Department of Environmental Engineering Science, University of Florida, Gainesville, Florida, USA
Abstract. This study streamlines modeling of the gas–wall process (GWP) of semivolatile organic compounds (SVOC) by predicting gas–wall equilibrium partitioning constant (Kw,i) and accommodation coefficient (αw,i) of SVOC(i) using a quantitative structure–activity relationship. PaDEL-Descriptor, software that calculates molecular descriptors, is employed to obtain physicochemical parameters (i.e., hydrogen bond acidity (Hd,i), hydrogen bond basicity (Ha,i), dipolarity/polarizability (Si), and polarizability (αi)) of SVOC(i). For the prediction of Kw,i, activity coefficients (γw,i) of SVOC(i) to the chamber wall are semiempirically predicted using chamber data in the form of a polynomial equation coupled with the physicochemical parameters. γw,i of various SVOCs differ in functionalities and molecular sizes ranging from 100 to 104. We conclude that the estimation of γw,i is essential to improve the prediction of Kw,i. To predict the impact of relative humidity (RH) on GWP, each coefficient in the polynomial equation for ln(Kw,i) was correlated to RH. Increasing RH enhanced GWP significantly for all polar SVOCs. For example, the predicted Kw,i of 1-heptanoic acid increased more than three times (from 0.58 to 1.96) by increasing RH from 0.4 to 0.75 due to the reduction in γw,i. The characteristic time for GWP are estimated using Kw,i and αw,i to evaluate the effect of GWP on secondary organic aerosol (SOA) mass. It might be significant in the absence of inorganic aerosol, but is insignificant in the presence of electrolytic salts, where aqueous reactions dominate SOA growth.
How to cite. Han, S., Jang, M., and Jiang, H.: Modeling of Gas-Wall Partitioning of Organic Compounds Using a Quantitative Structure–Activity Relationship, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2019-550, 2019.
Received: 07 Jun 2019 – Discussion started: 15 Aug 2019
The gas-wall process (GWP) is the potential source of underestimation in the prediction of the formation of secondary organic aerosol (SOA). In this study, the GWP of semivolatile organic compounds varying in chemical functionalities and volatility was predicted by estimating their GW partitioning constant and accommodation coefficient using a quantitative structure–activity relationship method. The GWP model of this study will improve the model parameters used for SOA predictions.
The gas-wall process (GWP) is the potential source of underestimation in the prediction of the...