THESIS
2013
xxiii, 253 p. : ill. (some col.) ; 30 cm
Abstract
Aerosols are complex mixtures of inorganic and organic constituents that exert
pronounced effects in global climate, regional visibility and human health. Currently,
atmospheric models have greatly underestimated the burden of secondary organic
aerosols (SOA) partly because of inadequate understanding of the partitioning and
heterogeneous reactions of organic species. This work employed a tailor-made Raman
spectroscopy system coupled with an electrodynamic balance (EDB) to examine
various physical and chemical uptake processes of organic vapors relevant to SOA
formation. The masses, chemical compositions and phase states of particles under
investigation were simultaneously monitored for an extended period of time (~24 hours)
to capture the crucial processes that result in new m...[
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Aerosols are complex mixtures of inorganic and organic constituents that exert
pronounced effects in global climate, regional visibility and human health. Currently,
atmospheric models have greatly underestimated the burden of secondary organic
aerosols (SOA) partly because of inadequate understanding of the partitioning and
heterogeneous reactions of organic species. This work employed a tailor-made Raman
spectroscopy system coupled with an electrodynamic balance (EDB) to examine
various physical and chemical uptake processes of organic vapors relevant to SOA
formation. The masses, chemical compositions and phase states of particles under
investigation were simultaneously monitored for an extended period of time (~24 hours)
to capture the crucial processes that result in new mass formation. The measured
partition coefficients (K
p) of alcohols in oleic acid droplets matched with the Pankow’s
absorptive partitioning model and verified the technique. Further, the roles of particle
chemical nature and phase states in the heterogeneous reactive uptake were extensively investigated. Particles of sulfuric acid and their mixtures with hydrophobic
(oleic acid) or hydrophilic (levoglucosan) organics were allowed to react with nonanal
vapor. The initial uptake coefficient of oleic acid/sulfuric acid mixture was much larger
than that of pure sulfuric acid showing that the presence of hydrophobic organic
materials in particles enhanced the reactive uptake of nonanal. The ozonolysis of maleic
acid and the displacement of ammonium by amines in aqueous droplets or in crystalline
solids were investigated. The compact solids suffered from substantial mass transfer
limitation and the reaction rates were remarkably lower than those of aqueous droplets.
The results of the active displacement of ammonium in aqueous particles by various
short-chain amines may be related to the field-observed aminium ions in samples during
high humidity or fog/rain events.
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