Kinetic and mechanistic study of the reaction between methane sulfonamide (CH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;S(O)&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;NH&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) and OH

Matias Berasategui,John N Crowley,Achim Edtbauer,Damien Amedro,Jonathan Williams,Jos Lelieveld

doi:10.5194/acp-20-2695-2020

Kinetic and mechanistic study of the reaction between methane sulfonamide (CH&lt;sub&gt;3&lt;/sub&gt;S(O)&lt;sub&gt;2&lt;/sub&gt;NH&lt;sub&gt;2&lt;/sub&gt;) and OH

Matias Berasategui, John N Crowley + Show 4 more

Open Access

https://doi.org/10.5194/acp-20-2695-2020

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Abstract

Abstract. Methane sulfonamide (MSAM), CH3S(O)2NH2, was recently detected for the first time in ambient air over the Red Sea and the Gulf of Aden where peak mixing ratios of ≈60 pptv were recorded. Prior to this study the rate constant for its reaction with the OH radical and the products thereby formed were unknown, precluding assessment of its role in the atmosphere. We have studied the OH-initiated photo-oxidation of MSAM in air (298 K, 700 Torr total pressure) in a photochemical reactor using in situ detection of MSAM and its products by Fourier transform infrared (FTIR) absorption spectroscopy. The relative rate technique, using three different reference compounds, was used to derive a rate coefficient of (1.4±0.3)×10-13cm3molec.-1s-1. The main end products of the photo-oxidation observed by FTIR were CO2, CO, SO2, and HNO3 with molar yields of (0.73±0.11), (0.28±0.04), (0.96±0.15), and (0.62±0.09), respectively. N2O and HC(O)OH were also observed in smaller yields of (0.09±0.02) and (0.03±0.01). Both the low rate coefficient and the products formed are consistent with hydrogen abstraction from the −CH3 group as the dominant initial step. Based on our results MSAM has an atmospheric lifetime with respect to loss by reaction with OH of about 80 d.

Highlights

IntroductionNatural emissions of organosulfur compounds from phytoplankton comprise up to 60 % of the total sulfur flux into the marine boundary layer (Andreae, 1990; Bates et al, 1992; Spiro et al, 1992), and in remote oceanic areas they are the main source of climatically active sulfate aerosols, which can influence the radiation balance at the earth’s surface (Charlson et al, 1987; Andreae and Crutzen, 1997).The main organosulfur trace gases in the marine boundary layer are dimethyl sulfide (CH3SCH3, DMS) and its oxidation products dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2), methyl sulfonic acid (MSA), and methyl sulfinic acid (MSI) for which atmospheric lifetimes with respect to their degradation by the OH radical vary between hours (DMS) and several weeks (DMSO2).Recently, the first detection of methane sulfonamide (CH3S(O)2NH2, MSAM) in ambient air was made during the Air Quality and Climate Change in the Arabian Basin (AQABA-2017) campaign
The first detection of methane sulfonamide (CH3S(O)2NH2, MSAM) in ambient air was made during the Air Quality and Climate Change in the Arabian Basin (AQABA-2017) campaign
As MSAM had not been considered to be an atmospheric trace gas prior to the observations of Edtbauer et al (2019), there have been no laboratory studies to investigate either its spectroscopy or the kinetics of its reactions with atmospheric radicals, such as OH, so that its atmospheric lifetime and the products formed during its degradation in air were unknown

Summary

Introduction

Natural emissions of organosulfur compounds from phytoplankton comprise up to 60 % of the total sulfur flux into the marine boundary layer (Andreae, 1990; Bates et al, 1992; Spiro et al, 1992), and in remote oceanic areas they are the main source of climatically active sulfate aerosols, which can influence the radiation balance at the earth’s surface (Charlson et al, 1987; Andreae and Crutzen, 1997).The main organosulfur trace gases in the marine boundary layer are dimethyl sulfide (CH3SCH3, DMS) and its oxidation products dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2), methyl sulfonic acid (MSA), and methyl sulfinic acid (MSI) for which atmospheric lifetimes with respect to their degradation by the OH radical vary between hours (DMS) and several weeks (DMSO2).Recently, the first detection of methane sulfonamide (CH3S(O)2NH2, MSAM) in ambient air was made during the Air Quality and Climate Change in the Arabian Basin (AQABA-2017) campaign. The main organosulfur trace gases in the marine boundary layer are dimethyl sulfide (CH3SCH3, DMS) and its oxidation products dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2), methyl sulfonic acid (MSA), and methyl sulfinic acid (MSI) for which atmospheric lifetimes with respect to their degradation by the OH radical vary between hours (DMS) and several weeks (DMSO2). As MSAM had not been considered to be an atmospheric trace gas prior to the observations of Edtbauer et al (2019), there have been no laboratory studies to investigate either its spectroscopy or the kinetics of its reactions with atmospheric radicals, such as OH, so that its atmospheric lifetime and the products formed during its degradation in air were unknown. Unlike basic alkyl amines such as, for example, CH3NH2, MSAM contains an acidic −NH2 group (Remko, 2003)

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