A predictive model for secondary organic aerosol (SOA) formation including both partitioning and heterogeneous reactions is explored for the SOA produced from the oxidation of toluene in the presence of inorganic seed aerosols. The predictive SOA model comprises the explicit gas-phase chemistry of toluene, gas-particle partitioning, and heterogeneous chemistry. The resulting products from the explicit gas phase chemistry are lumped into several classes of chemical species based on their vapor pressure and reactivity for heterogeneous reactions'. Both the gas-particle partitioning coefficient and the heterogeneous reaction rate constant of each lumped gas-phase product are theoretically determined using group contribution and molecular structure-reactivity. in the SOA model, the predictive SOA mass is decoupled into partitioning (OMP) and heterogeneous aerosol production (OMH). OMP is estimated from the SOA partitioning model developed by Schell et al. (J. Geophys. Res. 2001, 106, 28275-28293) that has been used in a regional air quality model (CMAQ 4.7). OMH is predicted from the heterogeneous SOA model developed by Jang et al. (Environ. Sci. Technol. 2006, 40, 3013-3022). The SOA model is evaluated using a number of the experimental SOA data that are generated in a 2 m(3) indoor Teflon film chamber under various experimental conditions (e.g., humidity, inorganic seed compositions, NOx concentrations). The SOA model reasonably predicts not only the gas-phase chemistry, such as the ozone formation, the conversion of NO to NO2, and the toluene decay, but also the SOA production. The model predicted that the OMH fraction of the total toluene SOA mass increases as NOx concentrations decrease: 0.73-0.83 at low NOx levels and 017-0.47 at middle and high NOx levels for SOA experiments with high initial toluene concentrations. Our study also finds a significant increase in the OMH mass fraction in the SOA generated with low initial toluene concentrations, compared to those with high initial toluene concentrations. On average, more than a 1-fold increase in OMH fraction is observed when the comparison is made between SOA experiments with 40 ppb toluene to those with 630 ppb toluene. Such an observation implies that heterogeneous reactions of the second-generation products of toluene oxidation can contribute considerably to the total SOA mass under atmospheric relevant conditions.
Aerosol-particles; Air-quality-measurement; Chemical-reactions; Environmental-exposure; Exposure-assessment; Exposure-levels; Exposure-methods; Gases; Inorganic-compounds; Molecular-structure; Organic-chemicals; Organic-vapors; Particle-aerodynamics; Particulate-dust; Particulates; Statistical-analysis
Myoseon Jang, Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, Fl 32611