The formation, properties and impact of secondary organic aerosol: current and emerging issues
Secondary organic aerosol (SOA) accounts for a significant fraction\nof ambient tropospheric aerosol and a detailed knowledge of the formation,\nproperties and transformation of SOA is therefore required to evaluate\nits impact on atmospheric processes, climate and human health. The\nchemical and physical processes associated with SOA formation are\ncomplex and varied, and, despite considerable progress in recent\nyears, a quantitative and predictive understanding of SOA formation\ndoes not exist and therefore represents a major research challenge\nin atmospheric science. This review begins with an update on the\ncurrent state of knowledge on the global SOA budget and is followed\nby an overview of the atmospheric degradation mechanisms for SOA\nprecursors, gas-particle partitioning theory and the analytical techniques\nused to determine the chemical composition of SOA. A survey of recent\nlaboratory, field and modeling studies is also presented. The following\ntopical and emerging issues are highlighted and discussed in detail:\nmolecular characterization of biogenic SOA constituents, condensed\nphase reactions and oligomerization, the interaction of atmospheric\norganic components with sulfuric acid, the chemical and photochemical\nprocessing of organics in the atmospheric aqueous phase, aerosol\nformation from real plant emissions, interaction of atmospheric organic\ncomponents with water, thermodynamics and mixtures in atmospheric\nmodels. Finally, the major challenges ahead in laboratory, field\nand modeling studies of SOA are discussed and recommendations for\nfuture research directions are proposed.