Master of Science in Chemical Engineering (MSChE)
Fog is a multiphase dynamic system which can provide a setting for various physicochemical processes affecting the fate of various organic pollutants such as polycyclic aromatic hydrocarbons (PAH) and their oxygenated forms (oxy-PAH) in the atmosphere. This study focuses on the processing of PAH and oxy-PAH during a smog-fog-smog cycle. Two field campaigns were carried out during the winters of year 2010 and year 2011 in the Central Valley of California, sampling two fog events in Fresno and five fog events in Davis. To study the transformations and distributions of PAH and oxy-PAH, different atmospheric species (fog water, gas phase, and particulate matter) were sampled. All the samples were extracted with dichloromethane and were analyzed in a gas chromatograph coupled to a mass spectrometric detector in a single-ion monitoring mode. The pre- and post-fog PM2.5 samples showed a significant increase in the concentrations of most of the oxy-PAH after the fog events, suggesting the formation of oxy-PAH during a fog event. The PM2.5 samples collected continuously during a fog event showed a gradual decrease in the concentrations of all the compounds indicating their influx to water. The analysis of fog water samples and the particulate matter separated from them consistently displayed high concentrations of oxy-PAH in fog water samples and high concentrations of PAH in fog water particulate matter samples, indicating the possible formation of oxy-PAH in fog water by the oxidation of PAH and also their dissolution into the fog water. Fog water samples also revealed that as the fog formation starts the compounds are taken up by the particle phase and are dissolved in the surrounding water. The PAH can oxidize to oxy-PAH by a rate-limiting oxidation process acting on the particulate matter itself and the products can get further dissolved in the fog water. The PAH present in the fog water can get converted to oxy-PAH in the fog water. Also, as the fog starts to dissipate the water in aquasols starts to evaporate from the top, which makes the remaining fog water and the particulate matter more concentrated with these compounds.
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Khadapkar, Kalindi Pramod, "A study of a smog-fog-smog cycle and the processing of PAH and oxy-PAH by a fog cloud" (2011). LSU Master's Theses. 2937.
Valsaraj, Kalliat T.