HR: 16:00h
AN: A24B-01    [Abstracts]
TI: Processing of Atmospheric Organic Matter by California Radiation Fogs
AU: * Collett, J L
EM: collett@lamar.colostate.edu
AF: Colorado State University, Atmospheric Science Department, Fort Collins, CO 80523-1371
AU: Youngster, S B
EM: sbyoungs@lamar.colostate.edu
AF: Colorado State University, Atmospheric Science Department, Fort Collins, CO 80523-1371
AU: Lee, T
EM: thlee@lamar.colostate.edu
AF: Colorado State University, Atmospheric Science Department, Fort Collins, CO 80523-1371
AU: Chang, H
EM: huichang@gmail.com
AF: Colorado State University, Atmospheric Science Department, Fort Collins, CO 80523-1371
AU: Herckes, P
EM: Pierre.Herckes@asu.edu
AF: Arizona State University, Department of Chemistry and Biochemistry PO Box 871604, Tempe, AZ 85287-1604
AB: In many environments, organic compounds account for a significant fraction of fine particle mass. Because the lifetimes of accumulation mode aerosol particles are governed largely by interactions with clouds, it is important to understand how organic aerosol particles are processed by clouds and fogs. Recently we have examined the organic composition of radiation fogs in central California as well as how these fogs process organic aerosol particles and soluble organic trace gases. Observations indicate that organic matter is a significant component of the fog droplets, comprising approximately one-third of the total solute mass concentration. Concentrations of total organic carbon (TOC) range from approximately 2 to 41 ppmC. Approximately three-fourths of organic matter is typically found in solution as dissolved organic carbon (DOC). A variety of efforts have been made to characterize the composition of the fog organic matter, including analyses by GC/MS, HPLC, IC, NMR and IR. The most abundant species are typically low molecular weight carboxylic acids, small carbonyls and dicarbonyls, and sugar anhydrides. These species have been observed collectively to account for roughly 20-30 percent of the fog DOC. Dicarboxylic acids, frequently used as model compounds for organic CCN, typically account for only a few percent of the organic carbon, with oxalic acid the most important contributor. A significant portion of the fog DOC appears to be comprised of high molecular weight compounds (> 500 Da). Analyses also reveal the presence of organic molecular markers associated with particles produced by various combustion processes. Comparisons of pre-fog and interstitial aerosol samples reveal differences in the relative particle scavenging efficiencies of the fog drops between organic and elemental carbon and between different types of organic carbon. Measurements using a two-stage fog water collector reveal that organic matter tends to be enriched in smaller fog droplets. Consequently, removal of organic compounds by fog drop deposition is slowed by the lower settling velocities of smaller droplets. Despite this, sedimentation of droplets from long-lived radiation fogs provides an effective mechanism for cleansing the atmosphere of carbonaceous aerosol particles, with deposition velocities of TOC in fogs observed on the order of a few cm/s.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005