Modeling of Gas-Wall Partitioning of Organic Compounds Using a Quantitative Structure–Activity Relationship

Abstract

<p><strong>Abstract.</strong> This study streamlines modeling of the gas–wall process (GWP) of semivolatile organic compounds (SVOC) by predicting gas–wall equilibrium partitioning constant (<i>K<sub>w,i</sub></i>) and accommodation coefficient (<i>α<sub>w,i</sub></i>) of SVOC(<i>i</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 (<i>H<sub>d,i</sub></i>), hydrogen bond basicity (<i>H<sub>a,i</sub></i>), dipolarity/polarizability (<i>S<sub>i</sub></i>), and polarizability (<i>α<sub>i</sub></i>)) of SVOC(<i>i</i>). For the prediction of <i>K<sub>w,i</sub></i>, activity coefficients (<i>γ<sub>w,i</sub></i>) of SVOC(<i>i</i>) to the chamber wall are semiempirically predicted using chamber data in the form of a polynomial equation coupled with the physicochemical parameters. <i>γ<sub>w,i</sub></i> of various SVOCs differ in functionalities and molecular sizes ranging from 100 to 104. We conclude that the estimation of <i>γ<sub>w,i</sub></i> is essential to improve the prediction of <i>K<sub>w,i</sub></i>. To predict the impact of relative humidity (RH) on GWP, each coefficient in the polynomial equation for ln(<i>K<sub>w,i</sub></i>) was correlated to RH. Increasing RH enhanced GWP significantly for all polar SVOCs. For example, the predicted <i>K<sub>w,i</sub></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 <i>γ<sub>w,i</sub></i>. The characteristic time for GWP are estimated using <i>K<sub>w,i</sub></i> and <i>α<sub>w,i</sub></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.</p>

Modeling the Influence of Chain Length on SOA Formation via Multiphase Reactions of Alkanes

“…In addition to wall loss of precursor HC, intermediate oxidized products derived from the precursor HC can deposit to the wall. The organic vapor deposition to wall is kinetically described with the deposition (kon,i) and desorption (koff,i) rate constants of each lumping species, i, to the UF-APHOR wall by using the method detailed by Han et al (2019). kon,i is expressed as a fractional loss rate (Mcmurry and Grosjean, 1985):…”

“…The values of Hd,i, Ha,i, and 𝛼i (Table S2) were calculated using the PaDEL-Descriptor, (Yap, 2011). The value of Kw,i is used along with the kon,i to predict intermediate product using an analytical equation from the study by Han et al (2019)…”