbon fragments measured by the ATOFMS.(# XRefine and extend the library of organic carbon source profiles, especially for gasoline- and diesel-fueled vehicles.(# XImprove aerosol source allocation schemes with the continuous single-particle data available from the ATOFMS.(# XQuantify the composition and amount of labile and volatile fine particulate matter lost from simple filter-based sampling (e.g., the PM2.5 FRM) to characterize as accurately as possible the mass and composition of suspended fine particles at the point of inhalation.(# XEvaluate particulate nitrate stability in samples collected with the PM2.5 FRM.(# XEvaluate the performance of a continuous nitrate analyzer.(# XEvaluate and improve radiative transfer models suitable for calculation of photolytic rates in photochemical models.(# XEvaluate the utility of standard broad-band radiometers, with and without shading, for providing input data for photochemical models.(# XTest a prototype aircraft for measurement of vertical profiles of aerosol precursors and aerosol size and concentration, and for collection of time-averaged aerosol samples aloft for chemical analysis.(# XEvaluate and improve photochemical air quality simulation models for PM2.5.(#  a& #[\  P MP# STUDY SCOPE AND DOMAIN  XQ( #XN\  P ƒXP#Ambient sampling was conducted at sites along two trajectories in the SoCAB (see Figure1). To characterize the generation and evolution of urban aerosols, three sites [Los:)0*0*0* Angeles-North Main, Azusa, and the University of California at Riverside (UCR)] were selected along a trajectory from the emissions-rich central Los Angeles area, through the severely ozone-impacted San Gabriel Valley, and downwind to Riverside, the highest PM2.5 site in the SoCAB and perhaps the U.S. To characterize nitrate dynamics, measurements were made downwind of the most heavily populated portions of the Los Angeles coastal plain in Diamond Bar, immediately downwind of the ammonia-emitting dairy farms of the Chino Basin in Mira Loma, and further downwind in Riverside. To characterize the spatial and temporal variations in radiative quantities and photolytic rates attributable to scattering and absorption by aerosols, measurements were made at the surface in Riverside and above the mixed layer on Mt. Wilson (1725m). The Riverside measurements were made at three sites on the University of California campus [Agricultural Operations (AgOps) monitoring station, College of Engineering-Center for Environmental Research and Technology (CE-CERT) rooftop, and Pierce Hall rooftop] within two miles of each other. The UCR sites were subject to approximately the same airmass, as verified with simultaneous ATOFMS measurements from June29 to July5, 1997. Aircraft sampling over a wider area characterized vertical variations and the spatial extent of aerosol characteristics and irradiance observed along the trajectory. The flight paths are shown in Figures1 and 2. To develop size distributions and composition profiles of fine particles emitted by gasoline- and diesel-fueled vehicles, measurements were made in the Caldecott Tunnel in northern California in November1997.  a #[\  P MP# MEASUREMENT APPROACH  Xj #XN\  P ƒXP#The SCOS97-NARSTO Aerosol Program and Radiation Study consisted of six interconnected studies: a Trajectory Study, a Tunnel Study, a Fine Particle Measurement Study, a PM2.5 Federal Reference Method Nitrate Loss Study, a Radiation Study, and an Aerosol Aircraft Study. Table1 lists all the participating measurement groups and Tables2 through 4 contain a full listing of all the measurements collected. Study dates were generally from August16 to September29, 1997 (see Figure3), with any differences noted below.  a- #[\  P MP# Trajectory Study  X #XN\  P ƒXP#The Trajectory Study collected continuous aerosol size distribution and composition data simultaneously at three sites (see Table2). These data will provide the basis for subsequent work to develop, evaluate, and improve photochemical models to simulate the chemical and physical transformations that occur as particles age and travel in the atmosphere. While many of the measurements were made over the entire 6-week period (August16 to September29, 1997) of the study, the full suite of sampling was conducted over five 48-hour intensive operational periods (IOPs) selected on the basis of meteorological and air quality forecasts. The first set of measurements was made at Los Angeles-North Main, Azusa, and Riverside-Pierce Hall, corresponding to a motor vehicle-dominated west-to-east air trajectory along almost the entire length of the SoCAB. Several novel instruments operated continuously for the two-week duration: ATOFMS single-particle analysis and particle size distribution measurements by optical counters and electrical mobility at all three sites, and continuous aerosol nitrate measurements at Riverside-AgOps. Filter-based sampling was(0*0*0* conducted during the IOPs (August21-22, August26-27) to calibrate the ATOFMS instruments with atmospheric particles and to give further detail on aerosol size and composition. At all three sites, PM2.5 and PM10 composition were measured with 4- to 7-hour-average filter samples for the entire 48-hour period. Micro-orifice impactor samples were collected over one 4-hour period each day at all three sites to determine particle  X composition in six size ranges from 0.056 to 1.8m. The filter and impactor samples are currently being analyzed to determine particle mass and bulk composition (elemental carbon, organic carbon, sulfates, nitrates, ammonium, chloride, and trace elements). In addition, denuder difference samples are undergoing analysis for nitric acid, and stacked filter samples for gas-phase ammonia. Two 48-hour-average PM2.5 filter samples run in parallel collected enough particulate matter for quantification of approximately 50 trace organic species by gas chromatography with mass spectrometry. The second set of measurements (September4-5, September28-29, October31-November1) were conducted at Diamond Bar, Mira Loma, and Riverside-Pierce Hall to focus on nitrate formation along the trajectory. In addition to the continuous and filter-based measurements described above for the first trajectory, continuous gas-phase ammonia and nitric acid measurements were made at Mira Loma to observe their concentration-humidity-temperature-phase dependence with continuous aerosol nitrate measurements.  aw #{\  P6MP# Tunnel Study  X #Xi\  P6ƒXP#A successful data analysis and modeling effort using the database collected during the Trajectory Study depends on the acquisition of detailed emission source profiles for gasoline- and diesel-fueled motor vehicles. The Caldecott Tunnel east of Oakland is uniquely configured with a center bore only open to passenger vehicles and side bores  X where trucks are shunted.12 Thus, the particulate matter concentrations in the center bore are dominated by light-duty gasoline vehicles, and the aerosol burden in the side bores are primarily due to emissions from heavy-duty diesel trucks. During the period November17 through 21, four experiments were conducted with the ATOFMS and the filter-based samplers described above. To aid in data analysis and a carbon balance, the gas-phase  X precursors (i.e., CO, CO2, speciated hydrocarbons, speciated carbonyl compounds, semi-volatile organic species) were sampled. An aerosol lidar was operated outside the tunnel. Data were also collected on fleet characteristics (e.g., count, speed, axles) to help in interpreting the results.  a #{\  P6MP# Fine Particle Measurement Study  X! #Xi\  P6ƒXP#The EPRI-sponsored Fine Particle Measurement Study was conducted at Riverside-AgOps from August16 to September22, 1997 (see Table2 for a list of aerosol monitoring instruments). Both continuous and 24-hour-average samplers were deployed for the study, with duplicate side-by-side samplers installed when possible. Daily sample changes were made at 10:00 a.m. Pacific Daylight Time (PDT). The continuous aerosol nitrate monitor was operated at Riverside-AgOps during the first two weeks, after which time it was moved to the Mira Loma site. Other instruments were operated for the duration of the study. Riverside-AgOps was one of several, approximately five-week-long field sampling campaigns conducted at urban locations throughout the country during 1996 to 1998 as part8)0*0*0* of the EPRI study. These snap shot measurements in Birmingham, Boston, Riverside, Chicago, Dallas, Phoenix, and Bakersfield were designed to give an indication of the geographical and seasonal variability of the PM2.5 mass and composition. Comparison of mass and chemical data from continuous samplers (where loss of labile substances is believed minimal) with data from the more conventional filter-based methods (where losses may occur during or after sampling) will begin to characterize the magnitude of measurement error due to loss of labile substances. Another component of the study is evaluation of sampling methods in the laboratory, with tests aimed at understanding instrument precision, accuracy, and interferences or other limitations. The results of this multi-site/laboratory study will provide direct information on the magnitude of the loss of specific compounds and help guide the direction of future measurement research.  ag #{\  P6MP# PM2.5 Federal Reference Method Nitrate Loss Study  X #Xi\  P6ƒXP#The PM2.5 FRM Nitrate Loss Study was conducted in conjunction with the Trajectory Study. Two FRM samplers were operated side by side at each of the three Trajectory Study sites for the first four experiments. Daily sample changes were made at 1:00a.m. PDT. At each site, one FRM unit collected particles on a Teflon filter and a second on a Teflon-nylon filter pack. Both types of filter packs were analyzed by ion chromatography. These results and those from collocated routine and research PM2.5 samplers will be used to quantify aerosol nitrate losses for the FRM.  a #{\  P6MP# Radiation Study  X #Xi\  P6ƒXP#Building upon the Aerosol Program and using the in-kind services of several universities and agencies, relatively modest additional resources were required to collect a data set sufficient to examine interactions between aerosols and radiative quantities. The relevant radiative quantity for calculation of photolytic rates is the actinic flux (i.e., radiant flux density incident upon a spherical unit area), not the irradiance (i.e., radiant flux density incident upon a unit horizontal area). The spectrally resolved actinic flux, which may vary greatly with altitude, is generally modeled. However, an evaluation of radiative transfer models requires observations of the spectrally resolved total and diffuse irradiance. To provide vertical contrasts, measurements were made in Riverside at CE-CERT and above the polluted mixed layer at Mt. Wilson. At each site, several instruments, described in Table3, provided continuous diurnal characterization of irradiance and aerosols. Three types of spectral radiometers measured total and diffuse spectral irradiance. At each site, for comparison with the spectral measurements, three types of broadband radiometers commonly used in existing networks throughout California were operated in pairs, with and  X without shadow bands. During radiation intensive days at the CE-CERT site, an NO2 actinometer measured the photolytic rate and a LI-COR 1800 spectral radiometer was operated with intermittent manual shading for total and diffuse irradiance. These intensive operational periods were selected for cloud-free conditions, to coincide with ozone or particulate matter episodes, and to take advantage of special aircraft- and ground-based observations of aerosol size and composition. To test the study design and instrument operation, intensive measurements were initially made on June29 to July5, but data recovery at the Mt. Wilson site was incomplete due to logistical and exposure problems. The study began collecting complete data on August21p(0*0*0* when equipment at a new Mt. Wilson site became fully operational. Intensive monitoring on August27-28 and September4-6, 10, and 12 was supported by the highly instrumented Pelican aircraft, described in the following section, which provided vertical profiles of irradiance and aerosol size and concentration. Intensive radiation measurements were also made, but without the support of the Pelican, on August21-23 and October30-November1. During ozone IOPs, an additional aircraft, operated by Sonoma Technology, Inc., measured broadband irradiance (Eppley PSP), humidity, temperature, and  X_ gaseous pollutants, but did not measure aerosols.6  a #{\  P6MP# Aerosol Aircraft Study  X #Xi\  P6ƒXP#For aerosol and radiation measurements aloft (see Table4), the Pelican aircraft was operated by the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS), a consortium of the Office of Naval Research, the Naval Postgraduate School, the California Institute of Technology, and Princeton University. The Pelican is a modified Cessna 337 Skymaster that has been reconfigured as a single engine pusher to allow sampling of unperturbed air from the front of the aircraft. Between August27 and September13, CIRPAS obtained measurements of the concentrations and size distributions of particulate matter and its constituent chemical species.  X Aerosol size distributions in the range from 0.005to 10m diameter were measured by an array of three instruments with approximately 1-minute time resolution. PM2.5 particles were sampled using three parallel sampling trains that provided PM2.5 mass, elemental carbon, organic carbon, sulfates, nitrates, ammonium, chloride, and trace elements. Filter sampling for aerosol composition was performed on a 1-hour sampling duration. For a typical 8-hour flight mission, this allowed for about 7 to 8 series of filter samples per  X< mission. The aircraft was also instrumented to monitor SO2 and broadband solar and uv irradiance. Due to differences in the time resolutions of continuous and filter-based measurements, the Pelican flew two types of paths with different sampling objectives. The primary flight path (Figure1) was designed to observe the three-dimensional evolution of aerosol size and concentration along the same west-to-east path as the first set of Trajectory Study experiments. This flight path consisted of spirals and traverses, and was designed to make use of continuous size and concentration measurements. A secondary flight path (Figure2) was chosen to investigate nitrate dynamics aloft along the Trajectory Study path from Diamond Bar through the ammonia source area in the Chino Valley dairy district and on to the nitrate-rich aerosol found at Riverside. This path included traverses and constant altitude orbits to match the 1-hour sampling time for filter-based sampling that provides information on aerosol composition.  a" #{\  P6MP# DESCRIPTION OF MEASUREMENT PERIOD  XG$ #Xi\  P6ƒXP#A display of the daily maximum 1-hour PM10 [measured with tapered element oscillating microbalance (TEOM)] and ozone concentrations recorded at Riverside-AgOps during continuous and intensive operational periods for the SCOS97-NARSTO Aerosol Program and Radiation Study is given in Figure3. PM10 concentrations could be much higher than  X' shown because the TEOM is heated to between 30 and 50 oC to eliminate humidity effects and a substantial fraction of ambient particles can be semi-volatile material such as aerosol(0*0*0* nitrate and some organic compounds. It is interesting to note that two of the highest PM10 periods during the study occurred after hurricanes off the coast of Mexico brought large amounts of moisture to the SoCAB. A likely explanation is that formation of aerosol nitrate from gas-phase ammonia and nitric acid was favored under the high relative humidity conditions. A statistical summary of the 24-hour-average ozone and PM10, and the average of maximum 1-hour concentrations, between August15 and September30 of 1995 to 1997, is presented in Table5. Ozone and PM10 concentrations were about 20% lower in 1997 than the same time period in 1995. This apparent decline could be due to the introduction of California Phase 2 reformulated gasoline in 1996 or meteorological variability. Increased frequency of positive vorticity advection and mid-atmospheric troughing just west of the Pacific Coast (associated with El Ni9o activity) seemed to contribute to a deeper marine layer and better mixing over the SoCAB during the summer and early fall of 1997. Preliminary analysis of the data taken at Riverside-AgOps during August15 and September30, 1997 show that the PM10 concentrations exhibited an afternoon peak coincident to the ozone peak. Figure4 illustrates this point for August22, 1997 with  XX hourly PM10, ozone, and NOX concentrations. Both PM10 and NOX exhibited a pronounced morning peak concurrent with low ozone concentrations. The real-time, single particle data available from the ATOFMS reveal the sources responsible for the two PM10 peaks. In the morning (Figure5), the majority of particles were soil (rich in Al) and unreacted sea salt. In the afternoon (Figure6), organic and reacted sea salt aerosols were the most abundant particles. The latter result provides evidence for a link between high ozone and high fine organic aerosol levels in the SoCAB. The automated nitrate monitor revealed a double peak in the daily nitrate concentration profiles at Riverside. Nitrate concentrations generally increased in the midmorning hours, decreased around noon, and rose again in the afternoon. The relative magnitude of these two peaks varied from day to day.  a# #{\  P6MP# DATA ANALYSIS AND MODELING PLANS  X #Xi\  P6ƒXP#Each of the six studies has a data analysis or modeling component. Many groups involved in the Aerosol Program, including EPRI, Harvard, BYU, SCAQMD, Caltech, and ADI, will be involved with comparisons among the various aerosol measurement methods. Two of the more intensive efforts are for the Trajectory Study and the Radiation Study. The major objective of the Trajectory Study was to determine the relative contributions of sources such as gasoline engine exhaust, diesel exhaust, woodsmoke, food cooking aerosol, road dust, and secondary organic aerosol to PM2.5 concentrations in the SoCAB. To meet this objective, Professor Glen Cass of the California Institute of Technology will calculate source contributions to the fine organic aerosol concentrations and to overall primary fine particle mass concentrations at the three sampling sites for four of the two-day episodes. Source apportionment of fine organic aerosol and fine aerosol mass concentration will be achieved by applying a chemical mass balance model that relates source contributions to ambient PM2.5 concentrations using molecular markers. The chemical profiles of the emission sources were developed from the Tunnel Study and previous studies. Efforts to evaluate and improve radiative transfer models suitable for simulating the effects)0*0*0* of aerosols on photolytic rates will be led by Professors Robert Harley of the University of California at Berkeley and Nancy Brown of Lawrence Berkeley National Laboratory, and they will incorporate these results into existing photochemical models. In addition, the research instruments at CE-CERT and Mt. Wilson will be used to evaluate collocated broadband irradiance measurements to determine the utility of using existing networks of radiometers to aid in estimating semi-quantitatively the spatial and temporal trends and differences in photolytic rates across the SCOS97-NARSTO modeling domain.  a #{\  P6MP# CONCLUSIONS  X1 #Xi\  P6ƒXP#The SCOS97-NARSTO Aerosol Program and Radiation Study successfully captured extensive aerometric and emission datasets to study the interactions among ozone, particles, and uv radiation. The data will also be used to evaluate the PM2.5 FRM and the next generation of continuous aerosol analyzers. Results from the ATOFMS have already proved useful in investigating the link between high ozone and high fine organic aerosol levels. Further data reporting and interpretation of measurements will come from the various participants over the next year, culminating in a SCOS97-NARSTO Data Analysis Conference during the summer of 1999. These studies should help us understand the origins and processing of primary (directly emitted) particles and the chemical processes that convert gases into secondary particles. From this we should be able to determine how strongly ozone control programs will affect aerosol concentrations in the SoCAB and quantify the effects of aerosols on ozone formation, especially with regard to the new national 24-hour-average PM2.5 and 8-hour-average ozone standards.  aj #{\  P6MP# ACKNOWLEDGEMENTS  X #Xi\  P6ƒXP#The SCOS97-NARSTO Aerosol Program and Radiation Study were a cooperative effort with joint planning and funding by the California Air Resources Board (CARB), the Coordinating Research Council (CRC), EPRI, the National Renewable Energy Laboratory (NREL), and Southern California Edison (SCE) with in-kind support from CARB, the South Coast Air Quality Management District (SCAQMD), and the U.S. Environmental Protection Agency (U.S.EPA). The authors gratefully acknowledge the contributions of John Holmes (CARB), Tim Belian, Kent Hoekman, and Steve Japar (CRC), Pradeep Saxena and Aaron Bator (EPRI), Michelle Bergin, Paul Bergeron, and Brent Bailey (NREL), Rob Farber (SCE), and Larry Cupitt (U.S. EPA) for their logistical and financial support of these projects. Special thanks go to Rudy Eden (SCAQMD) for accommodating numerous space and equipment requests with good grace and humor, Joe Cassmassi (SCAQMD) for knowledgeable daily forecasts of meteorology and air quality, Solomon Teffara (SCAQMD) for support of the PM2.5 FRM Nitrate Loss Study, Susan Inong (UCR Statewide Air Pollution Research Center) for providing logistical support at the AgOps site, and Louis Herse, Robert Del Barrio, Vic Barbarick, Ray Mailhot, and Paul Parecadan (California Department of Transportation) for access and extensive electrical upgrades to the Caldecott Tunnel. The authors also acknowledge Sasha Madronich (National Center for Atmospheric Research), William Barnard (U.S.EPA), Robert Harley (University of California at Berkeley), and William Carter and Dennis Fitz (UCR CE-CERT) for extensive consultation in planning of the Radiation Study, and Robert Cadman and Dr. Robert Jastrow for providing access to the Mt. Wilson Institute. ( 0*0*0*Ԍ a #{\  P6MP# REFERENCES  Xn #Xi\  P6ƒXP#1.XFujita, E.M., et al. (1997) SCOS97-NARSTO Field Study and Quality Assurance Plan (available at http://www.arb.ca.gov/scos/scos.htm), May 12 Working Draft.(# 2.XCassmassi, J. (1998) The 1997 Southern California Ozone Study-NARSTO: IOP Forecast Protocols and Episode Selection, Paper 98-WP75-01, Air & Waste Management Association 91st Annual Meeting, June14-18, San Diego, CA.(#  X 3. XShah, M., et al. (1998) The 1997 Southern California Ozone Study-NARSTO: Preparation of the 1997 Gridded Emission Inventory, Paper 98-WP75-02, Air & Waste Management Association 91st Annual Meeting, June14-18, San Diego, CA.(#  X 4.XBenjamin, M., et al. (1998) Assembling a Biogenic Hydrocarbon Emissions Inventory for the SCOS97-NARSTO Modeling Domain, Paper 98-WP75-03, Air & Waste Management Association 91st Annual Meeting, June14-18, San Diego, CA.(#  X 5.XJackson, B., et al. (1998) The 1997 Southern California Ozone Study-NARSTO: Upper-Air Meteorological Sampling Network, Paper 98-WP75-04, Air & Waste Management Association 91st Annual Meeting, June14-18, San Diego, CA.(# 6.XDolislager, L.J. (1998) The 1997 Southern California Ozone Study-NARSTO: Supplemental Air Quality Sampling Network, Paper 98-WP75-05, Air & Waste Management Association 91st Annual Meeting, June14-18, San Diego, CA.(#  XG 7.XFujita, E.M., et al. (1998) The 1997 Southern California Ozone Study-NARSTO: Quality Assurance and Data Management, Paper 98-WP75-07, Air & Waste Management Association 91st Annual Meeting, June14-18, San Diego, CA.(# 8.XDolislager, L.J., and N. Motallebi (1998) Spatial and temporal variations in ambient  XQ PM2.5 and PM10 in California, submitted to J. Air Waste Manage. Assoc.(# 9.XHering, S., and G. Cass (1998) The magnitude of bias in the measurement of PM2.5 arising from volatilization of particulate nitrate from Teflon filters,  Xr submitted to J. Air Waste Manage. Assoc.(# 10.XDickerson, R.R., S. Kondragunta, G. Stenchikov, K.L. Civerolo, B.G. Doddridge, and B.N. Holben (1997) The impact of aerosols on solar ultraviolet radiation and  X photochemical smog, Science, 278: 827-830.(# 11.XNoble, C.A., and K.A. Prather (1996) Real-time measurement of correlated size and  X composition profiles of individual atmospheric aerosol particles Environ. Sci.  X Technol., 30: 2667-2680.(# 12.XKirchstetter, T.W., B.C. Singer, R.A. Harley, G.R. Kendall, and W. Chan (1996) Impact of oxygenated gasoline use on California light-duty vehicle emissions,  X# Environ. Sci. Technol., 30: 661-670.(#