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Concentrations of NO3and N2O5were measured using an in situ instrument aboard the NOAA research vessel Ronald H. Brownin the marine boundary layer along the United States east coast as part of the New England Air Quality Study (NEAQS) in the summer of 2002. We analyze the results in terms of the loss partitioning and sink budgets for both of these compounds. Analysis of the data on nights with large N2O5losses allowed for a determination of its heterogeneous uptake coefficient and gave γ(N2O5) = 0.03 ± 0.02. Reactions of NO3with terrestrially emitted biogenic volatile organic compounds (isoprene and monoterpenes), advected into the marine boundary layer, and with DMS emitted from the ocean surface were also important. In general, loss of NO3and N2O5was rapid, and the partitioning between NO3and N2O5losses was roughly equal. Because rapid N2O5loss consumes NOxat twice the rate of the reaction of NO2with O3, whereas rapid NO3loss leads to NOxremoval at the same rate, the equal partitioning of losses indicates a nocturnal NOxloss rate of approximately 1.5 times the rate of NO2+ O3. Activation of halogens from the uptake of NO3and N2O5on sea salt was calculated to have produced substantial amounts of active Cl on some mornings through the nocturnal formation and sunrise photolysis of ClNO2if the process proceeded at the rate determined by laboratory studies. However, there was no direct observational evidence to test the magnitude of the predicted source.

The nitrate radical, NO3, and dinitrogen pentoxide, N2O5, are key reactive nocturnal nitrogen oxides in the troposphere. The daytime impact of NO3and N2O5, however, is restricted by photochemical recycling of NO3to NO2and O3. In this paper, we report daytime measurements of N2O5on board the NOAA research vessel Ronald H. Brownin the Gulf of Maine during the New England Air Quality Study–Intercontinental Transport and Chemical Transformation (NEAQS‐ITCT) campaign in the summer of 2004. Daytime N2O5mixing ratios of up to 4 pptv were observed, consistent with predictions from a steady state analysis. Predicted and observed NO3mixing ratios were below the instrumental detection limit of ∼1 pptv; the average calculated concentration was 0.09 pptv. Important impacts of daytime NO3and N2O5in the marine boundary layer included increased rates of VOC oxidation (in particular dimethyl sulfide) and enhanced NOxto HNO3conversion, both of which scaled with the available NOx. Smaller effects of daytime NO3and N2O5included chemical destruction of O3and a shift of the NO2:NO ratio. Because the rates of heterogeneous conversion of N2O5and NO3to HNO3scale with the surface area available for uptake, the importance of daytime fog is discussed.