The influence of the nitrate radical on the dimethylsulfide oxidation derived from field measurements during NEAQS (New England Air Quality Study)

We present simultaneous measurements of nitrate radical (NO₃) and dimethylsulfide (DMS) from NEAQS (New England Air Quality Study). DMS is emitted from the ocean surface as a result of phytoplankton activity, whereas NO₃ is produced by reaction of ozone (O₃) and nitrogen dioxide (NO₂) in polluted air. Photolysis by visible light and rapid reaction with NO during daytime prevent NO₃ from building to significant concentration, except at night. The rapid reaction between NO₃ and DMS constitutes an important sink for the latter in the polluted marine boundary layer. We will show nocturnal profiles of both compounds as well as the anticorrelations between them. These data indicate that nighttime DMS oxidation by NO₃ under polluted conditions with high NO₃ concentrations in the north-east coastal region of the US and daytime oxidation by OH are comparable. We will discuss the influence of transport and mixing of fresh emissions into marine air on the observed anticorrelations based on trajectory calculations and tracer measurements to distinguish between transport effects and reactions.