Articles | Volume 8, issue 2
Research article
27 Feb 2015
Research article |  | 27 Feb 2015

Measurements of CH3O2NO2 in the upper troposphere

B. A. Nault, C. Garland, S. E. Pusede, P. J. Wooldridge, K. Ullmann, S. R. Hall, and R. C. Cohen

Abstract. Methyl peroxy nitrate (CH3O2NO2) is a non-acyl peroxy nitrate that is important for photochemistry at low temperatures characteristic of the upper troposphere. We report the first measurements of CH3O2NO2, which we achieved through a new aircraft inlet configuration, combined with thermal-dissociation laser-induced fluorescence (TD-LIF) detection of NO2, and describe the accuracy, specificity, and interferences to CH3O2NO2 measurements. CH3O2NO2 is predicted to be a ubiquitous interference to upper-tropospheric NO2 measurements. We describe an experimental strategy for obtaining NO2 observations free of the CH3O2NO2 interference. Using these new methods, we made observations during two recent aircraft campaigns: the Deep Convective Clouds and Chemistry (DC-3) and the Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS) experiments. The CH3O2NO2 measurements we report have a detection limit (S/N = 2) of 15 pptv at 1 min averaging on a background of 200 pptv NO2 and an accuracy of ±40%. Observations are used to constrain the interference of pernitric acid (HO2NO2) to the CH3O2NO2 measurements, as HO2NO2 partially decomposes (~11%) along with CH3O2NO2 in the heated CH3O2NO2 channel used to detect CH3O2NO2.

Short summary
We report the first atmospheric measurement of methyl peroxy nitrate (CH3O2NO2) and describe an experimental strategy to obtain NO2 observations free of methyl peroxy nitrate (CH3O2NO2). The accuracy of the CH3O2NO2 measurements are (+/- 40%) with a LOD of 15 pptv/min. We observe that CH3O2NO2 is ubiquitous in the upper troposphere with median mixing ratios of 100 to 200 pptv, and its composition to the total NOy budget is comparable to HNO3.