HR: 08:30h
AN: A41E-03    [Abstracts]
TI: The Impact of Rain Events on Aerosol Optical Properties: Mexico City 2003 and 2006
AU: * Marley, N A
EM: namarley@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue SCLB Room 451, Little Rock, AR 72204-1099, United States
AU: Gaffney, J S
EM: jsgaffney@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue SCLB Room 451, Little Rock, AR 72204-1099, United States
AB: Atmospheric aerosols are now known to play an important role in global climate because of their ability to both scatter and absorb solar radiation, depending on their chemical composition and size. While fine aerosols (0.1- 1.0 microns in diameter) are most effective in scattering shortwave radiation, the dominant light-absorbing aerosol component is carbon soot or black carbon (BC), produced from combustion. The physical removal of large particles (greater than 1 microns) from the atmosphere occurs by gravitational settling while the removal of ultrafine particles (less than 0.1 microns) occurs by diffusion to other aerosol surfaces. This leads to the accumulation of fine aerosols (0.1-1.0 microns) in the atmosphere where the actions of these physical removal mechanisms are at a minimum. These Fine aerosols can adsorb water and grow to a size where gravitationally settling or impaction by falling hydrometeors can occur. Soluble inorganic aerosols are efficiently wet-deposited in this manner, as they are hydrophilic in nature, add water efficiently, and grow rapidly in volume. However, BC aerosols may be more hydrophobic, resisting wet deposition. Thus, the lifetimes of these fine aerosols will depend upon their surface chemistries and hygroscopicity. Measurements of aerosol BC content, light scattering, and absorption were taken in Mexico City during April of 2003 and March of 2006 as part of the Department of Energy's investigations into megacities as major sources of aerosols that would have impacts on regional and global scales. Here we present the results obtained for fine aerosol absorption and scattering in Mexico City during both field efforts. These data are presented as a function of relative humidity and precipitation intensity to determine the effects of wet deposition on the aerosol optical properties. The results indicate that there are substantial amounts of fresh BC aerosols that are not readily washed out during these rain events leading to a decrease in the aerosol single scattering albedo. This work was performed as part of the Department of Energy's Megacity Aerosol Experiment - Mexico City 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-FG02-07ER64329.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly