Secondary organic aerosol (SOA) forms via a complex interaction of sunlight, humidity, hydrocarbons from vegetation, vehicles, and industrial emissions, and other airborne chemicals. SOA formation is also influenced by heterogeneous chemistry on preexisting particulate matter, such as sulfated inorganic aerosol, sea salt, and airborne mineral dust. Many studies found aerosol chemistry in sulfated inorganic aerosol to be sensitive to liquid water content (LWC) and acidity. There are a few recent SOA models that include aqueous reactions, however, current SOA models are limited. While models incorporate aerosol phase reactions of several products that are considered to be significant in SOA formation (e.g., glyoxal and IEPOX), they poorly incorporate the multiphase heterogeneous chemistry of many other organic species into SOA formation. Our laboratory’s efforts have improved the state-of-the-art science via the development of the UNIPAR model, which utilizes explicit gas mechanisms to predict SOA formation from multiphase reactions (gas, organic, and aqueous phases). In conjunction of gaseous products with the estimation of organic concentration, SOA models faces the challenge in the prediction of the solubility (activity coefficient) of organics in highly salted aqueous aerosol using the thermodynamic model (i.e., AIOMFAC), which requires demanding computations for interaction energies in a multicomponent system under dynamically environments. In UNIAPR, solubility of gaseous organics in salted aqueous meida is predicted with self-contained polynomial equations via the correlation between AIOMFAC outputs and the parameters associated with the structure of organics (molecular weight and oxygen to carbon ratio) and aerosol media (org/sulfate ratio and fractional sulfate in inorganic composition) over the series of LWC linked to different humidity. The resulting activity coefficients are applied to prediction of SOA growth via gas-particle partitioning and heterogeneous reactions (oligomerization in organic phase and aqueous phase) of all known organic species under broad ranges of aerosol acidity and humidity to form both the dry and the wet inorganic salted aerosols. SOA growth via heterogeneous chemistry in aqueous media is not limited to sulfated aerosol. We observed the dramatic effect of sea salt aerosol on SOA growth. We also found suppression of SOA growth by hygroscopicity of mineral dust, which has the catalytic ability to form oxidants.

Organic aerosol growth via aqueious reactions in the presence of different inorganic aerosols containing ammonium sulfate, sea salt, and airborne mineral dust

2019 Fall National Meeting

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