Chamber simulation of photooxidation of dimethyl sulfide and isoprene in the presence of NO<sub>x</sub>

Abstract

Abstract. To improve the model prediction for the formation of H2SO4 and methanesulfonic acid (MSA), aerosol-phase reactions of gaseous dimethyl sulfide (DMS) oxidation products [e.g., dimethyl sulfoxide (DMSO)] in aerosol have been included in the DMS kinetic model with the recently reported gas-phase reactions and their rate constants. To determine the rate constants of aerosol-phase reactions of both DMSO and its major gaseous products [e.g., dimethyl sulfone (DMSO2) and methanesulfinic acid (MSIA)], DMSO was photooxidized in the presence of NOx using a 2 m3 Teflon film chamber. The rate constants tested in the DMSO kinetic mechanisms were then incorporated into the DMS photooxidation mechanism. The model simulation using the newly constructed DMS oxidation mechanims was compared to chamber data obtained from the phototoxiation of DMS in the presence of NOx. Within 120-min simulation, the predicted concentrations of MSA increase by 200–400% and those of H2SO4, by 50–200% due to aerosol-phase chemistry. This was well substantiated with experimental data. To study the effect of coexisting volatile organic compounds, the photooxidation of DMS in the presence of isoprene and NOx has been simulated using the newly constructed DMS kinetic model integrated with the Master Chemical Mechanism (MCM) for isoprene oxidation, and compared to chamber data. With the high concentrations of DMS (250 ppb) and isoprene (560–2248 ppb), both the model simulation and experimental data showed an increase in the yields of MSA and H2SO4 as the isoprene concentration increased.

Product distribution, kinetics, and aerosol formation from the OH oxidation of dimethyl sulfide under different RO2 regimes

“…1 were SO 2 , particulate MSA, and particulate sulfate, with 48 % of the product sulfur found in the particle phase. The measured MSA : sulfate ratio (∼ 2.5 : 1) is in broad agreement with those reported in Chen et al (2012). Minor species observed included dimethyl sulfoxide (DMSO), C 2 H 6 SO 2 (likely dimethyl sulfone, DMSO 2 ), and methane sulfinic acid (MSIA), known products from the addition channel, as well as CH 2 SO 2 (likely a thioacid, which may be formed as an OH oxidation product of HPMTF, Jernigan et al, 2022a) and CH 3 SO 6 N (likely methanesulfonyl peroxynitrate, formed from CH 3 S(O) 2 OO + NO 2 ).…”

The Methylsulfonyloxyl Radical, CH3SO3

“…[3] Despite there being many laboratory simulations of DMS oxidation, the underlying mechanism remains largely unknown because of the complexity of many reaction channels involving short-lived radical species,a nd al arge discrepancy still exits between the experimental measurements and simulation results. [4] According to the frequently applied kinetic model, the oxidation of DMS in the gas phase occurs through as tepwise formation of radical species CH 3 SO x (x = 0-3). [5] Thef inal radical species,C H 3 SO 3 ,c an either dissociate into CH 3 and SO 3 followed by H 2 SO 4 formation, abstract hydrogen from atmospheric volatile organic compounds R-H to produce MSA, or react with NO 2 to give methylsulfonyl nitrate,C H 3 SO 3 NO 2 .…”

“…Despite there being many laboratory simulations of DMS oxidation, the underlying mechanism remains largely unknown because of the complexity of many reaction channels involving short‐lived radical species, and a large discrepancy still exits between the experimental measurements and simulation results 4. According to the frequently applied kinetic model, the oxidation of DMS in the gas phase occurs through a stepwise formation of radical species CH 3 SO x ( x =0–3) 5.…”

Supplementary material to "Modelling Atmospheric Mineral Aerosol Chemistry to Predict Heterogeneous Photooxidation of SO<sub>2</sub>"

“…The unit of the rate constants for the dust sorption reactions is m 3 m -2 s -1 . b The rate constant parameters of SO2 oxidation in gas phase are taken from previous studies as shown in note of each reactions and can be also found in Chen and Jang (2012). T (K) is the temperature.…”