Wintertime Carbonaceous Aerosols in Los Angeles

Aerosol carbon concentrations have been measured under wintertime conditions at two sites in the Los Angeles basin. Samples were analyzed for total carbon by the Gamma Ray Analysis of Light Elements (GRALE) technique and for elemental carbon by reflectance. Total carbon concentrations at downtown Los Angeles averaged 24 µgm^(-3) and elemental carbon concentrations averaged 9 µgm^(-3) during the 7 am to 1 pm period. The light absorption efficiency of ambient elemental carbon particles was determined to be 11.9 + 0.9 m^2g^(-1), and it was estimated that light absorption by elemental carbon could account for up to 17% of total light extinction in downtown Los Angeles. Baseline conditions for elemental carbon concentrations in the Los Angeles area prior to the introduction of large numbers of diesel passenger cars into the vehicle fleet are established by these measurements. A method for reconstruction of a long time series of past historical air monitoring data on elemental carbon concentrations is described.