Abstract
Abstract. The heterogeneous reaction of N2O5 on mixed organic-inorganic aerosol particles was investigated using an entrained aerosol flow tube coupled to a custom-built chemical ionization mass spectrometer. Laboratory results on aqueous particles confirm a strong dependence of the reactive uptake coefficient (γ) on particle liquid water, for particle water concentrations below 15 M, and the molar ratio of particle water to nitrate. Measurements of γ (N2O5) on mixed chloride-nitrate particles indicate that the presence of trace chloride can negate the suppression of γ(N2O5) at high nitrate loadings with implications for polluted coastal regions. These results are used to construct a new parameterization for γ (N2O5), that when coupled to an aerosol thermodynamics model, can be used within regional and/or global chemical transport models.
Highlights
The results indicate a strong dependence of γ (N2O5) on relative humidity (RH) below 50%, as previously observed in the Thornton et al study (2003)
The functional dependence of γ (N2O5) on RH is slightly different for NH4HSO4 as compared to malonic acid, due to possible differences in the hygroscopicity and the non-ideality of water in the resulting solutions (Braban and served γ (N2O5) to increase strongly with RH above 50% RH, which would imply that N2O5 hydrolysis is always limited by H2O(l)
The impact of N2O5 heterogeneous reactions on global tropospheric NOx and O3 was first explored by Dentener and Crutzen, where they employed a globally uniform γ (N2O5) of 0.1, based upon laboratory studies conducted under conditions most relevant to the stratosphere (Dentener and Crutzen, 1993). These results indicated that accurate representation of the heterogeneous hydrolysis of N2O5 was critical for understanding both NOx loadings and O3 production rates in the troposphere
Summary
The heterogeneous reaction of dinitrogen pentoxide (N2O5) on aerosol particles plays a critical role in regulating tropospheric reactive nitrogen (NOx≡NO + NO2) availability (Dentener and Crutzen, 1993), contributes to particulate nitrate (NO−3 ) loadings (Riemer et al, 2003) and promotes halogen activation following reaction on chloride containing particles (Behnke et al, 1997; Finlayson-Pitts et al, 1989; Osthoff et al, 2008; Thornton and Abbatt, 2005). We build upon the existing set of laboratory investigations of γ (N2O5), by directly probing the competing effects of Published by Copernicus Publications on behalf of the European Geosciences Union. A. Thornton: The competing effects of particle liquid water, nitrate and chloride particle liquid water content (H2O(l)), nitrate (NO−3 ) and chloride (Cl−) using internally mixed particles representative of the lower troposphere. We report γ (N2O5) for a series of mixed inorganic and organic aerosol particles over a wide range in H2O(l). These new measurements help test current mechanistic theories of N2O5 reactivity in aqueous solutions and aid the development of a more chemically accurate parameterization for γ (N2O5) that, when coupled to an aerosol thermodynamics model, can be used in chemical transport models
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