Secondary organic aerosols (SOA) make up a substantial fraction of the fine particulate mass in the lower troposphere, and large uncertainties still exist in their abundance, sources and evolution in the atmosphere. A major focus of the current environmental chamber studies is on the SOA formation from the gas-phase oxidation of individual volatile organic precursors. The observation that organosulfates present even in neutralized ammonium sulfate aerosols suggests that interactions between the organic and the condensed neutralized inorganic materials are complicated and poorly understood. Though sulfate is often used as a proxy for the inorganic components in laboratory studies, the decrease of the global sulfate level will make nitrate a more important driver of climate effects and...[ Read more ]

Secondary organic aerosols (SOA) make up a substantial fraction of the fine particulate mass in the lower troposphere, and large uncertainties still exist in their abundance, sources and evolution in the atmosphere. A major focus of the current environmental chamber studies is on the SOA formation from the gas-phase oxidation of individual volatile organic precursors. The observation that organosulfates present even in neutralized ammonium sulfate aerosols suggests that interactions between the organic and the condensed neutralized inorganic materials are complicated and poorly understood. Though sulfate is often used as a proxy for the inorganic components in laboratory studies, the decrease of the global sulfate level will make nitrate a more important driver of climate effects and poor air quality in coming decades. Ambient particulate nitrate concentration has been increasing continuously in recent years especially in the mega cities because of the increase in the emission of their precursors and ammonia. Field and laboratory studies of interactions between the inorganic and organic components on SOA formation are in great need. Further, recent laboratory chamber studies have reported increasing SOA mass corresponding to increasing initial seed surface area, suggesting that organic vapor wall loss significantly suppresses the SOA yield measured in the chamber. Yet its impacts on the properties of SOA remain unknown.

This thesis presents results from a field study in Hong Kong, in which the abundance of organic sulfur compounds was estimated in real-time using an Aerodyne high-resolution aerosol mass spectrometer. Further, the parameters that potentially affect their formation, such as sulfate abundance, particle-phase water, particle acidity, meteorology etc., were examined. Chamber experiments of SOA formation from α-pinene ozonolysis with the presence of nitrate or sulfate seed particles at different seed levels were conducted to investigate the effects of level and type of inorganic seed aerosols on the chemical properties of SOA.