Abstract
The uptake of dinitrogen pentoxide (N2O5) on aerosols affects the nocturnal removal of NOx and particulate nitrate formation in the atmosphere. This study investigates N2O5 uptake processes using field observations from an urban site in Beijing during April–May 2017, a period characterized by dry weather conditions. For the first time, a very large N2O5 uptake rate (k(N2O5) up to ~0.01 s−1) was observed during a sand storm event, and the uptake coefficient (γ(N2O5)) was estimated to be 0.044. The γ(N2O5) in urban air masses was also determined and exhibited moderate correlation (r = 0.68) with aerosol volume to surface ratio (Va/Sa), but little relation to aerosol water, nitrate, and chloride, a finding that contrasts with previous results. Several commonly used parameterizations of γ(N2O5) underestimated the field-derived γ(N2O5). A new parameterization is suggested for dry conditions, which considers the effect of Va/Sa, temperature, and relative humidity.
Highlights
Dinitrogen pentoxide (N2 O5 ) is an important nighttime reservoir of NOx which is a key precursor to photochemical production of ozone [1]
The present study examines the heterogeneous uptake of N2 O5 based on field measurements in urban Beijing during April and May 2017, when relative humidity (RH) was low (27 ± 18%, average ± standard deviation) and dust storms took place
Measurement results for N2 O5, ClNO2, and related chemical and meteorological parameters
Summary
Dinitrogen pentoxide (N2 O5 ) is an important nighttime reservoir of NOx which is a key precursor to photochemical production of ozone [1]. Laboratory studies have found that N2 O5 uptake is enhanced by chloride and aerosol water content ([H2 O]). Laboratory studies have suggested large γ(N2 O5 ) on mineral dust, there have been no reports on direct observations of N2 O5 uptake on ambient mineral dust. Several parameterizations of γ(N2 O5 ) have been proposed to predict γ(N2 O5 ) based on laboratory results on the relation of γ(N2 O5 ) to temperature, relative humidity (RH), aerosol size, and aerosol inorganic and organic content (e.g., [14,16,25,26]). The present study examines the heterogeneous uptake of N2 O5 based on field measurements in urban Beijing during April and May 2017, when RH was low (27 ± 18%, average ± standard deviation) and dust storms took place.
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