QUANTIFICATION OF URBAN ORGANIC AEROSOLS AT A MOLECULAR-LEVEL - IDENTIFICATION, ABUNDANCE AND SEASONAL-VARIATION

Organic aerosol samples collected systematically throughout a complete annual cycle at four urban sites in southern California are examined by high-resolution ps chromatography and gas chromatography/mass spect rometry. More than 80 organic compounds are quantified and their seaso nal ambient concentration patterns are discussed. Primary organic aero sol constituents are readily identified, revealing an annual pattern, with high winter and low summer concentrations. In contrast, aliphatic dicarboxylic acids of possible secondary origin show a reverse patter n, with high concentrations in late spring/early summer. Concentration patterns similar to the secondary dicarboxylic acids also are found f or aromatic polycarboxylic acids, certain lower molecular weight n-alk anoic acids, nonanal and other compounds. Molecular markers characteri stic of woodsmoke are identified, and their concentrations change by s eason in close agreement with prior estimates of the seasonal use of w ood as a fuel. This data set can be used to evaluate the predictions o f mathematical models for the atmospheric transport and reaction of or ganic aerosol constituents defined at a molecular level.