DMS and MSA measurements in the Antarctic Boundary Layer: impact of BrO on MSA production

[摘要] In situ measurements of dimethyl sulphide (DMS) and methane sulphonic acid(MSA) were made at Halley Station, Antarctica (75°35' S, 26°19' W)during February 2004–February 2005 as part of the CHABLIS (Chemistry of theAntarctic Boundary Layer and the Interface with Snow) project. DMS waspresent in the atmosphere at Halley all year (average 38.1±43 pptV)with a maximum monthly average value of 113.6±52 pptV in February2004 coinciding temporally with a minimum in sea extent. Whilst seasonalvariability and interannual variability can be attributed to a number offactors, short term variability appeared strongly dependent on air massorigin and trajectory pressure height. The MSA and derived non-sea saltsulphate (nss-SO₄²⁻) measurements showed no correlation with thoseof DMS (regression R²=0.039, and R²=0.001 respectively)in-line with the complexity of DMS fluxes, alternative oxidation routes,transport of air masses and variable spatial coverage of both sea-ice andphytoplankton. MSA was generally low throughout the year, with an annualaverage of 42 ng m⁻³ (9.8±13.2 pptV), however MSA:nss-SO₄²⁻ ratios were high implying a dominance of the additionoxidation route for DMS. Including BrO measurements into MSA productioncalculations demonstrated the significance of BrO on DMS oxidation withinthis region of the atmosphere in austral summer. Assuming an 80% yieldof DMSO from the reaction of DMS+BrO, an atmospheric concentration of BrOequal to 3 pptV increased the calculated MSA production from DMS by a factorof 9 above that obtained when considering only reaction with the hydroxylradical. These findings have significant atmospheric implications, but mayalso impact on the interpretation of ice cores which previously relied onthe understanding of MSA and nss-SO₄²⁻ chemistry to provideinformation on environmental conditions such as sea ice extent and theorigins of sulphur within the ice.

[学科分类] 大气科学