A31E-01 INVITED 

Chemistry of Volatile Organic Compounds and Organic Aerosol in the Outflow from Mexico City

* de Gouw, J A (Joost.deGouw@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway CSD7, Boulder, CO 80305, United States * de Gouw, J A (Joost.deGouw@noaa.gov), CIRES, University of Colorado, Campus Box 216, Boulder, CO 80309, United States Welsh-Bon, D (Daniel.WelshBon@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway CSD7, Boulder, CO 80305, United States Welsh-Bon, D (Daniel.WelshBon@noaa.gov), CIRES, University of Colorado, Campus Box 216, Boulder, CO 80309, United States Welsh-Bon, D (Daniel.WelshBon@noaa.gov), Department of Chemistry & Biochemistry, University of Colorado, Campus Box 215, Boulder, CO 80309, United States Warneke, C (Carsten.Warneke@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway CSD7, Boulder, CO 80305, United States Warneke, C (Carsten.Warneke@noaa.gov), CIRES, University of Colorado, Campus Box 216, Boulder, CO 80309, United States Kuster, W C (William.C.Kuster@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway CSD7, Boulder, CO 80305, United States Huey, L G (greg.huey@eas.gatech.edu), Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States Sullivan, A P (sullivan@atmos.colostate.edu), Colorado State University, 200 West Lake Street, Fort Collins, CO 80523, United States Weber, R J (rweber@eas.gatech.edu), Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States Stone, E A (eastone@wisc.edu), University of Wisconsin, 660 North Park Street, Madison, WI 53706, United States Schauer, J J (jjschauer@wisc.edu), University of Wisconsin, 660 North Park Street, Madison, WI 53706, United States

The MILAGRO study in March of 2006 was aimed at studying air pollution in the Mexico City basin, and at the transport and atmospheric impact of the primary and secondary pollutants on the regional and global atmosphere. Measurements of volatile organic compounds (VOCs) and of (water-soluble) organic carbon at a sub-urban site to the north of Mexico City (T1), are used to characterize the emissions and chemical removal of VOCs and the resulting formation of secondary products. The emission ratios of most VOCs, relative to carbon monoxide (CO), are about a factor of 2 higher in Mexico City than in the U.S. On the other hand, formation of oxygenated VOCs and secondary organic aerosol is comparable between Mexico City and the U.S. The contribution of biomass burning emissions is investigated using measurements of acetonitrile, and the results are compared to a chemical mass balance approach based on measurements of molecular markers such as levoglucosan.

A31E-02 

Evolution of Diesel Exhaust Aerosol in an Urban Environment

* Kroll, J H (kroll@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Smith, J D (jdsmith@lbl.gov), Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, United States Wilson, K R (KRWilson@lbl.gov), Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, United States Canagaratna, M (mrcana@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Herndon, S C (herndon@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Onasch, T B (onasch@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Wood, E C (ezrawood@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Worsnop, D R (worsnop@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Ahmed, M (mahmed@lbl.gov), Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, United States Leone, S R (srleone@lbl.gov), Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, United States

We present laboratory and field measurements of the composition of the largely unoxidized fraction of organic aerosol found in urban areas. Aerosol evolution from the oxidation of the low-volatility fraction of diesel exhaust was studied by reacting emissions from a modern diesel engine with OH in a flow reactor. The exhaust was first passed through a charcoal denuder, which removed all volatile components and left only semivolatile and intermediate-volatility organic compounds (SVOC's and IVOC's) available for reaction. Oxidation leads to a substantial (40%) increase in aerosol mass and volume, indicating the formation of secondary organic aerosol (SOA) from these compounds. Measurement of the aerosol composition using an Aerodyne aerosol mass spectrometer (AMS) indicates a very low level of oxidation, in contrast with most other laboratory-generated SOA. This is likely because large, relatively low-volatility hydrocarbons require only a small degree of oxidation (addition of 1-2 oxygen atoms) to be of sufficiently low vapor pressure to partition efficiently into the aerosol phase. An aerosol component with a very similar mass spectrum is derived from factor analysis of aerosol mass spectra taken in and around Mexico City as part of the MILAGRO 2006 campaign. This component has a mass spectrum that is distinct from that corresponding to primary diesel emissions ("hydrocarbon-like organic aerosol"). The similarities and relationships between this aerosol component and the aerosol generated from the laboratory oxidation of diesel exhaust will be discussed.

A31E-03 

Volatile Organic Compounds (VOCs) measured aboard the Ronald H. Brown during TexAQS 2006 and their OH reactivity.

* Gilman, J B (jessica.gilman@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States * Gilman, J B (jessica.gilman@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States Kuster, W C (william.c.kuster@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Goldan, P D (paul.d.goldan@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Goldan, P D (paul.d.goldan@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States Warneke, C (carsten.warneke@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Warneke, C (carsten.warneke@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States deGouw, J A (joost.degouw@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States deGouw, J A (joost.degouw@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States Lerner, B M (brian.lerner@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Lerner, B M (brian.lerner@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States Williams, E J (eric.j.williams@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Williams, E J (eric.j.williams@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States Brown, S S (steven.s.brown@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Brown, S S (steven.s.brown@noaa.gov), CIRES, UCB 215, Boulder, CO 80304, United States Hostoff, H (hostoff@ucalgary.ca), University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada Herndon, S (herndon@aerodyne.com), Aerodyne, Inc., 45 Manning Road, Billerica, MA 01821, United States Zahniser, M (mz@aerodyne.com), Aerodyne, Inc., 45 Manning Road, Billerica, MA 01821, United States

Volatile Organic Compounds (VOCs) are a critical component in the photochemical production of ozone. Along the coast of Texas there is an immense variety of industrial, urban, and biogenic sources of VOCs. Formaldehyde measurements from a Quantum Cascade Laser-Tunable Infrared Laser Differential Absorption Spectrometer (QCL-TILDAS) and VOC measurements from a Gas Chromatograph-Mass Spectrometer (GC-MS) were used in an effort to characterize the VOC sources and identify the key reactive species that contribute the most to potential ozone formation in the Houston/Galveston area. Ethane and propane had the highest median mixing ratios at 4.7 and 3.0 ppbv, respectively, while n-butane had the highest maximum mixing ratio of 467.7 ppbv in a single sample. Ethene, propene, isoprene, formaldehyde, and acetaldehyde had the highest median calculated OH reactivities ranging from 0.13 to 0.34 s-1, while vinyl acetate had the highest maximum contribution to OH reactivity at 91.7 s-1 in a single sample. The data from the GC-MS shows that the total OH reactivity was dominated by VOCs when compared to CO, CH4, and NO2 throughout the Galveston/Houston area and had values ranging between 1-200 s-1. Diurnal profiles of the OH reactivity show the buildup of reactive VOCs in the early morning hours just before sunrise and their subsequent photochemical processing.

A31E-04 

Photochemically produced secondary organic aerosol and ozone in the Houston Ship Channel during TexAQS-GoMACCS 2006

* Herndon, S (herndon@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Onasch, T (onasch@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Allan, J (james.allan@manchester.ac.uk), School of Earth, Atmospheric and Environmental Science, The University of Manchester, Sackville Street Building PO Box 88, Manchester, UK M60 1QD, United Kingdom Wood, E (ezrawood@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Zahniser, M (mz@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Canagaratna, M (mrcana@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States Lerner, B (Brian.Lerner@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Welshbon, D (daniel.welshbon@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Gillman, J (Jessica.Gilman@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Sommariva, R (Roberto.Sommariva@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Roberts, J (Jim.Roberts@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Aikin, K (Kenneth.C.Aikin@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Brewer, A (alan.brewer@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Tucker, S (Sara.Tucker@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Bates, T (Tim.Bates@noaa.gov), NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, United States Quinn, P (Patricia.Quinn@noaa.gov), NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, United States Kuster, B (Bill.Kuster@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Williams, E (Eric.Williams@noaa.gov), NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Kroll, J (kroll@aerodyne.com), Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821, United States

The organic particulate matter measured using the aerosol mass spectrometer has been deconvolved into multiple organic components using positive matrix factorization techniques including hydrocarbon-like organic aerosol (HOA) and oxygenated organic aerosol (OOA). The correlation between OOA and Ox (Ox = NO2 + O3) will be explored. The ratio of SOA production to ozone production should depend on the VOC composition since they are both photochemical processes. VOC emissions in the Houston Ship Channel and Galveston Bay area are diverse: urban, marine diesel, petrochemical, industrial. This analysis will challenge the understanding of SOA production in the context of urban emissions. Organic aerosol can be further oxidized in the atmosphere. One product of that oxidation which may represent a particle to gas process is formic acid. The processes contributing to gas phase production will be evaluated and upper limits for the potential heterogenous production will be presented.

A31E-05 

Reactive nitrogen chemistry in Mexico City outflow â€" a unique case

* Flocke, F (ffl@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Weinheimer, A (wein@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Hodzic, A (alma@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Emmons, L (emmons@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States McKenna, D (danny@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Tie, X (xxtie@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Madronich, S (sasha@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Zheng, W (wengang@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Montzka, D (montzka@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Knapp, D (knapp@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Campos, T (campos@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Apel, E (apel@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Hills, A (hills@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Mauldin, L (mauldin@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Cantrell, C (cantrell@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Anderson, R (rsa@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Kosciuch, E), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Jimenez, J (jose.jimenez@colorado.edu), CIRES - University of Colorado, 216 UCB, Boulder, CO 80309, United States DeCarlo, P (peter.decarlo@colorado.edu), CIRES - University of Colorado, 216 UCB, Boulder, CO 80309, United States Dunlea, E (edward.dunlea@colorado.edu), CIRES - University of Colorado, 216 UCB, Boulder, CO 80309, United States Aiken, A (allison.aiken@colorado.edu), CIRES - University of Colorado, 216 UCB, Boulder, CO 80309, United States Atlas, E (eatlas@rsmas.miami.edu), RSMAS - University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, United States Blake, D (dblake@uci.edu), University of California, Irvine, Dept. of Chemistry 570 Rowland Hall, Irvine, CA 92697, United States Meinardi, S (smeinard@uci.edu), University of California, Irvine, Dept. of Chemistry 570 Rowland Hall, Irvine, CA 92697, United States Baker, A (abaker@uci.edu), University of California, Irvine, Dept. of Chemistry 570 Rowland Hall, Irvine, CA 92697, United States Beyersdorf, A (abeyersdorf@uci.edu), University of California, Irvine, Dept. of Chemistry 570 Rowland Hall, Irvine, CA 92697, United States Karl, T (tomkarl@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Clarke, T (tclarke@soest.hawaii.edu), University of Hawaii, Department of Oceanography 1000 Pope Road, Honolulu, HI 96822, United States Shinozuka, Y (yohei@hawaii.edu), University of Hawaii, Department of Oceanography 1000 Pope Road, Honolulu, HI 96822, United States McNaughton, C (cameronm@soest.hawaii.edu), University of Hawaii, Department of Oceanography 1000 Pope Road, Honolulu, HI 96822, United States Zhou, J (jczhou@hawaii.edu), University of Hawaii, Department of Oceanography 1000 Pope Road, Honolulu, HI 96822, United States Springston, S (srs@bnl.gov), Brookhaven National Laboratory, Atmospheric Sciences Division Building 815E 75 Rutherford Drive, Upton, NY 11973, United States Skamarock, W (skamaroc@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States Fast, J (Jerome.Fast@pnl.gov), Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99352, United States Voss, P (pvoss@email.smith.edu), Smith College, 51 College Lane, Northampton, MA 01063, United States Zaveri, R (Rahul.Zaveri@pnl.gov), Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99352, United States Wennberg, P (wennberg@gps.caltech.edu), CalTech, Div. of Geological and Planetary Sciences MS 150-21, Pasadena, CA 91125, United States Crounse, J (crounjd@caltech.edu), CalTech, Div. of Geological and Planetary Sciences MS 150-21, Pasadena, CA 91125, United States McCabe, D (dmcc@gps.caltech.edu), CalTech, Div. of Geological and Planetary Sciences MS 150-21, Pasadena, CA 91125, United States

The chemistry and fate of reactive nitrogen emitted from Mexico City is examined. Measurements of NOx, NOy, PANs, alkyl nitrates, HNO₃, and particulate nitrate were made on board the NCAR/NSF C-130 aircraft during the 2006 MILAGRO campaign. Near- and far-field outflow from the Mexico City metropolitan area was probed by the C-130 ranging from city overflights to a distance of 1000 km from the city. Reactive nitrogen and CO measurements made on board the DOE G-1 aircraft are also used. In addition, Mexico City outflow was successfully tagged by two radio controlled CMET Balloons and the same air was measured on two consecutive days during the March 18/19 outflow event. The reactive nitrogen data is examined with regard to NOy partitioning, ozone formation efficiency, and the ultimate fate of NOy, as a function of time and distance from the city. The NOx sequestration chemistry is examined using the WRF-Chem model. Because of the unique conditions in Mexico City with regard to altitude and climate as well as the high particle loading in the area the chemistry in the Mexico City outflow is very different compared to other mega-cities such as New York City. These differences and the resulting impacts on the region around the city will be discussed.

A31E-06 

NOy partitioning and the role of alkyl nitrates in Tecamac, Mexico

* Farmer, D K (delphine.farmer@colorado.edu), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, United States * Farmer, D K (delphine.farmer@colorado.edu), Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, United States Perring, A E (aperring@berkeley.edu), Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, United States Wooldridge, P J (pjwool@berkeley.edu), Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, United States Cohen, R C (cohen@cchem.berkeley.edu), Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, United States Cohen, R C (cohen@cchem.berkeley.edu), Department of Earth and Planetary Science, University of California at Berkeley, Berkeley, CA 94720, United States Cohen, R C (cohen@cchem.berkeley.edu), Environmental Technologies Division, Lawrence Berkeley National Labs, Berkeley, CA 94720, United States Huey, L G (greg.huey@eas.gatech.edu), School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States Sjostedt, S (sjosted67@yahoo.com), School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States Tanner, D (tanner@eas.gatech.edu), School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States Vargas, O), School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States deGuow, J), Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO 80305, United States Warneke, C (Carsten.Warneke@noaa.gov), Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO 80305, United States Kuster, W C (William.C.Kuster@noaa.gov), Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO 80305, United States Blake, D (drblake@uci.edu), Department of Earth System Science, University of California at Irvine, Irvine, CA 92697, United States Baker, A (akyoung@uci.edu), Department of Earth System Science, University of California at Irvine, Irvine, CA 92697, United States

The reactive nitrogen oxide (NOy) budget observed at the T1 site in Tecamac, MX during the MILAGRO campaign in March 2006 allows us to probe the role of alkyl nitrates (ANs) and peroxy nitrates (PNs) in a polluted megacity region. Comparing data from the Mexico City region to previous field sites at Granite Bay, California and Houston, Texas demonstrate that each site has a characteristic nitric acid and alkyl nitrate production efficiency depending on the balance of NOx and VOCs. This balance in turn affects the ozone production efficiency. Unlike Granite Bay and Houston, little isoprene was observed at Tecamac: the result is an alkyl nitrate (AN) population with a higher observed branching ratio (~7 %). The observed branching ratio is consistent with predictions based on the VOC distribution and predicted OH reactivity at the site. These predictions suggest that aromatics and multifunctional ANs such as hydroxyalkyl nitrates make up a large fraction of ANs in the Mexico City plume, and have implications to ozone production and air quality in the region.

A31E-07 

Observations of nitric acid removal that strongly affects the relationship between ozone and NOx oxidation products

* Neuman, J (andy.neuman@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Coloado, Boulder, CO 80309, United States * Neuman, J (andy.neuman@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Nowak, J B (john.nowak@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Coloado, Boulder, CO 80309, United States Nowak, J B (john.nowak@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Zheng, W (wengang@ucar.edu), Cooperative Institute for Research in Environmental Sciences, University of Coloado, Boulder, CO 80309, United States Zheng, W (wengang@ucar.edu), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Zheng, W (wengang@ucar.edu), Atmospheric Chemistry Division, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80305-3000, United States Flocke, F (ffl@ucar.edu), Atmospheric Chemistry Division, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80305-3000, United States Ryerson, T (thomas.b.ryerson@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Trainer, M (michael.k.trainer@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Holloway, J (john.s.holloway@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Coloado, Boulder, CO 80309, United States Holloway, J (john.s.holloway@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Parrish, D (david.d.parrish@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States Fehsenfeld, F (fred.c.fehsenfeld@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Coloado, Boulder, CO 80309, United States Fehsenfeld, F (fred.c.fehsenfeld@noaa.gov), NOAA Earth System Research Lab, 325 Broadway, R/CSD 7, Boulder, CO 80305, United States

Over the past 20 years, the relationship between ozone formation and NOx precursors has been examined in order to understand the factors that control ozone pollution. Understanding the fate of NOx and its oxidation products is necessary to accurately determine the dependence of ozone upon NOx. Measurements of ozone, NOx, and NOx oxidation products were obtained from the NOAA WP-3 aircraft during the 2006 Texas Air Quality Study under a variety of meteorological conditions in plumes downwind from Houston, Texas. Over 50 crosswind transects of coalesced plumes from the Houston urban and industrial areas were examined. Nitric acid, which is one of the primary NOx oxidation products, can be removed rapidly from the atmosphere by deposition. This deposition affects reactive nitrogen partitioning and causes an increase in the slope of the correlation between ozone and the products of NOx oxidation (often interpreted as ozone production efficiency). During this study, nitric acid loss increased when wind speeds were high, causing the ozone to NOy-NOx correlation slopes to increase dramatically. Accounting for this loss is necessary to use correlation slopes of ozone versus NOy-NOx to represent an ozone production efficiency that describes the NOx-VOC chemistry.

A31E-08 

Impact of Clouds and Aerosols on Photochemistry During the TexAQS II Radical and Aerosol Measurement Project

* Flynn, J H (jhflynn@uh.edu), University of Houston, Department of Geosciences, 4800 Calhoun Road Room 312 SR-1, Houston, TX 77204, United States Lefer, B L (blefer@uh.edu), University of Houston, Department of Geosciences, 4800 Calhoun Road Room 312 SR-1, Houston, TX 77204, United States Rappenglueck, B (brappenglueck@uh.edu), University of Houston, Department of Geosciences, 4800 Calhoun Road Room 312 SR-1, Houston, TX 77204, United States Olson, J R (jennifer.r.olson@nasa.gov), NASA Langley Research Center, Chem & Dynamics Branch, Mail Stop 401B, Hampton, VA 23681, United States Chen, G (gao.chen@nasa.gov), NASA Langley Research Center, Chem & Dynamics Branch, Mail Stop 401B, Hampton, VA 23681, United States

Photochemistry is responsible for the production of tropospheric ozone, the primary component of smog. In 2006, Houston, Texas experienced 20 days with a 1-hour ozone average in excess of 125 ppbv, and 36 days with an 8-hour average over 85 ppbv. Two models were used to assess the impact of clouds and aerosols on the photochemical production and loss of ozone and radicals in a polluted urban environment. The NASA Langley Research Center (LaRC) 0-D photochemical box model was used to assess the changes in the photochemical budgets due to varying cloud and aerosol conditions. The NCAR Tropospheric Ultraviolet and Visible (TUV) radiative transfer model was used to calculate photolysis frequencies for clear sky conditions with a variety of aerosol profiles. These tools were used to analyze the data set collected during the Texas Air Quality Study II Radical and Aerosol Measurement Project (TRAMP) with respect to ozone and radical budgets. Measurements of trace gasses, aerosols, meteorological parameters, and radiation were collected between mid-August and early October 2006 at the University of Houston. The photochemical model was run using various photolysis rates that reflect a range of atmospheric conditions impacting the actinic flux. Rates from real-time actinic flux measurements include the impact of both the clouds and aerosols that are present. Photolysis rates for clear-sky (cloud-free) conditions, both with and without aerosol profiles were calculated using the TUV radiative transfer model. A comparison of the photochemical ozone and radical budgets resulting from these different rates indicate those sensitivities to the presence of aerosols and clouds. Approximately seven of the 50 days during the campaign were cloud-free and were compared to LaRC-TUV results to show the effects of aerosols. The remaining days show the effects of both aerosols and cloud conditions that varied from partly cloudy to heavy overcast conditions. A cloud camera was used to categorize the sky condition based on coverage and type of clouds. Results from this work, particularly the results of the aerosol impacts, can be utilized in photochemical models to improve the closure between ozone measurements and both forecasts and hindcasts.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.