Abstract
Abstract. Using measurements from the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) experiment, we show that methyl peroxy nitrate (CH3O2NO2) is present in concentrations of ~5–15 pptv in the springtime arctic upper troposphere. We investigate the regional and global effects of CH3O2NO2 by including its chemistry in the GEOS-Chem 3-D global chemical transport model. We find that at temperatures below 240 K inclusion of CH3O2NO2 chemistry results in decreases of up to ~20 % in NOx, ~20 % in N2O5, ~5 % in HNO3, ~2 % in ozone, and increases in methyl hydrogen peroxide of up to ~14 %. Larger changes are observed in biomass burning plumes lofted to high altitude. Additionally, by sequestering NOx at low temperatures, CH3O2NO2 decreases the cycling of HO2 to OH, resulting in a larger upper tropospheric HO2 to OH ratio. These results may impact some estimates of lightning NOx sources as well as help explain differences between models and measurements of upper tropospheric composition.
Highlights
Non-acyl peroxynitrates (e.g. HO2NO2, CH3O2NO2) are weakly bound molecules that play a role in the chemistry of the troposphere where it is cold (Slusher et al, 2002; Murphy et al, 2004; Kim et al, 2007) or where peroxy radicals and NOx (NOx = NO + NO2) have especially high concentrations (Spencer et al, 2009)
A Laser Induced Fluorescence b Chemical ionization mass spectrometry c Proton transfer reaction mass spectrometry d Gas chromatography – mass spectrometry e Tunable diode laser absorption spectroscopy the NASA Intercontinental Chemical Transport ExperimentNorth America (INTEX-NA) demonstrated that HO2NO2 is present in the mid-latitude upper troposphere at mixing ratios of approximately 76 pptv between 8 and 9 km, accounting for about 5 % of NOy and 10 % of the local HOx sink (Kim et al, 2007)
Measurements from Aircraft and Satellites (ARCTAS) indicate that the thermally unstable CH3O2NO2 dissociates in the inlet of NO2 instruments resulting in upper tropospheric measurements of NO2 that are better described as thermally labile nitrogen (XNO2)
Summary
During the NCAR Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment (Atlas et al, 2003), measurements in the Arctic upper troposphere, where temperatures were on average ∼230 K, showed that non-acyl peroxy nitrates, primarily HO2NO2, were on average, 30 % of NOy (NOy = NO + NO2 + HO2NO2 + CH3O2NO2 + HNO3 + HONO + acyl peroxy nitrates + organic nitrates + NO3 + 2 N2O5) (Murphy et al, 2004) These observations imply that HO2NO2 represents a significant sink of HOx and acts as a large reservoir of NOx in the Arctic during winter and spring.
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