Reactivity and loss mechanisms of NO3 and N2O5 in a polluted marine environment: Results from in situ measurements during New England Air Quality Study 2002

Abstract

Concentrations of NO3 and N2O5 were measured using an in situ instrument aboard the NOAA research vessel Ronald H. Brown in 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 N2O5 losses allowed for a determination of its heterogeneous uptake coefficient and gave γ(N2O5) = 0.03 ± 0.02. Reactions of NO3 with 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 NO3 and N2O5 was rapid, and the partitioning between NO3 and N2O5 losses was roughly equal. Because rapid N2O5 loss consumes NOx at twice the rate of the reaction of NO2 with O3, whereas rapid NO3 loss leads to NOx removal at the same rate, the equal partitioning of losses indicates a nocturnal NOx loss rate of approximately 1.5 times the rate of NO2 + O3. Activation of halogens from the uptake of NO3 and N2O5 on sea salt was calculated to have produced substantial amounts of active Cl on some mornings through the nocturnal formation and sunrise photolysis of ClNO2 if 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.