The influence of environmental parameters on secondary organic aerosol (SOA) was extensively investigated in the UC Riverside/CE-CERT environmental chamber. The presence of water vapor provided an additional SOA formation pathway during cyclohexene ozonolysis that increased SOA formation by ∼30%. The presence of dissolved salts had minimal impact as compared to the presence of water vapor. Temperature proved to be an important SOA formation parameter; aerosol formation increased by 3.5 times at 278K as compared to 300K for both α-pinene and cyclohexene isothermal ozonolysis. Changing experimental temperatures, in most cases led to a different gas-particle equilibrium, even after returning to the original temperature set point. A model, temperature influenced partitioning aerosol yield (TIPAY), was created to explain these results by incorporating a thermally labile component, a traditional gas to particle partitioning component, and an additional gas to particle partitioning component whose formation potential was temperature independent. Increasing light intensity, measured as the photolysis rate of NO2 to NO (k1), was found to increase SOA formation for the m-xylene/NOx photooxidation system. Irradiation source had a slight effect on total SOA formation as an irradiation spectrum more similar to natural light produced slightly more SOA than that with black lights, provides the wavelengths necessary for NO2 photolysis, at the same light intensity. Modeling of the gas phase chemistry with SAPRC07, supports the idea that the concentration of radical species OH and HO 2 greatly determine the amount of SOA formation. Building on SAPRC07, the SOA formation model PM-SAPRC08, was developed to determine the dominate gas phase reactions needed to predict SOA formation results for 100 experiments. While 7 simulations are tested, several of which are published routes, none adequately predicted SOA formation. Results of the influence of these environmental parameters provide a wealth of experimental data, along with model simulations that provide insight to SOA formation behavior and SOA formation mechanisms; essential to bridging the apparent disconnect between models of SOA production based on environmental chambers and that estimated from direct ambient measurements.
|Advisor:||Cocker, David R., III|
|School:||University of California, Riverside|
|School Location:||United States -- California|
|Source:||DAI-B 69/06, Dissertation Abstracts International|
|Subjects:||Atmosphere, Environmental science, Environmental engineering|
|Keywords:||Aromatics, Environmental chamber, PM-SAPRC08, Photooxidation, Secondary organic aerosols|
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