Functional group distribution of secondary organic aerosol generated using the Master Chemical Mechanism: similarities and discrepancies with environmental controlled chamber studies

In this work, composition of organic aerosol simulated by the Master Chemical Mechanism coupled with a dynamic absorptive partitioning model is compared against infrared spectroscopy measurements of functional group abundance in chamber experiments. The Master Chemical Mechanism (MCM, Jenkin et al., 1997; Saunders et al., 2003; Jenkin et al., 2003; Bloss et al., 2005) is a near-explicit gas phase chemistry model that describes the degradation of various emitted volatile organic compounds. SIMPOL.1, a group contribution model (Pankow and Asher, 2008), was used to calculate pure components vapour pressures of the degradation products. Fourier transform infrared spectroscopy (FTIR) is able to quantify the vibrational absorption of molecular bonds (Maria et al., 2002) and is used to study aerosol functional group composition to have information on the sources and processes involved in aerosol formation and aging (Russell et al., 2011). MCM has been used to study aerosol atomic composition in terms of O:C and H:C ratios (Chen et al., 2011), but in this work we provide further information on the yields of various oxygenated functional groups, such as carbonyl and carboxylic CO, alcohol COH and organonitrate ONO2. In this work the organic aerosol functional group distribution predicted using MCM model is compared to chamber studies that use FTIR as the analytical technique in order to test its prediction capabilities of the functional group distribution of organic aerosol. Carbonyl and carboxylic CO, alcohol OH, alkane CH and organonitrate CONO2 relative fractions of the OA (Organic Aerosol) simulated were compared with the results of photooxidation and ozonolysis of α-pinene and trimethyl benzene in environmental controlled chamber experiments found in literature (Sax et al., 2005; Holes et al., 2007; Chhabra et al., 2011). The alkane CH, carbonyl CO and alcohol OH fraction are found to be well predicted by MCM for α- pinene, suggesting that the chemical pathways responsible for the addition of these functional groups to the parent VOC may be occurring predominantly in the gas phase. The nitrate and carboxylic acid fractions are less well predicted for the organic aerosol derived by α- pinene photooxidation. This may suggest that the condensed phase chemistry plays an important role in the formation or depletion of these functional groups from the organic mixture. This study contributes to understand how well the MCM model, widely used by the community, can predict aerosol phase functional group abundances in different scenarios and which kind of chemical reaction possibly occurring in the aerosol phase should be included to diminish the gap.