Measurements of CH3O2NO2 in the upper troposphere

Methyl peroxy nitrate (CH3 O2 NO2 ) is a nonacyl peroxy nitrate that is important for photochemistry at low temperatures characteristic of the upper troposphere. We report the first measurements of CH3 O2 NO2 , 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 CH3 O2 NO2 measurements. CH3 O2 NO2 is predicted to be a ubiquitous interference to upper-tropospheric NO2 measurements. We describe an experimental strategy for obtaining NO2 observations free of the CH3 O2 NO2 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 CH3 O2 NO2 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 (HO2 NO2 ) to the CH3 O2 NO2 measurements, as HO2 NO2 partially decomposes (∼ 11 %) along with CH3 O2 NO2 in the heated CH3 O2 NO2 channel used to detect CH3 O2 NO2 .