High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures

Abstract

Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H 2 SO 4 ). Despite their importance, accurate prediction of MSA and H 2 SO 4 from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to −10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H 2 SO 4 production is modestly affected. This leads to a gas-phase H 2 SO 4 -to-MSA ratio (H 2 SO 4 /MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH 3 S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2–10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NO x effect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H 2 SO 4 /MSA measurements.

Reaction of Atmospherically Relevant Sulfur-Centered Radicals with RO2 and HO2

“…In recent DMS + OH oxidation experiments, compounds with the chemical formula CH 4 SO n (n = 2−4) have been detected by mass spectrometry. 39,40 Based on the known DMS oxidation mechanism, the compound with the formula CH 4 SO 4 has only one viable structure, CH 3 S(O) 2 OOH, in line with our calculations that this hydroperoxide is thermally stable. The compound with the formula CH 4 SO 3 has two potential structures, CH 3 S(O) 2 OH (methanesulfonic acid, MSA) and CH 3 S(O)OOH.…”

“…The formation of CH 3 S(O) 2 OO (n = 2) has been experimentally confirmed by the detection of its corresponding peroxy nitrate, CH 3 S(O) 2 OONO 2 . 39,40 Following the accretion product formation mechanism, CH 3 S-(O) n OOCH 3 and CH 3 S(O) n OOH (n = 0−2) can potentially form as the accretion products from CH 3 S(O) n OO (n = 0−2) reacting with CH 3 OO and HOO (Section S5), with the same stability issues as discussed previously. The observed peroxides CH 3 S(O) 2 OOR and CH 3 S(O) 2 OOH are likely formed from the accretion mechanism instead of the CH 3 SO 2 + RO 2 or HO 2 reaction.…”

Measurement of the Intramolecular Hydrogen-Shift Rate Coefficient for the CH3SCH2OO Radical between 314 and 433 K

“…The atmospheric formation and fate of HPMTF and its potential impact on sulfate aerosol formation is a topic of active research in the atmospheric chemistry community. In addition to the present HPMTF experimental laboratory studies and that in other laboratories, ,,,, there have been a number of field ,, and atmospheric modeling studies of HPMTF. ,− Field observations have demonstrated that HPMTF is present in the global marine boundary layer ,, and the Amazonian basin with a diurnal profile and that it is efficiently removed when encountering a cloud, , which implies efficient uptake by cloud droplets. The uptake coefficient and fate of HPMTF and its degradation mechanism in the aqueous phase, however, remain a research topic of interest …”

“…These results compare favorably with the theoretical calculations presented in the seminal HOOCH 2 SCHO (HPMTF) study of Veres et al 11 and the theoretical value from Jernigan et al 15 The atmospheric formation and fate of HPMTF and its potential impact on sulfate aerosol formation is a topic of active research in the atmospheric chemistry community. In addition to the present HPMTF experimental laboratory studies and that in other laboratories, 12,13,15,49,50 there have been a number of field 11, 51,52 and atmospheric modeling studies of HPMTF. 11,52−56 Field observations have demonstrated that HPMTF is present in the global marine boundary layer 11,51,52 and the Amazonian basin 57 with a diurnal profile and that it is efficiently removed when encountering a cloud, 11,52 which implies efficient uptake by cloud droplets.…”

“…Therefore, we have made some reasonable assumptions for a back-of-the-envelope calculation. First, we assume representative concentrations of NO, HO 2 , or RO 2 in the remote atmosphere of ∼10 8 to 10 9 molecule cm –3 and [OH] = ∼10 6 molecule cm –1 ,, and assuming rate coefficients for the reactions of MSP with NO/HO 2 /RO 2 of ∼1 × 10 –11 molecule cm 3 s –1 and MSP with OH of ∼1 × 10 –10 molecule cm 3 s –1 . The total first-order removal rate coefficient of MSP from bimolecular reactions would be in the range ∼0.003–0.03 s –1 .…”