Secondary Organic Aerosol Formation from Volatile Chemical Products: Understanding Aerosol Yields and Dynamics

Citation

Charan, Sophia Mohini (2021) Secondary Organic Aerosol Formation from Volatile Chemical Products: Understanding Aerosol Yields and Dynamics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/yvj9-fv16. https://resolver.caltech.edu/CaltechTHESIS:05312021-044610797

Abstract

Particulate matter impacts public health and climate. A major component of small particulate matter, called secondary organic aerosol (SOA), is formed from the condensation of the oxidation products of organic compounds emitted into the atmosphere in the gas phase. Recent analysis suggests that volatile chemical products are responsible for a large fraction of the particulate matter formed from petroleum sources: perhaps more than motor vehicles. This is especially the case in urban areas, which have significant air pollution burdens.

Understanding exactly which precursors are responsible for this large SOA formation and under which conditions is difficult: for each compound, different chemical pathways dominate and even similar molecules can form vastly varied amounts of aerosol. Even if one could study every compound, extrapolating data to the atmosphere is non-trivial. SOA formation is principally understood through laboratory chamber studies, but these studies require a rigorous, quantitative grasp of chamber phenomena to meaningfully interpret the results.

In this dissertation, computational simulations of environmental chambers illuminate the physico-chemical processes that occur within a chamber and the manner in which these processes interact, in order to help extrapolate data to real-world conditions. In particular, the contribution of particle charge to the rate of particle-wall deposition within environmental chambers is investigated.

With this understanding, the amount of aerosol formed per precursor emitted, called the secondary organic aerosol yield, is investigated for benzyl alcohol and decamethylcylopentasiloxane (D5). At atmospherically relevant concentrations, benzyl alcohol and D5 have disparate SOA mass yields: as much as 100% for benzyl alcohol and ~1% for D5. Both of these findings differ from what was previously modeled and measured, indicating the importance of performing experiments on the compounds of interest and evaluating the oxidation products under atmospherically relevant conditions.

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