The water uptake characteristics of an atmospheric aerosol particle is among the properties controlled by chemical composition, which is relevant for particle size and radiation interactions. Modeling the equilibrium water content of a particle involves predicting the gas–particle partitioning of water at a certain relative humidity (RH) and temperature. Furthermore, the equilibration is affected by non-ideal mixing in liquid phases and the simultaneous partitioning of semivolatile organic and inorganic species. Thermodynamic and dynamic models of these processes attempt to provide accurate predictions for use in process-level and large-scale atmospheric models. However, considerations of higher chemical complexity and the physical chemistry of gas–particle interactions come with an increase in computational costs. Features like liquid–liquid phase separation and RH-dependent particle morphology have gained interest due to their impact on multiphase chemistry, hygroscopicity, the viscosity of particle phases, predicted aerosol mass concentrations, and aerosol–cloud effects. Case studies suggest that the interplay of aerosol hygroscopicity at elevated RH and the partitioning of other semivolatile species affect overall particle mass concentrations, particle surface composition and the cloud formation potential of ultrafine particles. Meanwhile, model frameworks to capture the multiphase and multicomponent nature of atmospheric aerosols have been introduced primarily for detailed process studies. Treatments of such features within large-scale atmospheric models will benefit from a reduced-complexity approach.<br/>In this presentation, we will introduce a reduced-complexity organic aerosol model that accounts for water content. Our reduced-complexity model is based on the detailed AIOMFAC model. While equilibrium framework based on AIOMFAC allows accounting for organic–inorganic interactions in liquid phases when chemical structure information is available, the advantage of the reduced-complexity model lies in using only input typically available from field measurements or the data represented in large-scale air quality models. Our approach is compatible with a volatility basis set approach and allows for extending it by adding a realistic humidity dependence. In addition, we propose a pathway to account for phase separation effects in a simplified manner. This approach and its results for aerosol hygroscopicity and cloud droplet activation will be discussed.

Modeling water uptake and cloud droplet formation potential of multiphase aerosols

2019 Fall National Meeting

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