Formation of Secondary Organic Aerosols in Atmospheric Liquid Wate

The formation of secondary organic aerosols through aqueous processes (aqSOA) has been identified as an important route in forming organic aerosols; however, many aspects of this formation are still uncertain. One main uncertainty is the nature by which these aqueous compounds are formed, whether the formation is reversible, irreversible, or a mixture of both. To date, there are no ambient measurements to quantify or constrain the relative contributions of reversible/irreversible aqSOA. Hence, we have developed an online method to simultaneously measure water-soluble organic carbon in the gas (WSOCg) and particle (WSOC p) phases to characterize the reversible and irreversible uptake of water-soluble organic gases to aerosol liquid water (ALW) across the different seasons in Maryland located in the eastern United States.;The formation of aqSOA was observed in all four seasons during the night, and was predominantly associated with the availability of ALW. In the fall and winter, there was no statistically significant difference in WSOC p concentrations through the dry and ambient channels, suggesting irreversible aqSOA formation. However, there was a systematic difference between ambient and dry WSOCp measurements in the late spring and summer, indicating reversible aqSOA formation. Conditions that promote reversible aqSOA formation were clearly present starting from the late spring and into the summer, but were not significant during the winter and the fall. During the late spring and summer, aqSOA formation was tightly linked with isoprene oxidation, while the aqSOA formed in the winter was associated with biomass burning due to residential heating. The quantity of evaporated WSOCp was strongly related to relative humidity, WSOCp concentrations, and NO x/isoprene ratios. The split between reversible and irreversible aqSOA formation was related to NOx, suggesting that low-NOx isoprene oxidation products were responsible for the reversible aqSOA. Given the diverse climatology and aerosol sources that impact Baltimore, it is likely that this phenomenon occurs in many other locations. The results presented in this thesis have several important implications for atmospheric chemistry, atmospheric modeling, several atmospheric measurement methods, and regulations and health.