Atmospheric Gas-Phase Formation of Methanesulfonic Acid

Area of Science:

• Atmospheric Chemistry
• Climate Science

Background:

• The oxidation of dimethyl sulfide (DMS) is a key process influencing atmospheric composition and climate.
• The precise mechanism for methanesulfonic acid (MSA) formation from DMS oxidation remains incompletely understood.
• Known DMS oxidation pathways yield various intermediates including methanesulfinic acid (MSIA), methane sulfenic acid (MSEA), methylthio radical (CH3S), and hydroperoxymethyl thioformate (HPMTF).

Purpose of the Study:

• To elucidate the detailed chemical mechanism of methanesulfonic acid (MSA) formation from dimethyl sulfide (DMS) oxidation.
• To investigate the role of temperature in the branching ratios of DMS oxidation products.
• To assess the impact of a newly proposed temperature-sensitive MSA formation pathway on global atmospheric MSA burdens.

Main Methods:

• Theoretical calculations were employed to explore reaction pathways and intermediate product formation.
• Kinetic analysis was used to determine branching ratios and temperature dependencies.
• Global atmospheric modeling was utilized to simulate the effects of the proposed mechanism on MSA formation and burden.

Main Results:

• The methylthio radical (CH3SO2) can react with O2 to form CH3S(O)2OO, a precursor to MSA.
• The yield of MSA is highly sensitive to temperature, increasing significantly as temperatures decrease.
• SO2 is the dominant oxidation product in warmer regions, while MSA formation is favored in colder regions.

Conclusions:

• A novel, temperature-dependent mechanism for MSA formation from DMS oxidation has been identified.
• This mechanism explains the increased MSA yield at lower temperatures and has significant implications for atmospheric chemistry.
• The proposed mechanism leads to a substantial increase in simulated global atmospheric MSA formation and burden, highlighting its importance in climate regulation.