Abstract
Abstract. This paper describes a modelling study of several HOx and NOx species (OH, HO2, organic peroxy radicals, NO3 and N2O5) in the marine boundary layer. A model based upon the Master Chemical Mechanism (MCM) was constrained to observations of chemical and physical parameters made onboard the NOAA ship R/V Brown as part of the New England Air Quality Study (NEAQS) in the summer of 2004. The model was used to calculate [OH] and to determine the composition of the peroxy radical pool. Modelled [NO3] and [N2O5] were compared to in-situ measurements by Cavity Ring-Down Spectroscopy. The comparison showed that the model generally overestimated the measurements by 30–50%, on average. The model results were analyzed with respect to several chemical and physical parameters, including uptake of NO3 and N2O5 on fog droplets and on aerosol, dry deposition of NO3 and N2O5, gas-phase hydrolysis of N2O5 and reactions of NO3 with NMHCs and peroxy radicals. The results suggest that fog, when present, is an important sink for N2O5 via rapid heterogeneous uptake. The comparison between the model and the measurements were consistent with values of the heterogeneous uptake coefficient of N2O5 (γN2O5)>1×10−2, independent of aerosol composition in this marine environment. The analysis of the different loss processes of the nitrate radical showed the important role of the organic peroxy radicals, which accounted for a significant fraction (median: 15%) of NO3 gas-phase removal, particularly in the presence of high concentrations of dimethyl sulphide (DMS).
Highlights
Production and loss of radical species control the oxidation of tropospheric trace gases, such as CO, CH4 and Non Methane Hydrocarbons (NMHCs)
This paper presents model calculations of the concentrations of OH and NO3 from a ship-based field campaign (NEAQS 2004); the main focus of the work was on nighttime radical chemistry, principally NO3, since there were in-situ measurements of these species that could be compared with the model results
During the New England Air Quality Study (NEAQS) 2004 campaign the NOAA research vessel R/V Brown cruised off the coast of New England measuring, among other chemical and physical parameters, radical species and their precursors
Summary
Production and loss of radical species control the oxidation of tropospheric trace gases, such as CO, CH4 and Non Methane Hydrocarbons (NMHCs). The sources of these radicals vary greatly within a diurnal cycle. This paper presents model calculations of the concentrations of OH and NO3 from a ship-based field campaign (NEAQS 2004); the main focus of the work was on nighttime radical chemistry, principally NO3 (and, by extension, N2O5), since there were in-situ measurements of these species that could be compared with the model results.
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