Flux divergence of nitric acid in the marine atmospheric surface layer

International audienceIt is hypothesized that removal of HNO 3 from the atmosphere close to the sea surface is due to two processes: dry deposition to the sea surface and chemical reaction with sea spray. The latter process invalidates the application of the constant flux layer assumption to calculate dry deposition based on concentrations of HNO 3 at, e.g., a reference height of 10 m. A field experiment was carried out to investigate this hypothesis, and the measured concentration profiles were found to differ dramatically from the log linear profiles, which would have been produced by turbulent transport only. Surface fluxes of HNO 3 were calculated from the measured profiles taking chemical reactions into account and were compared to surface fluxes calculated by the traditional resistance method. It was found that the surface fluxes could be a factor of two less when chemical reactions are taken into account, depending on the characteristics of the near-surface aerosols. HNO 3 loss rates due to heterogeneous chemistry are calculated by two independent methods and are compared