Impacts of phase state and water content on secondary organic aerosol formation and partitioning
Authors
Manabu Shiraiwa — University of California, Irvine
Annmarie G Carlton — University of California, Irvine
James Smith — University of California, Irvine
Sergey Nizkorodov — University of California, Irvine
Alexander Laskin — Purdue University
Allen Goldstein — University of California, Berkeley
Category
Secondary organic aerosol
Description
Secondary organic aerosols (SOA) can occur in amorphous solid or semi-solid phase states depending on chemical composition, relative humidity (RH), and temperature. The phase transition between amorphous solid and semi-solid states occurs at the glass transition temperature (Tg). We developed a method to estimate Tg of pure compounds containing carbon, hydrogen, and oxygen atoms (CHO compounds) with molar mass up to ~1100 g mol-1 using the number of carbon, hydrogen, and oxygen atoms. Viscosity can be predicted from the Tg-scaled Arrhenius plot of fragility (viscosity vs. Tg/T) as a function of the fragility parameter D. We compiled D values of organic compounds from literature, and found that D approaches a lower limit of ~10 as the molar mass increases. Viscosity of α-pinene and isoprene SOA was estimated as a function of RH by accounting for hygroscopic growth of SOA and applying the Gordon-Taylor mixing rule, reproducing previously published experimental measurements very well. Sensitivity studies were conducted to evaluate impacts of Tg, D, hygroscopicity parameter (κ), and the Gordon-Taylor constant on viscosity predictions. Viscosity of toluene SOA was predicted using the elemental composition obtained by high-resolution mass spectrometry (HRMS), resulting in a good agreement with the measured viscosity. We also estimated viscosity of biomass burning particles using the chemical composition measured by HRMS with two different ionization techniques: electrospray ionization (ESI) and atmospheric pressure photoionization (APPI). We analyze gas-particle partitioning of SOA oxidation products (i.e., pinonic acid, pinic acid, methyl tetrols), as measured by semi-volatile thermal desorption aerosol gas chromatography (SV-TAG) during the GoAmazon2014/15 campaign. Our analysis aims at quantifying kinetic limitations of diffusive transport for uptake of organic compounds by applying a kinetic multi-layer model. We work also on developing a model representation and evaluating the effects of phase state and water content on SOA evaluation in a regional air quality model and to compare model predictions with field measurements.
