Water Uptake of Monoterpene Aerosol Mixtures Produced in an Environmental Chamber

Understanding secondary organic aerosol (SOA) properties is essential in understanding cloud formation, which represents a significant uncertainty in the context of global climate modeling. Monoterpenes and sesquiterpenes are classes of semi-volatile organic compounds (SVOCs), of both biogenic and anthropogenic origins, emitted into the atmosphere. These compounds, when oxidized, contribute to the formation of SOA, resulting in the development of photochemical smog. This represents a significant burden, as it has been found that half of all total fine organic aerosol can be attributed to monoterpene oxidation (Zhang et. al, https://doi.org/10.1073/pnas.1717513115). The resultant aerosol particles may also act as cloud condensation nuclei and contribute to cloud growth. Understanding the water uptake ability, or hygroscopicity, of these compounds improves our knowledge of the radiative effects of smog, which can be used to improve climate models. This study measures the supersaturated droplet growth of fourteen SVOCs throughout controlled exposure to ozone in Bucknell’s environmental chamber through the use of cloud condensation nuclei counting (CCNC). Data from CCNC was collected to produce a single parameter hygroscopicity, or kappa, value for each compound (Petters et. al, https://doi.org/10.5194/acp-7-1961-2007). Given that these components rarely occur in the atmosphere in isolation, an understanding of their group hygroscopicity will prove more valuable than any individual measure. To model this, mixtures of higher quantity components were run, namely 2 and 5 SVOC-component experiments. Included compounds were informed by variation in kappa value observed in individual runs, so as to provide a span of mixture types, from similar (high/high) to contrasting (high/low) in value. While not every possible combination was chosen for experimentation, mixtures were intentionally selected so as to provide a wide base of meaningful data. Preliminary results show that as increasingly many SVOCs are introduced into the reaction mixture, kappa values trend towards a central value, approximately 0.14. This proves promising for further work on increasingly higher component mixtures.