Nighttime nitrate radical chemistry at Appledore Island, Maine during the 2004 International Consortium for Atmospheric Research on Transport and Transformation

Abstract

Trace gases including nitrogen dioxide (NO 2), nitrate radical (NO 3), ozone (O 3), and a suite of volatile organic compounds (VOCs) were measured within the New England coastal marine boundary layer on Appledore Island (AI), Maine, USA as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign. These measurements, together with local meteorological records and published kinetic data were used to investigate nighttime NO 3 chemistry at AI during the period of 8-28 July 2004. Among the VOCs, isoprene, monoterpenes and dimethylsulfide (DMS) were the dominant NO 3 reactants; on average, DMS accounted for 51 ± 34% of the total reactivity. For three case studies, NO 3 mixing ratios were calculated from measured parameters with resultant uncertainties of ≤30%. Discrepancies with measured NO 3 appeared to result primarily from input parameter variability and exclusion of heterogeneous dinitrogen pentoxide (N 2 O 5) chemistry. We indirectly determined that nighttime NO 3 and NO x (=NO + NO 2) removal via N 2 O 5 chemistry (gas-phase + heterogeneous) was on average 51-54% and 63-66% of the total respectively. Our analysis suggested that the minimum average NO 3 and NO x removal via heterogeneous N 2 O 5 chemistry was ∼10% of the total. Reducing gas-phase N 2 O 5 reactivity in accord with Brown et al. (2006a) increased the importance of heterogeneous N 2 O 5 chemistry substantially. It is plausible that the latter pathway was often comparable to gas-phase removal of NO 3 and NO x. Overall, 24 h-averaged NO x removal was ∼11 ppbv, with nighttime chemical pathways contributing ∼50%. Copyright 2007 by the American Geophysical Union.