Articles | Volume 16, issue 14
Research article
18 Jul 2016
Research article |  | 18 Jul 2016

Model–measurement comparison of functional group abundance in α-pinene and 1,3,5-trimethylbenzene secondary organic aerosol formation

Giulia Ruggeri, Fabian A. Bernhard, Barron H. Henderson, and Satoshi Takahama

Abstract. Secondary organic aerosol (SOA) formed by α-pinene and 1,3,5-trimethylbenzene photooxidation under different NOx regimes is simulated using the Master Chemical Mechanism v3.2 (MCM) coupled with an absorptive gas–particle partitioning module. Vapor pressures for individual compounds are estimated with the SIMPOL.1 group contribution model for determining apportionment of reaction products to each phase. We apply chemoinformatic tools to harvest functional group (FG) composition from the simulations and estimate their contributions to the overall oxygen to carbon ratio. Furthermore, we compare FG abundances in simulated SOA to measurements of FGs reported in previous chamber studies using Fourier transform infrared spectroscopy. These simulations qualitatively capture the dynamics of FG composition of SOA formed from both α-pinene and 1,3,5-trimethylbenzene in low-NOx conditions, especially in the first hours after start of photooxidation. Higher discrepancies are found after several hours of simulation; the nature of these discrepancies indicates sources of uncertainty or types of reactions in the condensed or gas phase missing from current model implementation. Higher discrepancies are found in the case of α-pinene photooxidation under different NOx concentration regimes, which are reasoned through the domination by a few polyfunctional compounds that disproportionately impact the simulated FG abundance in the aerosol phase. This manuscript illustrates the usefulness of FG analysis to complement existing methods for model–measurement evaluation.

Short summary
Functional groups provide an intermediate level of chemical resolution between full molecular speciation and elemental composition for describing complex mixtures and can be a useful metric in model–measurement comparison of reaction kinetics and secondary organic aerosol formation. We introduce tools to facilitate such comparisons and demonstrate its application in study of the photooxidation of two precursor volatile organic compounds and the gas–particle partitioning of their products.
Final-revised paper