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

Abstract

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.

Chemical Composition and Hydrolysis of Organic Nitrate Aerosol Formed from Hydroxyl and Nitrate Radical Oxidation of α-pinene and β-pinene

“…The chemical mechanism used in Browne et al (2013) and Zare et al (2018) are based on the Master Chemical Mechanism (MCM) that is well known in the degradation chemistry of VOC in the gas phase (Jenkin et al, 1997;Saunders et al, 2003). However, the same mechanism performs poorly in regards to the chemical composition of SOA (Faxon et al, 2018) as well as the prediction of SOA formation (Ruggeri et al, 2016;Boyd et al, 2017) when equipped with gasparticle partitioning modules based on the absorptive gas-particle partitioning theory (Pankow, 1994). It is, therefore, reasonable to argue that the chemical composition of pON could greatly differ from that of total ON predicted by the MCM.…”

Chemical composition and hydrolysis of organic nitrate aerosol formed from hydroxyl and nitrate radical oxidation of <i>α</i>-pinene and <i>β</i>-pinene

“…Further, ON and HNO 3 can be removed via dry and wet deposition. One important reaction of ON in the particle phase is hydrolysis in the presence of aerosol water, which is a mechanism for NO x loss (Day et al, 2010;Russell et al, 2011). Studies with bulk solutions showed that particlephase hydrolysis of tertiary nitrate is fast with a lifetime of minutes, while primary and secondary nitrate is stable (Darer et al, 2011;Hu et al, 2011).…”

Evaluating the mutagenic potential of aerosol organic compounds using informatics-based screening

“…No experimental data are available for the ambient concentrations of organic compounds belonging to Clusters 7 or 8. However, SOA modelling studies indicate that they can account for a significant fraction of SOA mass formed by substituted benzene oxidation (Ruggeri et al, 2016), which translates into ambient concentrations of several ng m −3 in very polluted environments (such as in Yuan et al, 2013; Table S10). The formation of endoperoxides and epoxides and of other reactive oxygenated organic compounds, such as those in Clusters 7 and 8, was hypothesized by Fu et al (2012) to explain the DNA damage caused by photodegraded aromatic compounds.…”