Final Technical Report: DE-FG03-01ER63099/DE-FG02-01ER63099

Organic material contributes {approx}20-50% to the total fine aerosol mass at continental mid-latitudes (Saxena and Hildemann, 1996; Murphy et al., 1998; Peterson and Tyler, 2002; Putaud et al., 2004) and as much as 90% in tropical forested areas (Andreae and Crutzen, 1997; Artaxo et al., 2002). Significant amounts of carbonaceous aerosols are also observed in the free troposphere (Heald et al., 2005). A substantial fraction of the organic component of atmospheric particles consists of water-soluble, possibly multifunctional compounds (Saxena and Hildemann, 1996; Kavouras et al., 1998). It is critical that we understand how organic aerosols and their precursors are transformed in the atmosphere and the dependence of the transformation on the chemical and thermodynamic conditions of the ambient environment: (1) to accurately forecast how changing emissions will impact atmospheric organic aerosol concentrations and properties on the regional to global scale, and (2) to relate atmospheric measurements to sources. A large (but as yet unquantified) fraction of organic aerosol is formed in the atmosphere by precursor gases. In addition, both primary and secondary organic aerosol interact with other gas and aerosol species in the atmosphere so that their properties (i.e., size, hygroscopicity, light absorption and scattering sphere efficiency) can change significantly with time and distance from their source. Organic aerosols (OA) are composed of complex mixtures of different organic species from less-polar organics (n-alkanes, polycyclic aromatic hydrocarbons, fatty alcohols, fatty acids, etc.) to highly polar organics such as dicarboxylic acids and multi-functional organic acids. Studies employing FTIR spectroscopy and NEXAFS have demonstrated the presence of different functional groups such as ketonic and carboxylic groups. Humic-like substances (HULIS) have been identified in aerosols. Field observation and laboratory smog chamber studies have demonstrated that oxidative reactions of biogenic and anthropogenic precursors in the gas phase produce low molecular weight organic acids such as oxalic and other dicarboxylic acids, dicarbonyls and multi-functional organics. Oxidation reactions in the particle phase may also produce oxygenated species, including aldehydes, organic acids, and large molecules such as HULIS. Despite this progress, a significant fraction of atmospheric OA still remains poorly characterized