Influence of nitrate radical on the oxidation of dimethyl sulfide in a polluted marine environment

Simultaneous in situ measurements of dimethyl sulfide (DMS) and nitrate radical (NO3) from the NOAA research vessel Ronald H. Brown off the New England Coast during the summer of 2002 show a clear anticorrelation between these compounds. The anticorrelation indicates a strong interaction between anthropogenic NOx emissions and natural sulfur emissions from the ocean surface. The anticorrelation was invariant with the distance from the continent over the range sampled during this study. Diurnal averages showed maxima in DMS concentrations during dawn and dusk and a lower minimum of approximate to 30 pptv at night compared to the daytime minimum of approximate to 40 pptv, indicating a stronger oxidation by NO3 at night than by OH at daytime under polluted conditions. This conclusion is also supported by agreement between a box model calculation and the measurements. Including DMS oxidation by halogens (Cl and BrO) into the model improved the agreement significantly. Calculation of the relative DMS loss due to either NO3 or OH oxidation indicated that between 65 and 90% of the DMS oxidation was due to NO3, depending on NO3 mixing ratios. The area over which DMS oxidation by NO3 is at least as strong as by OH can extend as far as 3000 km from coastal anthropogenic NOx sources. These increased DMS oxidation rates by NO3 may have an impact on global non-sea-salt sulfate aerosol production, depending on the DMS chemical oxidation mechanism.