Anthropogenic Influence On The Fate Of Secondary Organic Aerosol

Oxidation of volatile organic compounds (VOC) in the atmosphere leads to the formation of secondary organic aerosol (SOA), which can have extensive impacts on air quality, health, and climate. Existing air quality models used to describe the fate of ambient organic aerosol tend to underpredict the aerosol oxidation state. In addition, modeled concentrations of nitrogen oxides (NO [subscript x]) and other reactive nitrogen compounds (NO [subscript y]), including alkyl nitrates, often deviate from field observations. Certain SOA formation pathways, SOA ageing mechanisms, and alkyl nitrate decay mechanisms may be missing. Recent field studies show that NO [subscript x]-mediated heterogeneous production of nitryl chloride, ClNO2, could provide a ubiquitous source for chlorine atoms. Little is known about the role of chlorine atoms in SOA formation and ageing, or their interaction with other anthropogenic emissions found in polluted environments, where alkane oxidation chemistry is important. Environmental chamber experiments are carried out to address knowledge gaps in atmospheric chlorine and alkane oxidation chemistry. Results show that chlorine-initiated oxidation of isoprene leads to SOA formation, organic chloride formation, and possibly secondary HO [subscript x] chemistry. Alkane-derived alkyl nitrate compounds are found not to hydrolyze appreciably in humid environments or in the presence of acidic aerosol. Uptake of inorganic nitrate and inorganic chloride are observed in the presence of deliquescent particles. Chlorine-initiated oxidation of linear alkanes is shown to result in prompt SOA formation and delayed organic chloride formation, which is enabled by the addition of chlorine radical to dihydrofuran, a heterogeneously produced multi-generational oxidation product. Improvements are made for the detection of organic chloride using aerosol mass spectrometry, and for aerosol volatility measurements using temperature programmed thermal desorption techniques. A two-dimensional thermogram framework is developed to visualize aerosol composition, aerosol volatility, and thermal fragmentation simultaneously