Formation of Secondary Organic Aerosols

	Caltech smog chamber

Secondary organic aerosol (SOA), formed in the atmospheric oxidation of gas-phase organic compounds and subsequent gas-particle partitioning of lower-volatility reaction products, is a major contributor to the total tropospheric particulate burden. As a result, the need for an accurate understanding of atmospheric aerosols and their effects requires that models of gas-phase atmospheric chemistry include processes governing the formation and fate of SOA. Because the chemistry of SOA formation is complex, laboratory chamber studies of SOA formation and growth serve as the basis for developing that understanding. The Caltech chamber laboratory has been the source of much of the world’s data on the formation of SOA from parent hydrocarbons. Current studies are aimed at understanding the role of gas-phase chemistry in SOA formation and defining the entire suite of the most important hydrocarbon precursors to ambient organic aerosol.

Recent studies include:

• SOA formation from isoprene under high- and low-NO_x conditions; SOA formation from isoprene + NO₃ radical
• SOA formation from aromatic hydrocarbons: m-xylene, toluene and benzene
• NO_x dependence of SOA formation from photooxidation of biogenic hydrocarbons
• Formation of sulfate esters in SOA from isoprene and monoterpenes
• SOA formation from aliphatic amines