NON-FOSSIL-FUEL FINE-PARTICLE ORGANIC-CARBON AEROSOLS IN SOUTHERN CALIFORNIA DETERMINED DURING THE LOS-ANGELES AEROSOL CHARACTERIZATION AND SOURCE APPORTIONMENT STUDY

The urban Southern California atmospheric fine-particle (d(p) < 3.5 mu m) aerosol burden is composed of a mixture of organic, inorganic, and ''black'' carbon particles. It has been estimated that this fraction contains as an average 25% total carbon, which is equal to approximately 45% organic material. Identification by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was able to account for approximately 46% of the extractable organic material. The dominant families identified and quantified in the extractable organic matter are; aromatic acids (18.2%), hydrocarbons (13.8%), ketones (8.2%), aliphatic acids (8.1%), nitro compounds (7.8%, esters (4.6%), and unidentified (39.3%). Total filter extracts, as well as fractionated extracts and nonextractable (''black'' carbon?) were analyzed for C-14/(1)2C and C-13/C-12 isotope ratios to determine the relative content of modern carbon in the aerosols, collected by high-vol samplers. From the SCAQS program conducted in 1987, a range of C-14 measurements were obtained for modern carbon extending from 17% to 63% modern carbon. The lowest average carbon content was measured in downtown Los Angeles (27% and the highest average modern carbon was found in Rubidoux (54%), with an annual average for all sites of 38.8%. Fractionated samples showed that the hydrocarbon fraction contains the lowest content of modern carbon (1-3%), whereas the polar fraction contains 22%-44% modern carbon and the ''black'' residual carbon contains 16%-30% modern carbon. In a similar investigation conducted in 1986 as part of the Carbonaceous Species Methods Comparison Study (CSMCS), high vol samplers were deployed in Glendora, Duarte and later (1990) at the Caldecott Tunnel (Berkeley). The average modern carbon in the hydrocarbon, polar and elemental carbon fractions for Glendora and Duarte are approximately 15%, 27%, and 32%, respectively, whereas for Caldecott Tunnel it is 0%, 9.5%, and 9%. Both the above studies were part of the LA-ACSAS supported by Southern California Edison Company. These data demonstrate that aerosol from urban areas can contain significant amounts of nonfossil fuel contemporary carbon.