A43C-1414 

Urban aerosol effects on surface insolation and surface temperature

* Jin, M (mjin@atmos.umd.edu), University of Maryland, College Park, Department of Atmospheric and Oceanic Science, College Park, MD 20752, United States Burian, S J (burian@eng.utah.edu AF:

Urban aerosol particulates may play a fundamental role in urban microclimates and city-generated mesoscale circulations via its effects on energy balance of the surface. Key questions that need to be addressed include: (1) How do these particles affect the amount of solar energy reaching the surface and resulting surface temperature? (2) Is the effect the same in all cities? and (3) How does it vary from city to city? Using NASA AERONET in-situ observations, a radiative transfer model, and a regional climate mode (MM5), we assess aerosol effects on surface insolation and surf ace temperature for dense urban-polluted regions. Two big cities, one in a developing country (Beijing, P.R. China) and another in developed country (New York City, USA), are selected for inter-comparison. The study reveals that aerosol effects on surface temperature depends largely on aerosols' optical and chemical properties as well as atmosphere and land surface conditions, such as humidity and land cover. Therefore, the actual magnitudes of aerosol effects differ from city to city. Aerosol measurements from AERONET show both average and extreme cases for aerosol impacts on surface insolation. In general, aerosols reduce surface insolation by 30Wm-2. Nevertheless, in extreme cases, such reduction can exceed 100 Wm-2. Consequently, this reduces surface skin temperature 2-10C in an urban environment.

A43C-1415 

Measurements of Area Resolved Surface Spectral Albedo and Validation of MODIS Land Albedo Product during MILAGRO, GoMACCS, and TC4

* Coddington, O (odele.coddington@lasp.colorado.du), University of Colorado Laboratory for Atmospheric and Space Physics, Campus Box 392, Boulder, CO 80309-0392, United States Schmidt, K S (sebastian.schmidt@lasp.colorado.edu), University of Colorado Laboratory for Atmospheric and Space Physics, Campus Box 392, Boulder, CO 80309-0392, United States Pilewskie, P (peter.pilewskie@lasp.colorado.edu), University of Colorado Laboratory for Atmospheric and Space Physics, Campus Box 392, Boulder, CO 80309-0392, United States Gore, W J (wgore@mail.arc.nasa.gov), NASA Ames Research Center, Mail Stop 245-4, Moffett Field, CA 94035-1000, United States Bergstrom, R W (bergstrom@baeri.org), Bay Area Environmental Research Institute, 560 Third St. West, Sonoma, CA 95476, United States Roman, M (mroman@bu.edu), Boston University Department of Geography and Center for Remote Sensing, 675 Commonwealth Avenue, Boston, MA 02215, United States Redemann, J (jredemann@mail.arc.nasa.gov), Bay Area Environmental Research Institute, 560 Third St. West, Sonoma, CA 95476, United States Russell, P B (Philip.B.Russell@nasa.gov), NASA Ames Research Center, Mail Stop 245-4, Moffett Field, CA 94035-1000, United States Liu, J (jcliu@bu.edu), Boston University Department of Geography and Center for Remote Sensing, 675 Commonwealth Avenue, Boston, MA 02215, United States Schaaf, C (schaaf@bu.edu), Boston University Department of Geography and Center for Remote Sensing, 675 Commonwealth Avenue, Boston, MA 02215, United States

Surface spectral albedo, a factor that strongly affects Earth's radiation balance, is a boundary condition which needs to be known with high accuracy for aerosol remote sensing, surface aerosol forcing, and radiative transfer calculations. We use Solar Spectral Flux Radiometer (SSFR) measurements of upward and downward irradiance to determine the area resolved surface spectral albedo (along the aircraft flight track) over the wavelength range between 350 and 2100 nm. Atmospheric measurements (altitude, pressure, temperature, relative humidity, aerosol loading, and aerosol optical properties) are used as inputs into an SSFR specific radiative transfer model. The model is then used iteratively in conjunction with the SSFR measurements to determine the contribution of the atmospheric layer between the flight altitude and the surface to the measured surface spectral albedo. Area resolved surface albedo results will be shown for case studies in three field campaigns where the SSFR was integrated on aircraft platforms: Megacity Initiative: Local and Global Research Observations (MILAGRO), Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS), and Tropical Composition, Cloud and Climate Coupling (TC4). Comparisons between the surface spectral albedo derived by the SSFR, the ground-based Multi-Filter Rotating Shadowband Radiometer (MFRSR), and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the NASA-EOS Terra and Aqua satellites will be shown.

A43C-1416 

In Situ Measurements of Black Carbon Aerosol During the 2006 Texas Air Quality Study

* Spackman, J R (ryan.spackman@noaa.gov), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States * Spackman, J R (ryan.spackman@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States Schwarz, J P), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Schwarz, J P), Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States Gao, R S), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Watts, L A), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Watts, L A), Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States Thomson, D S), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Thomson, D S), Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States Fahey, D W), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Holloway, J S), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Holloway, J S), Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States Peischl, J), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Peischl, J), Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States Ryerson, T B), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States Trainer, M K), National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, United States

In situ measurements of black carbon (BC) aerosol were acquired on 17 flights during the 2006 Texas Air Quality Study (TexAQS) with a Single-Particle Soot Photometer (SP2) operating aboard the NOAA WP-3D research aircraft. BC mass mixing ratios decrease by about 3 orders of magnitude from the polluted boundary layer to the clean middle troposphere, based on the particle size range of 0.1 to 0.6 μm volume-equivalent diameter, representing approximately 90% of the BC mass distribution. BC spans the range from 1000 ng/kg in the polluted boundary layer to less than 1 ng/kg in the clean middle troposphere. Furthermore, BC varies by about 2 orders of magnitude at any given altitude over the course of the mission. Simultaneous measurements of BC and carbon monoxide (CO) are positively correlated throughout the lower and middle troposphere. While the relationship between BC and CO is linear and compact for background tropospheric air, the correlation changes near BC source regions, with different signatures for the Houston urban, ship channel and biomass burning plumes. We examine the large variance in BC mass loadings, particularly at higher values of CO. A major implication of this work is that measurements of CO cannot be reliably used to estimate BC mass loadings in polluted urban environments.

A43C-1417 

Aerosol Properties and Radiative Forcing over Mega-cities in China

* Li, Z (zli@atmos.umd.edu), University of Maryland, 2207 CSS Bldg, College Park, MD 20742, United States

As the fastest and largest developing country in the world, China is experiencing rapid environmental changes. High concentrations of aerosols with diverse properties are emitted in the region, providing a unique opportunity for understanding the impact of environmental changes on climate. Until very recently, few observational studies were conducted in this important source region. The East Asian Study of Tropospheric Aerosols: an International Regional Experiment (EAST-AIRE) attempts to characterize the physical, optical and chemical properties of the aerosols and their effects on climate over China. Some preliminary results will be presented using continuous high-quality measurements of aerosol, cloud and radiative quantities made at the EAST-AIRE baseline stations near two mega cities (Beijing and Shanhai) in northern and southern China. Both regions are often covered by a thick layer of haze (with a yearly mean aerosol optical depth 0.7-0.8) due primarily to anthropogenic emissions of moderately strong absorbing aerosols, leading exceptionally large aerosol radiative forcing. http://www.atmos.umd.edu/~zli/EAST-AIRE/station.htm

A43C-1418 

Dynamics of the Optical Properties of Fine/Coarse Mode Aerosol Mixtures in Diverse Environments

* Eck, T F (teck@ltpmail.gsfc.nasa.gov), NASA/GSFC, Greenbelt Road, Greenbelt, MD 20771, United States Holben, B N (bholben@pop900.gsfc.nasa.gov), NASA/GSFC, Greenbelt Road, Greenbelt, MD 20771, United States Sinyuk, A (asiniuk@ltpmailx.gsfc.nasa.gov), NASA/GSFC, Greenbelt Road, Greenbelt, MD 20771, United States Pinker, R T (pinker@atmos.umd.edu), University of Maryland, Space Sciences Building, College Park, MD 20742, Goloub, P (Philippe.Goloub@loa.univ-lille1.fr), Université des Sciences et Technologies de Lille, Laboratoire d'Optique Amosphérique - Bât P5, Villeneuve d'Ascq, 59655, France Chen, H (chb@mail.iap.ac.cn), Chinese Academy of Sciences, P.O. Box 9804, Beijing, 100029, China Chatenet, B (chatenet@lisa.univ-paris12.fr), Université Paris, 61 Avenue du Général de Gaulle, Paris, 94010, France Singh, R P (rpiitkanpur@gmail.com), Indian Institute of Technology, Department of Civil Engineering, Kanpur, 208 016, India Al Mandoos, A (AMandoos@das.ae), Dept. of Atmospheric Studies, Ministry of Presidential Affairs, Abu Dhabi, 51133, United Arab Emirates Reid, J S (jeffrey.reid@nrlmry.navy.mil), Naval Research Laboratory, 7 Grace Hopper Ave., Stop 2, Monterey, CA 93943-5502, United States Smirnov, A (asmirnov@aeronet.gsfc.nasa.gov), NASA/GSFC, Greenbelt Road, Greenbelt, MD 20771, United States

Several regions of the earth exhibit seasonal mixtures of fine and coarse mode aerosol types, which are challenging to characterize from satellite remote sensing. Over land the coarse mode aerosols originate primarily from arid regions, which generate airborne soil dust, and the primary fine mode sources are urban/industrial emissions of gases and particulates and also biomass burning. The recently developed AERONET Version 2 retrieval algorithm produces more accurate retrievals of particle size distribution when non-spherical particles (such as dust) are present and also more accurate spectral single scattering albedo due to improved specification of the earth surface bidirectional reflectance. We show comparison of AERONET Version 1 and 2 retrievals that exhibit differences and suggest significantly improved single scattering albedo in Version 2. AERONET almucantar retrievals from several years are analyzed for the urban sites of Beijing, China and Kanpur, India (in the Ganges floodplain) where seasonal coarse mode dust particles mix with fine mode pollution aerosol, predominately in the spring. Additionally we compare multi-year data from Ilorin, Nigeria where desert dust from the Sahara and Sahel mix with fine mode biomass-burning aerosols. We also analyze data from two sites in the United Arab Emirates where dust mixes with urban/industrial pollution largely from petroleum industry emissions. The data are analyzed as a function of the aerosol optical depth fine mode fraction and also by Angstrom exponent, with comparisons made between sites.

A43C-1419 

Enhanced UV Absorption in Carbonaceous Aerosols during MILAGRO and Identification of Potential Organic Contributors.

* Mangu, A (axmangu@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Kelley, K L (kxbrock@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Marchany-Rivera, A (angierosy@gmail.com), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Kilaparty, S (kspramila@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Gunawan, G (gxgunawan@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Gaffney, J S (jsgaffney@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Marley, N A (namarley@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States

Measurements of aerosol absorption were obtained as part of the MAX-Mex component of the MILAGRO field campaign at site T0 (Instituto Mexicano de Petroleo in Mexico City) during the month of March, 2006 by using a 7- channel aethalometer (Thermo-Anderson). These measurements, obtained at 370, 470, 520, 590, 660, 880, and 950 nm at a 5 minute time resolution, showed an enhanced absorption in the UV over that expected from carbon soot alone. Samples of fine atmospheric aerosols (less than 0.1micron) were also collected at site T0 and T1 (Universidad Technologica de Tecamac, State of Mexico) from 5 am to 5 pm (day) and from 5 pm to 5 am (night) during the month of March 2006. The samples were collected on quartz fiber filters with high volume impactor samplers. The samples have been characterized for total carbon content (stable isotope ratio mass spectroscopy) and natural radionuclide tracers (210Pb, 210Po, 210Bi, 7Be, 13C, 14C, 40K, 15N). Continuous absorption spectra of these aerosol samples have been obtained in the laboratory from 280 to 900nm with the use of an integrating sphere coupled to a UV-visible spectrometer (Beckman DU with a Labsphere accessory). The integrating sphere allows the detector to collect and spatially integrate the total radiant flux reflected from the sample and therefore allows for the measurement of absorption on highly reflective or diffusely scattering samples (1). The continuous spectra also show an enhanced UV absorption over that expected from carbon soot and the general profiles are quite similar to those observed for humic and fulvic acids found as colloidal materials in surface and groundwaters (2), indicating the presence of humic-like substances (HULIS) in the fine aerosols. The spectra also show evidence of narrow band absorbers below 400 nm typical of polycyclic aromatics (PAH) and nitrated aromatic compounds. Spectra were also obtained on NIST standard diesel soot (SRM 2975), NIST standard air particulate matter (SRM 8785), and nitrated PAH compounds for comparison. Potential organic aerosol components are identified which contribute to the enhanced absorption observed in the field. The wavelength dependence of the mass specific absorption is obtained from these spectra and total carbon measurements. The wavelength dependence of the aerosol complex refractive index (m = n +ik) in the UV-visible spectral region is determined by application of the Kramers Kronig function. The importance of the aerosol absorption in the infrared spectral region to radiative forcing will be discussed. 1. Marley, N.A., J.S. Gaffney, J.C. Baird, C.A. Blazer, P.J. Drayton, and J.E. Frederick, Aerosol Sci. Technol., 34, 535-549, (2001). 2. N.A. Marley, J.S. Gaffney, and K.A. Orlandini, Chapter 7 in Humic/Fulvic Acids and Organic Colloidal Materials in the Environment, ACS Symposium Series 651, American Chemical Society, Washington, D.C., pp. 96-107, 1996. This work was conducted as part of the Department of Energy's Atmospheric Science Program as part of the Megacity Aerosol Experiment – Mexico City during MILAGRO. This research was supported by the Office of Science (BER), U.S. Department of Energy Grant No. DE-FG02-07ER64329. We also wish to thank Mexican Scientists and students for their assistance from the Instituto Mexicano de Petroleo (IMP) and CENICA.

A43C-1420 

Evidence for Biomass Burning from 14C and 13C/12C Measurements at T-0 and T-1 during MILAGRO.

* Gaffney, J S (jsgaffney@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72204, United States Marley, N A (namarley@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72204, United States Tackett, M J (mjtackett@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72204, United States Sturchio, N C (sturchio@uic.edu), University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, United States Heraty, L J (lheraty@uic.edu), University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, United States Martinez, N (namartin@nsf.gov), University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, United States Hardy, K (kavita.hardy@gmail.com), Swarthmore College, 500 College Ave., Swarthmore, PA 19081, United States Guilderson, T (tguilderson@llnl.gov), Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, United States

Both stable carbon isotopic and radiocarbon characterizations of aerosols can yield important information regarding the sources of carbonaceous aerosols in urban and regional environments. Biomass derived materials are labeled due to their recent photochemical activity in radiocarbon and vary depending upon the photochemical pathway (either C-4 or C-3) in stable carbon-13 content. C-4 being enriched over C-3. During the MILAGRO campaign, quartz filter samples were taken at 12 hour intervals from 5 am to 5 pm (day) and from 5 pm to 5 am (night) during the month of March 2006. These samples were taken at the two super-sites, T-0 (Instituto Mexicano de Petroleo in Mexico City) and T-1 (Universidad Technologica de Tecamac, State of Mexico). The total carbon content was analyzed for stable carbon isotopic composition as well as for radiocarbon. Stable isotope mass spectroscopy was used to determine the carbon-13 to carbon-12 isotopic ratios on carbon dioxide. The carbon dioxide was then converted to graphite for analysis by accelerator mass spectrometry at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory. Results are presented for the carbon-13 content relative to the PDB standard and radiocarbon is given relative to recent carbon. The results for total radiocarbon content show that the carbonaceous aerosol content in Mexico City has more than half of the carbon coming from biomass derived sources. These can include inflow of biomass burning aerosols into the T-0 site as well as the input from local burning of biofuels and trash containing biomass derived materials (paper, boxes, etc.). Data also indicate that at the T-1 site biomass burning of C-4 grasses appears to be significant in that the carbon-13 values observed are enriched. Also at T-1 the radiocarbon levels are also found to be slightly higher indicating regional biomass burning as a significant contributor to aerosol carbon in the 0.1 to 1.0 micron size fraction. Some day and night differences were observed that indicate secondary organic aerosols are contributing and that a significant fraction of these aerosols are biomass derived. Further analyses of organic carbon and elemental carbon fractions are underway. This work was performed as part of the Department of Energy's Megacity Aerosol Experiment - Mexico City (MAX- Mex) under the support of the Atmospheric Science Program. This research was supported by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-07ER64328.

A43C-1421 

Aerosol Angstrom Absorption Coefficient Comparisons during MILAGRO.

* Marley, N A (namarley@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Marchany-Rivera, A (angierosy@gmail.com), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Kelley, K L (kxbrock@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Mangu, A (axmangu@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Gaffney, J S (jsgaffney@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States

Measurements of aerosol absorption were obtained as part of the MAX-Mex component of the MILAGRO field campaign at site T0 (Instituto Mexicano de Petroleo in Mexico City) by using a 7-channel aethalometer (Thermo- Anderson) during the month of March, 2006. The absorption measurements obtained in the field at 370, 470, 520, 590, 660, 880, and 950 nm were used to determine the aerosol Angstrom absorption exponents by linear regression. Since, unlike other absorbing aerosol species (e.g. humic like substances, nitrated PAHs), black carbon absorption is relatively constant from the ultraviolet to the infrared with an Angstrom absorption exponent of -1 (1), a comparison of the Angstrom exponents can indicate the presence of aerosol components with an enhanced UV absorption over that expected from BC content alone. The Angstrom exponents determined from the aerosol absorption measurements obtained in the field varied from – 0.7 to – 1.3 during the study and was generally lower in the afternoon than the morning hours, indicating an increase in secondary aerosol formation and photochemically generated UV absorbing species in the afternoon. Twelve-hour integrated samples of fine atmospheric aerosols (<0.1micron) were also collected at site T0 and T1 (Universidad Technologica de Tecamac, State of Mexico) from 5 am to 5 pm (day) and from 5 pm to 5 am (night) during the month of March 2006. Samples were collected on quartz fiber filters with high volume impactor samplers. Continuous absorption spectra of these aerosol samples have been obtained in the laboratory from 280 to 900nm with the use of an integrating sphere coupled to a UV spectrometer (Beckman DU with a Labsphere accessory). The integrating sphere allows the detector to collect and spatially integrate the total radiant flux reflected from the sample and therefore allows for the measurement of absorption on highly reflective or diffusely scattering samples. These continuous spectra have also been used to obtain the aerosol Angstrom absorption exponents by linear regression over the entire UV-visible spectral range. These results are compared to results obtained from the absorbance measurements obtained in the field. The differences in calculated Angstrom absorption exponents between the field and laboratory measurements are attributed partly to the differences in time resolution of the sample collection resulting in heavier particle pileup on the filter surface of the 12-hour samples. Some differences in calculated results can also be attributed to the presence of narrow band absorbers below 400 nm that do not fall in the wavelengths covered by the 7 wavelengths of the aethalometer. 1. Marley, N.A., J.S. Gaffney, J.C. Baird, C.A. Blazer, P.J. Drayton, and J.E. Frederick, "The determination of scattering and absorption coefficients of size-fractionated aerosols for radiative transfer calculations." Aerosol Sci. Technol., 34, 535-549, (2001). This work was conducted as part of the Department of Energy's Atmospheric Science Program as part of the Megacity Aerosol Experiment – Mexico City during MILAGRO. This research was supported by the Office of Science (BER), U.S. Department of Energy Grant No. DE-FG02-07ER64329. We also wish to thank Mexican Scientists and students for their assistance from the Instituto Mexicano de Petroleo (IMP) and CENICA.

A43C-1422 

Aerosol Light Absorption and Scattering in Mexico City: Comparison With Las Vegas, NV, and Los Angeles, CA.

* Paredes-Miranda, G (gparedes@physics.unr.edu), Department of Physics, University of Nevada Reno, 1664 N. Virginia St., Reno, NV 89557- 0042, United States Arnott, W P (patarnott@physics.unr.edu), Department of Physics, University of Nevada Reno, 1664 N. Virginia St., Reno, NV 89557- 0042, United States Gaffney, J S (jsgaffney@ualr.edu), Department of Chemistry and Graduate Research Institute, University of Arkansas Chemistry 2801 South University Avenue SCLB RM 451, Little Rock, AR 72204, United States Marley, N A (namarley@ualr.edu), Department of Chemistry and Graduate Research Institute, University of Arkansas Chemistry 2801 South University Avenue SCLB RM 451, Little Rock, AR 72204, United States Campbell, D (Dave.Campbell@dri.edu), Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, United States Fujita, E (Erik.Fujita@dri.edu), Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, United States

Aerosol light scattering and absorption measurements were deployed in and near Mexico City in March 2006 as part of the Megacity Impacts on Regional and Global Environments (MIRAGE). The primary site in Mexico City was an urban site at Instituto Mexicano del Petroleo (Mexican Oil Institute, denoted by IMP). Similar campaigns were held in Las Vegas, NV in January-February, 2003; and Los Angeles, CA at numerous sites during all seasons from 2003 through 2007. The IMP site gave in-situ characterization of the Mexico City plume under favorable wind conditions. The photoacoustic instrument (PAS) used at IMP operates at 532 nm, and conveniently allowed for characterization of gaseous absorption at this wavelength as well. Light scattering measurements are accomplished within the PAS by the reciprocal nephelometery method. In Mexico City the aerosol absorption coefficient typically varies between 20 and 180 Mm^-1 during the course of the day and significant diurnal variation of the aerosol single scattering albedo was observed probably as a consequence of secondary aerosol formation. We will present the diurnal variation of the scattering and absorption as well as the single scattering albedo and fraction of absorption due to gases at the IMP site and compare with Las Vegas diurnal variation. Mexico City ‘breaths' more during the course of the day than Las Vegas, Nevada in part because the latitude of Mexico City resulted in more direct solar radiation. Further insight on the meteorological connections and population dynamics will be discussed.

A43C-1423 

Infrared Absorption by Atmospheric Aerosols in Mexico City during MILAGRO.

* Kelley, K L (kxbrock@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Mangu, A (axmangu@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Gaffney, J S (jsgaffney@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States Marley, N A (namarley@ualr.edu), University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States

Past research in our group using cylindrical internal reflectance spectroscopy has indicated that aqueous aerosols could contribute to the radiative warming as greenhouse species (1,2). Although aerosol radiative effects have been known for sometime and are considered one of the major uncertainties in climate change modeling, most of the studies have focused on the forcing due to scattering and absorption of radiation in the uv- visible region (3). Infrared spectral information also allows the confirmation of key functional groups that are responsible for enhanced absorption observations from secondary organics in the uv-visible region. This work extends our efforts to evaluate the infrared absorption by aerosols, particularly organics, that are now found to be a major fraction of urban and regional aerosols in the 0.1 to 1.0 micron size range and to help identify key types of organics that can contribute to aerosol absorption. During the MILAGRO campaign, quartz filter samples were taken at 12-hour intervals from 5 am to 5 pm (day) and from 5 pm to 5 am (night) during the month of March 2006. These samples were taken at the two super-sites, T-0 (Instituto Mexicano de Petroleo in Mexico City) and T-1 (Universidad Technologica de Tecamac, State of Mexico). The samples have been characterized for total carbon content (stable isotope mass spectroscopy) and natural radionuclide tracers, as well as for their UV-visible spectroscopic properties by using integrating sphere diffuse reflectance spectroscopy (Beckman DU with a Labsphere accessory). These same samples have been characterized in the mid and near infrared spectral ranges using diffuse reflection spectroscopy (Nicolet 6700 FTIR with a Smart Collector accessory). Aerosol samples were removed from the surfaces of the aerosol filters by using Si-Carb sampler. The samples clearly indicate the presence of carbonyl organic constituents and the spectra are quite similar to those observed for humic and fulvic acids found as colloidal materials in surface and groundwaters (4). Examples of the IR spectra obtained and variance as a function of time at the two sites will be presented. The spectra are taken in Kubelka – Munk format, which also allows the infrared absorption strengths to be evaluated as function of wavelength. The wavelength dependence of the aerosol complex refractive index (m = n + ik) in the infrared spectral region is determined by application of the Kramers Kronig function. The importance of the aerosol absorption in the infrared spectral region to radiative forcing will be discussed. 1. N.A. Marley, J.S. Gaffney, and M.M. Cunningham,Environ. Sci. Technol. 27 2864-2869 (1993). 2. N.A. Marley, J.S. Gaffney, and M.M. Cunningham, Spectroscopy 7 44-53 (1992). 3. J.S. Gaffney and N.A. Marley, Atmospheric Environment, New Directions contribution, 32, 2873-2874 (1998). 4. N.A. Marley, J.S. Gaffney, and K.A. Orlandini, Chapter 7 in Humic/Fulvic Acids and Organic Colloidal Materials in the Environment, ACS Symposium Series 651, American Chemical Society, Washington, D.C., pp. 96-107, 1996. This work was performed as part of the Department of Energy's Megacity Aerosol Experiment - Mexico City (MAX- Mex) under the support of the Atmospheric Science Program. This research was supported by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-07ER64328.

A43C-1424 

Hygroscopic Properties and Wavelength Dependence of Light Extinction of Aerosols as measured by Cavity Ring-Down Spectrometry (CRD-AES) during the TeXAQS-GoMACCS 2006 study

* Massoli, P (Paola.Massoli@noaa.gov), CIRES, University of Colorado, Boulder, CO 80309, United States * Massoli, P (Paola.Massoli@noaa.gov), NOAA ESRL/CSD, 325 Broadway, Boulder, CO 80305, United States Baynard, T (Tahllee.Baynard@comcast.net), CIRES, University of Colorado, Boulder, CO 80309, United States Baynard, T (Tahllee.Baynard@comcast.net), NOAA ESRL/CSD, 325 Broadway, Boulder, CO 80305, United States Lack, D (Daniel.Lack@noaa.gov), CIRES, University of Colorado, Boulder, CO 80309, United States Lack, D (Daniel.Lack@noaa.gov), NOAA ESRL/CSD, 325 Broadway, Boulder, CO 80305, United States Bates, T (Tim.Bates@noaa.gov), NOAA PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, United States Quinn, P (Patricia.K.Quinn@noaa.gov), NOAA PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, United States Lovejoy, E (Edward.R.Lovejoy@noaa.gov), NOAA ESRL/CSD, 325 Broadway, Boulder, CO 80305, United States Brock, C (Charles.A.Brock@noaa.gov), CIRES, University of Colorado, Boulder, CO 80309, United States Brock, C (Charles.A.Brock@noaa.gov), NOAA ESRL/CSD, 325 Broadway, Boulder, CO 80305, United States Ravishankara, A (A.R.Ravishankara@noaa.gov), NOAA ESRL/CSD, 325 Broadway, Boulder, CO 80305, United States

Light extinction coefficient, optical depth, single scattering albedo and asymmetry parameter are the key optical properties that determine the influence of aerosols on climate via scattering and absorption of incoming solar radiation, i.e., direct effect. These properties vary with the wavelength and are also strong function of the ambient relative humidity. Size and refractive index of aerosols can change significantly if the aerosols are hygroscopic. Accurate estimate of the relative humidity dependence of extinction is critical to properly quantify the effects of aerosols on climate and on visibility changes (i.e., air quality). A Cavity Ring-Down Aerosol Extinction Spectrometer (CRD-AES), developed at NOAA ESRL, was deployed on the RV R.H.Brown during the TEXAQS- GoMACCS 2006 study in the Gulf of Mexico to characterize the local and regional aerosols and to assess their impact on air quality and climate. Aerosol extinction at 355, 532, and 1064 nm for sub-1 micron and coarse size aerosols were measured at different relative humidity. Further, a Photoacoustic Absorption Spectrometer (PAS) that measures light absorption by aerosols was coupled to the CRD-AES to determine aerosol single scattering albedo at 532 nm. Here we present the humidity dependence (gamma), single scattering albedo and Angstrom exponent for a selection of aerosol types with varying chemical composition. Fresh local emissions (such as ship plumes and urban aerosols) appear to be hydrophobic, whereas regional and continental aerosols exhibit some variability, likely due to the degree of mixing and transformation during transport. These data are discussed with special emphasis on the proper treatment of the variation of the optical properties with relative humidity, critical for radiative models to better estimate the aerosol forcing on climate.

A43C-1425 

Contribution of Primary and Secondary Organic Aerosol to Global Cloud Condensation Nuclei Concentrations

* Trivitayanurak, W (win@cmu.edu), Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States Adams, P J (peteradams@cmu.edu), Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States Adams, P J (peteradams@cmu.edu), Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA 15213, United States

Cloud condensation nuclei (CCN) prediction is the key to estimating aerosol indirect effects, which remain very uncertain. A significant fraction of CCN is organic aerosol (OA) originating from both primary and secondary sources, and the relative contribution of primary organic aerosol (POA) and secondary organic aerosol (SOA) to the overall organic aerosol budget is still controversial. Even if total OA levels can be well described in models, different microphysical processes form SOA than POA, thereby affecting aerosol size distributions and CCN concentrations. A global aerosol model is used to study the sensitivity of POA versus SOA to CCN concentrations. This work develops further the TwO-Moment Aerosol Sectional (TOMAS) global aerosol microphysical model (Adams and Seinfeld, 2002), which was integrated into the GEOS-CHEM model, a global three-dimensional tropospheric chemistry-transport model (Bey et al., 2001). The TOMAS model conserves both number and mass concentrations of aerosol segregated into 30 size bins from 0.01 μm to 10 μm. The microphysical processes include coagulation, condensation, evaporation, nucleation, size-resolved wet deposition and size- resolved dry deposition. In this work, a simulation of elemental carbon (EC), primary organic aerosol (POA), and secondary organic aerosol (SOA) is added to the model, which previously included sulfate and sea-salt aerosols. TOMAS predicted aerosol number, carbonaceous mass concentrations, and size distributions are compared with observational data from a variety of field campaigns. Year-round observations from various sites are used in the comparison to test the model ability to reproduce the observed seasonality. Additionally, we explore the contribution of secondary organic aerosol to global CCN. By varying the fraction of SOA within the total OA source, we can examine how it affects CCN production. The findings will shed some light on the range of uncertainty resulting from the currently uncertain tropospheric SOA levels.

A43C-1426 

Measurements of Intensive Aerosol Optical Properties During TexAQS II

* Atkinson, D B (AtkinsonD@pdx.edu), Chemistry Department Portland State University, P.O. Box 751, Portland, OR 97207-0751, United States Radney, J G (JRadney@pdx.edu), Chemistry Department Portland State University, P.O. Box 751, Portland, OR 97207-0751, United States Wright, M E (wrightm@pdx.edu), Chemistry Department Portland State University, P.O. Box 751, Portland, OR 97207-0751, United States

Time-resolved measurements of the bulk extensive aerosol optical properties - particle extinction coefficient (b_ext) and particle scattering coefficient (b_scat) - and particle number concentrations were made as part of the six-week TRAMP experiment during the TexAQS II (2006) study. These measurements were done at a nominal surface site (the roof of an 18 story building) on the University of Houston campus near downtown Houston, Texas. Our ground-based tandem cavity ring-down transmissometer/nephelometer instrument (CRDT/N) provided the aerosol optical property measurements. A commercial Condensation Particle Counter (TSI 3007) was used to measure the number concentrations during part of the study period. The optical data was used to construct the intensive aerosol optical properties single scattering albedo ω₀ at 532 nm and the Angstrom exponent for extinction between 532 nm and 1064 nm. Recent validation studies of size- selected laboratory generated aerosols are presented to illustrate the soundness of this approach using our instrument. The Angstrom exponent is compared to values from other instruments operating in the area and is found to be a characteristic of the regional air mass under some conditions. Size distributions measured during the study were used to create a new empirical adjustment to scattering measured by the Radiance Research nephelometer, resulting in improved results for particle absorption coefficient and single scattering albedo. The study average value of ω₀(532 nm) = 0.78 is lower than expected from comparable field studies and even lower values are experienced during the study. Possible causes of this discrepancy are examined and the utility of using the current version of the CRDT/N instrument to measure the key radiative property ω₀ is assessed. Observed episodes of rapid increases in particle number concentration with little corresponding growth in the optical properties can presumably be used to signal the occurrence of particle nucleation or growth via gas-phase condensation. These results may be confirmed by other data taken during the TRAMP experiment. These results will be discussed in the context of aerosol effects on regional and larger scale climate.

A43C-1427 

Vertical aerosol structure and aerosol mixed layer heights determined with scanning shipborne lidars during the TexAQS II study

* McCarty, B J (brandi.mccarty@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Senff, C J (christoph.senff@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Tucker, S C (sara.tucker@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Eberhard, W L (wynn.eberhard@noaa.gov), NOAA Earth Systems Research Laboratory, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Marchbanks, R D (richard.marchbanks@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Machol, J (janet.machol@noaa.gov), Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Brewer, W A (alan.brewer@noaa.gov), NOAA Earth Systems Research Laboratory, R/CSD3, 325 Broadway, Boulder, CO 80305, United States

The NOAA Earth Systems Research Laboratory (ESRL) deployed the Ozone Profiling Atmospheric LIDAR (OPAL) on the R/V Ronald H. Brown during the summer of 2006 for the Texas Air Quality Study (TEXAQS II). Calibrated aerosol backscatter profiles were determined from data collected at the 355 nm wavelength using a modified Klett retrieval method. OPAL employs a unique scan sequence that consists of staring at multiple elevation angles between 2 and 90 degrees, which is repeated approx. every 90 sec. Blending the data from the various elevation angles allows to extend the aerosol backscatter profiles down to near the surface (approximately 10 meters ASL), while maintaining a high spatial resolution (5 meters). Successful application of this technique requires the aerosol distribution to be sufficiently horizontally homogeneous over several kilometers. Estimates of aerosol mixed layer height were determined by applying a Haar wavelet transform method to detect the gradient that is often present at the top of the boundary layer. Co-located on the R/V Ronald H. Brown, was NOAA/ESRL's High Resolution Doppler LIDAR (HRDL). Aerosol mixed layer heights were also estimated using the data from the 2 micron Doppler LIDAR. A comparison of the mixed layer heights as determined from each LIDAR's observations was used to choose the height of the layer likely connected with the surface. The vertical structure of aerosols in the lower troposphere, in particular the presence of aerosol layers above the boundary layer, is important in understanding radiative effects of aerosols. We will present aerosol backscatter structure in the lower troposphere encountered during the TexAQS II study as well as a comparison of relative aerosol content in the free troposphere compared to that within the boundary layer.

A43C-1428 

Comparison of LIDAR and Cavity Ring-Down Measurements of Aerosol Extinction and Study of Inferred Aerosol Gradients

* Eberhard, W L (Wynn.Eberhard@noaa.gov), NOAA Earth System Research Laboratory, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Massoli, P (Paola.Massoli@noaa.gov), Cooperative Institute for Research in Environmental Science, University of Colorado / NOAA, R/CSD2, 325 Broadway, Boulder, CO 80305, United States McCarty, B J (Brandi.McCarty@noaa.gov), Cooperative Institute for Research in Environmental Science, University of Colorado / NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Machol, J L (Janet.Machol@noaa.gov), Cooperative Institute for Research in Environmental Science, University of Colorado / NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States Tucker, S C (Sara.Tucker@noaa.gov), Cooperative Institute for Research in Environmental Science, University of Colorado / NOAA, R/CSD3, 325 Broadway, Boulder, CO 80305, United States

A LIDAR and a Cavity Ring-Down Aerosol Extinction Spectrometer (CRD) instrument simultaneously measured aerosol extinction at 355-nm wavelength from aboard the Research Vessel Ronald H. Brown during the Texas Air Quality Study II campaign. The CRD measured air sampled from the top of the common mast used by several in situ aerosol optical and chemical instruments. The LIDAR's scan sequence included near-horizontal stares (2° elevation angle) with pointing corrected for ship's roll. Aerosol extinction was retrieved using a variant of the slope method. The LIDAR therefore sampled air over a short vertical extent with midpoint higher above the surface than the CRD intake and at a horizontal distance of as much as a few kilometers. The CRD measured aerosol extinction at dry and at high (near-ambient) relative humidity (RH) levels, which were used to scale the measurements to ambient RH for the comparisons. Data from the two instruments for well-mixed conditions (supported by turbulence and atmospheric stability data) are compared to evaluate the degree of agreement between the two methods and reasons for differences. For instances of larger differences, the aerosol gradient below approximately 100 m altitude is inferred and examined in context of low-level meteorological parameters and LIDAR measurements at higher angles.

A43C-1429 

Sahelian dust lifting in the inter-tropical discontinuity region: Lidar observations and mesoscale modelling

* BOU KARAM, D (diana@aero.jussieu.fr), Service d'Aerono mie / CNRS, Tour 45/46, 3° Etage 4 Place Jussieu, Paris, 75005, France Flamant, C (cyf@aero.jussieu.fr), Service d'Aerono mie / CNRS, Tour 45/46, 3° Etage 4 Place Jussieu, Paris, 75005, France Tulet, P (Pierre.Tulet@cnrm.meteo.fr), Meteo-France, CNRM/GMEI, 42, Avenue de Coriolis, Toulouse, 31000, France Chaboureau, J (Jean-Pierre.Chaboureau@aero.obs-mip.fr), Laboratoire d'Aerologie, UPS and CNRS, 42, Avenue de Coriolis, Toulouse, 31000, France Dabas, A (Alain.Dabas@cnrm.meteo.fr), Meteo-France, CNRM/GMEI, 42, Avenue de Coriolis, Toulouse, 31000, France Chong, M (Michel.Chong@aero.obs-mip.fr), Laboratoire d'Aerologie, UPS and CNRS, 42, Avenue de Coriolis, Toulouse, 31000, France Reitebuch, O (Oliver.Reitebuch@dlr.de), Deutsches Zentrum für Luft- und Raumfahrt, Wessling, Wessling, 99999, Germany

Airbone lidar observations acquired with the LEANDRE 2 system during 3 flights of the SAFIRE Falcon 20 in the framework of the AMMA Special Observing Period (SOP) 2a1 (July 2006) over western Niger, revealed the existence of desert dust uptakes in the region of the inter-tropical discontinuity (ITD) in the morning hours. Complementary observations provided by dropsondes released from the same platform as well as airborne wind measurements made from another platform (the DLR Falcon 20, flying in coordination with the SAFIRE Falcon 20) evidenced that the lifting was associated with the leading edge of the monsoon low level jet, and to be transported southward by the harmattan, above the monsoon layer. A 10-day numerical simulation, using the mesoscale model Meso-NH (including the dust emission box Dust Entrainment And Deposition model), was conducted to assess the representativity of the observed phenomenon as well as the mechanisms associated with the Sahelian dust emissions. The Meso-NH simulation (initialized by and nudged with ECMWF analyses) was carried out on a 2000 km x 2000 km domain (20-km horizontal resolution) centered at 20°N and 7°E, that included the Falcons flight track, as well as numerous AMMA-related ground-based measurement sites (Tamanrasset, Agadez, Niamey/Banizoumbou, etc..) for validation purposes. In the simulation, large dust uptakes associated with the leading edge of the monsoon flow, with a dust concentration reaching 2000μg/m3, and to be transported southward by the harmattan, above the monsoon layer, were well reproduced. On the other hand, the simulation suggested the existence of dust emissions associated with the harmattan flow which were not observed by airborne lidar measurements. The reason for the discrepancy between the model results and the lidar observations is investigated.

A43C-1430 

Light Absorption by Organic Carbon From Wood Combustion

* Chen, Y (chen63@uiuc.edu), Department of Civil and Environmental Engineering, University of Illinois at Urbana- Champaign, 205 North Mathews Ave., Urbana, IL 61801, United States Roden, C A (croden@uiuc.edu), Department of Civil and Environmental Engineering, University of Illinois at Urbana- Champaign, 205 North Mathews Ave., Urbana, IL 61801, United States Bond, T C (yark@uiuc.edu), Department of Civil and Environmental Engineering, University of Illinois at Urbana- Champaign, 205 North Mathews Ave., Urbana, IL 61801, United States

Carbonaceous aerosols are prevalent in urban areas and affect the radiative balance of the Earth by absorbing and scattering light. Carbonaceous aerosol is composed of black carbon (BC) and various types of organic carbon (OC). It is well known that BC is the most absorbing aerosol in the atmosphere. Although the role of OC in light absorption has not been thoroughly investigated, some organic compounds also have significant absorption, which is greater at near-ultraviolet and blue wavelengths. Since visible absorption is far more important for the energy balance than ultraviolet absorption, to the extent that OC absorbs visible light, it may be a non-negligible contributor to direct aerosol radiative forcing. In this work, we examine primary BC and OC emitted from solid fuels, which provide about two-thirds of global primary organic aerosol emissions. Our work focuses on understanding the chemical composition and optical properties of these particles in order to better characterize them in models. Samples were generated in a laboratory combustion chamber at different burning conditions using softwood and hardwood, and collected on baked quartz filters. The filters were then extracted with deionized water and different organic solvents, including methanol, hexane and acetone. Light absorption of different sample solutions was tested at the wavelength from 190nm to 800nm. Absorption spectra of the extracts were measured with a Shimadzu UV-2401 UV-Vis recording spectrophotometer. Total carbon was measured with a Sunset OC/EC analyzer. Preliminary results showed that light absorption in visible spectrum was partially caused by water soluble organic carbon and another larger portion was caused by water insoluble organic carbon. The greatest absorption was that of acetone extracts, followed by that of methanol, hexane and water extracts. This suggests that chromophores are associated with compounds that are neither completely polar nor completely non-polar. In addition, high performance liquid chromatography (HPLC) combined with ultraviolet-visible spectroscopy identified the polarity of molecules associated with visible and near-ultraviolet absorption in the water-soluble fraction. We report relationships between these chemical analyses and climate-relevant aerosol properties, including total absorption per mass, absorption Angstrom exponent, and hygroscopicity.

A43C-1431 

Urban Heat Island Effect and its Impact on Boundary Layer Development and Land-Sea Circulation over Northern Taiwan

* Lin, C (yao435@rcec.sinica.edu.tw), Research Center for Environmental Changes, No.128, Sec.2, Academia RD., Taipei, 115, Taiwan Chen, F), National Center for Atmospheric Research, P.O. BOX 3000, Boulder, Colorado, 80307- 3000, Boulder, CO 80307, United States Huang, J), Research Center for Environmental Changes, No.128, Sec.2, Academia RD., Taipei, 115, Taiwan Liou, Y), Center for Space and Remote Sensing Research, No.300, Jhongda Rd,Jhongli city, Taoyuan, 32001, Taiwan Chen, W), Research Center for Environmental Changes, No.128, Sec.2, Academia RD., Taipei, 115, Taiwan Chen, W), Research Center for Environmental Changes, No.128, Sec.2, Academia RD., Taipei, 115, Taiwan

The impact of the urban heat island (UHI) effect on environmental phenomena and regional climate has been receiving wide attention in recent decades. Taiwan, especially Taipei (located in northern Taiwan), is experiencing a significant urban heat island effect due to its high population density and the uniqueness of the geographic structure. In order to evaluate the impacts of urbanization and UHI effect over northern Taiwan, a next generation mesoscale model, Weather Research and Forecasting (WRF) model coupled with the Noah land surface model and Urban canopy model (UCM), was used to study this issue. By using the WRF-Noah-UCM model, it has significantly improved our simulation results for the prediction of the UHI effect, boundary layer development, and land sea breeze. Observations of weather stations and Lidar showed that the near surface air temperature was nearly 34 -35¢XC and the boundary layer height was nearly 1500 m around noon in Taipei on 17 June 2006. Around midnight, the air temperature ranged from 26 to 28°C. Our model can predict well for boundary layer develop during the daytime and the urban heat island effect in northern Taiwan. Sensitivity tests indicate that the anthropogenic heat (AH) plays an important role for the boundary layer to develop and UHI intensity in the Taipei area, especially during night time and early morning. When we increase AH by 100 W/m2 in the model, the average surface temperature could increase nearly 0.3°C in Taipei. Furthermore, we found the UHI effect also has a significant impact on land sea circulation. It could enhance the sea breeze in the daytime and weaken the land breeze during the night time and thus had a significant impact on the air pollution diffusion in northern Taiwan.

A43C-1432 

Aerosol Optical Effects on Deep Convective Clouds and Radiative Forcing

* Fan, J (jiwen.fan@pnl.gov), Department of Atmospheric Sciences, Texas A&M University, 3150 TAMU, College Station, TX 77843-3150, United States Zhang, R (zhang@ariel.met.tamu.edu), Department of Atmospheric Sciences, Texas A&M University, 3150 TAMU, College Station, TX 77843-3150, United States Tao, W (tao@agnes.gsfc.nasa.gov), NASA Goddard Space Flight Center, Code 613.1, Greenbelt, MD 20771, United States Mohr, K I (mohr@atmos.albany.edu), University at Albany, SUNY, Department of Earth and Atmospheric Sciences, Albany, NY 12222,

Aerosols interact directly and indirectly with the Earth's radiation budget and climate. For the direct effect, aerosols scatter and absorb solar radiation. Light scattering by aerosols changes the radiative fluxes at the top-of- atmosphere (TOA), at the surface, and within the atmospheric column, while aerosol absorption modifies the atmospheric temperature structure, decreases the solar radiation at the surface, and lowers surface sensible and latent fluxes, suppressing convection and reducing cloud fraction. Using a two-dimensional cloud-resolving Goddard Cloud Ensemble (GCE) model coupled with radiative transfer processes and the land-atmosphere interaction processes, we investigate aerosol radiative effects on deep convective clouds in an urban atmospheric environment, focussing on the radiative effects of anthropogenic aerosols containing BC. An aerosol radiative module is developed to calculate the wavelength-dependent aerosol radiative properties based on the aerosol composition, size distribution, mixing state, and ambient relative humidity. The significance of the aerosol radiative effects (ARE) is investigated by comparing with the cases excluding the ARE. The associated aerosol direct, semi-direct and indirect radiative forcing for deep convective clouds are estimated, and the sensitivity of cloud properties and radiative forcing to aerosol single-scattering albedo (SSA) are examined. The results provide insight on the coupling between the aerosol direct, semi-direct, and indirect effects on clouds.

A43C-1433 

The role of Saharan dust in determining the first aerosol indirect effect

* Shao, H (hshao@fsu.edu), Florida State University, Meteorology Department, Tallahassee, FL 32306, Liu, G (liug@met.fsu.edu

Anthropogenic aerosols acting as cloud condensation nuclei affect Earth's radiative balance indirectly by changing cloud radiative properties. This so-called first aerosol indirect effect (AIE) has a potentially large but poorly quantified cooling effect. In modeling the aerosol indirect forcing, because the aerosol-cloud interaction is not resolved in global climate models (GCMs), cloud droplet number concentration is typically parameterized using an empirical relationship that directly relates droplet number concentration to aerosol number concentration based on the measurements between polluted and clean clouds. It is realized that the first AIE obtained in this way can be contaminated by the coherent variation in the pertinent variables such as cloud liquid water and the degree of entrainment mixing. However, the influence from changes in aerosol properties themselves has not received a deserved attention. Using satellite observations over eastern subtropical oceans, we show that over the north-eastern Atlantic the aerosols properties are distinct from the other regions due to the dust particles originating from Sahara desert. These dust particles may significantly reduce the efficiency of aerosols to act as cloud condensation nuclei. As a result, the locally observed first AIE from this region can be significantly deviated from global mean, even resulting in positive values. Because of the large areal fraction of this region, ignoring the influence from the northern Africa dust particles will underestimate the globally averaged first AIE approximately by half.

A43C-1434 

Aerosol-Cloud Interactions in the New York City Metropolitan Region

* Zhang, Y (yanzhang@princeton.edu), Princeton Unversity, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States Smith, J A (jsmith@princeton.edu), Princeton Unversity, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States Ntelekos, A A (ntelekos@princeton.edu), Princeton Unversity, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States Baeck, M (mlbaeck@princeton.edu), Princeton Unversity, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States Yeung, J (jyeung@Princeton.EDU), Princeton Unversity, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States Moshary, F (moshary@ccny.cuny.edu), City College of New York, Department of Electrical Engineering, New York City, NY 10034, United States

Observational and numerical modeling studies are used to examine aerosol – cloud interactions in the New York City metropolitan region. Empirical analyses are based on observations during the period August 2006 – September 2007 from vertically pointing lidar systems operating at 1064, 532 and 355 nm and shadowband radiometers. Observing systems are located in Manhattan and Princeton, NJ and are collocated with ancillary meteorological observing systems. In addition, 3-D reflectivity observations from the KDIX and KOKX WSR-88D radars are used to examine precipitating cloud systems over the region. The objectives of empirical analyses are to characterize temporal and spatial variability of aerosol concentrations over the New York City metropolitan region and to relate variability of aerosol populations to properties of precipitating cloud systems. Empirical analyses are supplemented by numerical modeling studies using the Weather Research and Forecasting (WRF) model with a fully coupled chemistry module, WRF-Chem. Simulation studies are used to examine aerosol impacts on precipitation systems, with special focus on storm systems that passed over the region on 4-5 October 2006 and 16 May 2007. Both empirical and model analyses are also used to guide development of new lidar observing systems incorporating mid-IR sources.

A43C-1435 

Aerosol Optical Properties during GoMACCS and CLASIC: Evidence of Cloud Processing and Scavenging

* Nussbaum, N (nussbaum@lanl.gov), Los Alamos National Laboratory, EES, MS D462, Los Alamos, NM 87545, United States Dubey, M K (dubey@lanl.gov), Los Alamos National Laboratory, EES, MS D462, Los Alamos, NM 87545, United States Mazzoleni, C (claudio@lanl.gov), Los Alamos National Laboratory, EES, MS D462, Los Alamos, NM 87545, United States Gramann, J), Los Alamos National Laboratory, EES, MS D462, Los Alamos, NM 87545, United States Feingold, G (Graham.Feingold@noaa.gov), NOAA ESRL, Chemical Sciences, 325 Broadway, Boulder, CO 80305, United States Schmidt, S), University of Colorado Boulder, LASP, Duane Smith Building, Boulder, CO 80309-0311, United States Hubbe, J), Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, United States Springston, S), Brookhaven National Laboratory, EE, MS 815E, Upton, NY 11973-5000, United States Alexander, L), Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, United States McCubbin, I), University of Nevada, Dept. of Physics/220, Reno, NV 89557, United States Arnott, P), University of Nevada, Dept. of Physics/220, Reno, NV 89557, United States Seinfeld, J), California Institute of Technology, Caltech, 210-41, Pasadena, CA 91125, United States Berkovitz, C), Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, United States

Extensive measurements of aerosol absorption and scattering were performed in the Houston area with the Los Alamos photoacoustic instrument (LAPA) during the GoMACCS campaign in the summer of 2006. The LAPA data are combined with other microphysical data to discern the impacts of clouds on aerosols. A statistical analysis reveals that aerosol scattering and absorption decrease with altitude, consistent with the vertical profiles of condensation particle counts. However, the single scattering albedo (ratio of scattering to total extinction) decreases with altitude above the boundary layer when cloud water increases. This indicates that cloud processing could affect the size of distribution and/or the chemical composition of the aerosols. On particular days we observed long range polluted air at high altitude, which gradually subsided and could be discriminated from the local boundary layer pollution. We examine a variety of correlations between aerosol and cloud properties that would be useful in elucidating the indirect effect. We also analyze the impact of shallow convective cloud fields on aerosol optical properties, both above and below cloud. Finally we report aerosol optical measurements collected in Oklahoma during the CHAPS campaign in the summer of 2007. We apply a similar statistical methodology to differentiate between cloud and clear air observations and report preliminary findings. We detected polluted air masses where both CO and scattering were enhanced in cloud-free air. However, in cloudy air the aerosol scattering was reduced, probably due to scavenging. These results will help us quantify the effects of clouds on aerosols in polluted air masses in the outflow of urban areas. http://aerosols.lanl.gov

A43C-1436 

Vertical Redistribution of Aerosol by Shallow Cumulus Clouds: Observations and Modeling

* Feingold, G (graham.feingold@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Schmidt, K S (sebastian.schmidt@lasp.colorado.edu), University of Colorado, Duane Physics Laboratory for Atmospheric and Space Physics, Boulder, CO 80309, United States Jiang, H (hongli.jiang@noaa.gov), NOAA/CIRA, 325 Broadway, Boulder, CO 80305, United States Jonsson, H (hjonsson@nps.edu), CIRPAS, 3200 Imjin Road, Marina, CA 93933, United States Nussbaum, N (nussbaum@lanl.gov), Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM 87545, United States Mazzoleni, C (claudio@lanl.gov), Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM 87545, United States Dubey, M (dubey@lanl.gov), Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM 87545, United States Murphy, S (shanem@caltech.edu), California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Sorooshian, A (armin@caltech.edu), California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Gates, H (harmony@caltech.edu), California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Flagan, R (flagan@caltech.edu), California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Seinfeld, J (seinfeld@caltech.edu), California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States

The vertical redistribution of aerosol by clouds is a well documented phenomenon for deep convective clouds, but in the case of shallow cumulus, has received little attention. We present observations and modeling of this process based on measurements performed during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) in the summer of 2006. Aerosol properties (total concentration, light scattering and absorption, and composition) were measured on board the CIRPAS Twin Otter. Radiation and surface infrared temperature measurements were used to identify the sections of the highest, above-cloud legs that were influenced by clouds. A comparison is made between the aerosol properties in regions affected by cloud vertical transport, vs. those unaffected by clouds. It is shown that on average there are distinct increases in aerosol concentration and light scattering, as well as changes in composition, in regions above clouds. Large eddy simulations of this convective redistribution indicate increases in aerosol extinction on the order of 15-20%, in broad agreement with the observations.

A43C-1437 

EFFECTS OF AEROSOLS ON TRADE WIND CUMULI OVER THE GULF OF MEXICO: A MODELING AND OBSERVATIONAL STUDY

* Yang, H (hyang31@atmos.uiuc.edu), Department of Atmospheric Sciences, University of Illinois, 105 S.Gregory st., Urbana, IL 61802, United States McFarquhar, G M (mcfarq@atmos.uiuc.edu), Department of Atmospheric Sciences, University of Illinois, 105 S.Gregory st., Urbana, IL 61802, United States Wang, H (Hailong.Wang@noaa.gov), Cooperative Institute for Research in Environmental Sciences (CIRES), NOAA, 325 Broadway, R/CSD3, Boulder, CO 80305, United States Hostetler, C A (Chris.A.Hostetler@nasa.gov), NASA Langley Research Center, National Aeronautics and Space Administration Langley Research Center, Hampton, VA 23681, United States Ferrare, R A (Richard.A.Ferrare@nasa.gov), NASA Langley Research Center, National Aeronautics and Space Administration Langley Research Center, Hampton, VA 23681, United States

The three-dimensional non-hydrostatic Eulerian and semi-Lagrangian (EULAG) anelastic model with warm-rain bulk microphysics was used to investigate how the distribution and physical properties of aerosols affect radiative forcing directly and indirectly over the Gulf of Mexico. Simulations over a 6.4 km by 6.4 km by 3 km domain were initialized with soundings and sea surface temperatures measured on board the Ron Brown research vessel, and with aerosol optical properties retrieved from the High Spectral Resolution Lidar (HSRL) during the Gulf of Mexico Atmospheric Composition and Climate Study(GoMACCS). The vertical profiles of aerosol extinction retrieved from HSRL and Twin Otter flights showed that a Saharan dust layer consisting of non-absorbing aerosols such as ammonium sulfate, dust, seasalt, and nitrate, was overlaid above the cloud layer for several event days. The impact of the Saharan dust layer on cumuli properties was investigated through a series of tests that simulated the diurnal cycle of the cloud field including and excluding the presence of dust on a number of different days. Preliminary results for the 28 August case study show that the dust layer had little impact on the cumuli evolution through its effect on the radiative heating profile. Additional cases will be simulated and presented at the meeting, together with an evaluation of the model results using in-situ and remote sensing data acquired on different days in a variety of meteorological conditions. Comparison will also be made against simulations conducted over the Indian Ocean to further determine how variations in meteorological conditions impact aerosol indirect forcing.

A43C-1438 

Water-Aerosol Interactions Downwind of Mexico City: Inferences about Mixing State, Droplet Growth Kinetics and Aging of Ambient Aerosol

* Lance, S (lance@ucar.edu), Georgia Institute of Technology, EAS Department 311 Ferst Drive, Atlanta, GA 30332-0340, United States Padro, L (luz.padro@chbe.gatech.edu), Georgia Institute of Technology, EAS Department 311 Ferst Drive, Atlanta, GA 30332-0340, United States Sullivan, A (asullivan@eas.gatech.edu), Georgia Institute of Technology, EAS Department 311 Ferst Drive, Atlanta, GA 30332-0340, United States Weber, R (rweber@eas.gatech.edu), Georgia Institute of Technology, EAS Department 311 Ferst Drive, Atlanta, GA 30332-0340, United States Nenes, A (nenes@eas.gatech.edu), Georgia Institute of Technology, EAS Department 311 Ferst Drive, Atlanta, GA 30332-0340, United States Cross, E (eben.cross.1@bc.edu), Aerodyne Research Inc, 45 Manning Road, Billerica, MA 01821-3976, United States Onasch, T (onasch@aerodyne.com), Aerodyne Research Inc, 45 Manning Road, Billerica, MA 01821-3976, United States Worsnop, D (worsnop@aerodyne.com), Aerodyne Research Inc, 45 Manning Road, Billerica, MA 01821-3976, United States Yu, X (Xiaoying.yu@pnl.gov), Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, United States Alexander, L (lizabeth.alexander@pnl.gov), Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, United States Smith, J N (jimsmith@ucar.edu), National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307, United States

We describe observations of size-resolved cloud droplet activation of partially aged Mexico City aerosol obtained during the MIRAGE campaign. These measurements provide unique insight into the integrated chemical properties and mixing state of the aerosol population, in addition to the water uptake kinetics of the particles as they grow into droplets, all of which are crucial constraints for understanding aerosol-cloud-climate interactions and chemical aging of polluted aerosol. A DMT Cloud Condensation Nucleus counter (CCNc) was operated in parallel to a particle counter with an upstream Differential Mobility Analyzer (DMA) to obtain the size-resolved activation fraction for a given water vapor supersaturation (SS). Activation spectra as a function of SS were obtained for the period of March 16-31, 2006. From the activation spectra, we determine the fraction of particles that act as CCN and the mean soluble mole fraction for these particles. We also estimate the variability in soluble mole fraction for these particles by analyzing the slope of the activation spectra, eliminating the effect of particle size variability inherent with the use of a DMA. We then perform "chemical closure" using the Aerosol Mass Spectrometer (AMS) dataset. The AMS data shows a large fraction of organic constituents, which may alter the cloud droplet growth kinetics. We monitor the droplet size distribution at the exit of the CCNc column, and, given the controlled conditions within the CCNc instrument, we can compare the observed droplet growth with the expected growth for classified, pure ammonium sulfate particles of the same critical supersaturation. A numerical model is used to parameterize the droplet growth kinetics in terms of a water vapor uptake coefficient.

A43C-1439 

Assessment of the Relative Importance of Atmospheric Aging on CCN Activity Derived from Field Observations

* Furutani, H (hfurutani@ucsd.edu), University of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093, United States * Furutani, H (hfurutani@ucsd.edu), University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639, Japan Dall'osto, M (mxd266@bham.ac.uk), University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom Roberts, G C (greg@fiji.ucsd.edu), Scripps Institution of Oceanography, 9500 Gilman Dr., La Jolla, CA 92093, United States Prather, K A (kprather@ucsd.edu), University of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093, United States Prather, K A (kprather@ucsd.edu), Scripps Institution of Oceanography, 9500 Gilman Dr., La Jolla, CA 92093, United States

The effect of atmospheric aging on the cloud condensation nuclei (CCN) activity of atmospheric aerosols was studied by comparing different air masses with different degrees of aging along the southern coast of California over the Pacific Ocean during a research cruise on the R/V Roger Revelle from November 2-19, 2004. Activation diameters (D_act) were calculated using the measured CCN concentrations, condensation nuclei (CN) concentrations, and particle size distributions. Measurements of single particle size and chemistry, as well as black carbon (BC) concentrations with an aethalometer, were made to provide further insight into aerosol chemistry. A gradient of aerosol concentrations was encountered: along the coast of California, the highest BC and CN concentrations (1000~6000 ng/m³ and 2000~15000 cm^-3) were measured which decreased as the ship moved away from shore to much lower values (<100 ng/m³, ~300 cm^-3). In all regions, external mixtures of organic carbon, elemental carbon, sea salt, and dust aerosols frequently associated with nitrate and sulfate were observed. A correlation plot between the CCN/CN ratio and D_act exhibits a clear linear correlation, showing a distinct relationship between the extent of anthropogenic aging and CCN activity with the most highly aged air masses showing the highest CCN activity and smallest D_act. These results show changes in aerosol chemistry due to atmospheric aging play an important role in determining the CCN activity of atmospheric aerosols. The present study demonstrates that variations in aerosol chemistry must be taken into account in models to adequately account for the physicochemical properties of atmospheric aerosols and their CCN activity.

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