DC3 brought together simultaneous measurements of storm kinematics, structure, electrical activity, and chemistry to improve our knowledge of how thunderstorms affect the chemical composition of the troposphere.

NOx (NOx ≡ NO + NO2) regulates O3 and HOx (HOx ≡ OH + HO2) concentrations in the upper troposphere. In the laboratory, it is difficult to measure rates and branching ratios of the chemical reactions affecting NOx at the low temperatures and pressures characteristic of the upper troposphere, making direct measurements in the atmosphere especially useful. We report quasi-Lagrangian observations of the chemical evolution of an air parcel following a lightning event that results in high NOx concentrations. These quasi-Lagrangian measurements obtained during the Deep Convective Clouds and Chemistry experiment are used to characterize the daytime rates for conversion of NOx to different peroxy nitrates, the sum of alkyl and multifunctional nitrates, and HNO3. We infer the following production rate constants [in (cm(3)/molecule)/s] at 225 K and 230 hPa: 7.2(±5.7) × 10(-12) (CH3O2NO2), 5.1(±3.1) × 10(-13) (HO2NO2), 1.3(±0.8) × 10(-11) (PAN), 7.3(±3.4) × 10(-12) (PPN), and 6.2(±2.9) × 10(-12) (HNO3). The HNO3 and HO2NO2 rates are ∼ 30-50% lower than currently recommended whereas the other rates are consistent with current recommendations to within ±30%. The analysis indicates that HNO3 production from the HO2 and NO reaction (if any) must be accompanied by a slower rate for the reaction of OH with NO2, keeping the total combined rate for the two processes at the rate reported for HNO3 production above.

Abstract. Methyl peroxy nitrate (CH 3 O 2 NO 2 ) is a nonacyl peroxy nitrate that is important for photochemistry at low temperatures characteristic of the upper troposphere. We report the first measurements of CH 3 O 2 NO 2 , which we achieved through a new aircraft inlet configuration, combined with thermal-dissociation laser-induced fluorescence (TD-LIF) detection of NO 2 , and describe the accuracy, specificity, and interferences to CH 3 O 2 NO 2 measurements. CH 3 O 2 NO 2 is predicted to be a ubiquitous interference to upper-tropospheric NO 2 measurements. We describe an experimental strategy for obtaining NO 2 observations free of the CH 3 O 2 NO 2 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 CH 3 O 2 NO 2 measurements we report have a detection limit (S/N = 2) of 15 pptv at 1 min averaging on a background of 200 pptv NO 2 and an accuracy of ±40 %. Observations are used to constrain the interference of pernitric acid (HO 2 NO 2 ) to the CH 3 O 2 NO 2 measurements, as HO 2 NO 2 partially decomposes (∼ 11 %) along with CH 3 O 2 NO 2 in the heated CH 3 O 2 NO 2 channel used to detect CH 3 O 2 NO 2 .

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Abstract. The non-acyl peroxy nitrates, HO2NO2 and CH3O2NO2, are predicted to be important for photochemistry at low temperatures characteristic of the upper troposphere. We report the first measurements of methyl peroxy nitrate (CH3O2NO2). During 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, different inlet configurations for the UC Berkeley Thermal Dissociation-Laser Induced Instrument were tested to optimize measurements of CH3O2NO2 from the NASA DC-8. In addition, the inlet modifications were optimized for measurements of NO2 without CH3O2NO2 interferences. The CH3O2NO2 measurements we report have a detection limit (S/N = 2) of 15 pptv (parts per trillion by volume) at 1 min averaging on a background of 200 pptv NO2 and an accuracy of ±40%. Both observations and theoretical calculations were used to constrain the interference of pernitric acid (HO2NO2), which partially decomposes (~ 11%) along with CH3O2NO2 in our heated CH3O2NO2 channel. Evaluation of the accuracy of the CH3O2NO2 measurements is presented.