[1] Observations of total alkyl nitrates (SANs) were obtained using thermal dissociationlaser-induced fluorescence at La Porte, Texas, from 15 August to 15 September 2000, along with an extensive suite of other nitrogen oxides, hydrocarbons, and O 3 . The SAN mixing ratios ranged as high as 5.2 ppbv. The median midday mixing ratio was 1.2 ppbv, and the median nighttime mixing ratio was 0.26 ppbv. These are higher mixing ratios than the sum of individual nitrates in virtually every prior study. The diurnal variation of SANs was similar to that of HNO 3 and of total peroxy nitrates, with a peak near 1300 local time (LT) indicating a photochemical source. Mixing ratios decreased rapidly in the afternoon, suggesting that SAN deposition is nearly as fast as HNO 3 deposition. The observed correlation between O 3 and SANs has a slope that increases from 29 (R 2 = 0.73) DO x /DSANs at 0900-1200 LT to 41 (R 2 = 0.74) DO x /DSANs at 1400-1800 LT. We present calculations constrained by the observed hydrocarbons showing that both the mixing ratio of SANs and the correlation of SANs with O 3 are to be expected on the basis of the branching ratios for alkyl nitrate formation in the RO 2 + NO reaction.

Abstract. The chemistry of peroxynitric acid (HO 2 NO 2 ) and methyl peroxynitrate (CH 3 O 2 NO 2 ) is predicted to be particularly important in the upper troposphere where temperatures are frequently low enough that these compounds do not rapidly decompose. At temperatures below 240 K, we calculate that about 20% of NO y in the mid-and high-latitude upper troposphere is HO 2 NO 2 . Under these conditions, the reaction of OH with HO 2 NO 2 is estimated to account for as much as one third of the permanent loss of hydrogen radicals. During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign, we used thermal dissociation laser-induced fluorescence (TD-LIF) to measure the sum of peroxynitrates ( PNs≡HO 2 NO 2 +CH 3 O 2 NO 2 +PAN+PPN+. . . ) aboard the NCAR C-130 research aircraft. We infer the sum of HO 2 NO 2 and CH 3 O 2 NO 2 as the difference between PN measurements and gas chromatographic measurements of the two major peroxy acyl nitrates, peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparison with NO y and other nitrogen oxide measurements confirms the importance of HO 2 NO 2 and CH 3 O 2 NO 2 to the reactive nitrogen budget and shows that current thinking about the chemistry of these species is approximately correct. During the spring high latitude conditions sampled during the TOPSE experiment, the model predictions of the contribution of (HO 2 NO 2 +CH 3 O 2 NO 2 ) to NO y are highly temperature dependent: on average 30% of NO y at 230 K, 15% of NO y at 240 K, and <5% of NO y above 250 K. The temperature dependence of the inferred concentrations corroborates the contribution of overtone photolysis to the photochemistry of peroxynitric acid. A model that includes IR photolysis (J=1×10 −5 s −1 ) agreed with the observed sum

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Abstract. The chemistry of peroxynitric acid (HO2NO2) and methyl peroxynitrate (CH3O2NO2) is predicted to be particularly important in the upper troposphere where temperatures are frequently low enough that these compounds do not rapidly decompose. At temperatures below 240 K, we calculate that about 20% of NOy in the mid and polar latitude upper troposphere is HO2NO2. Under these conditions, the reaction of OH with HO2NO2 is estimated to account for as much as one third of the permanent loss of hydrogen radicals. During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign, we used thermal dissociation laser-induced fluorescence (TD-LIF) to measure the sum of peroxynitrates (SPNs equivanlent HO2NO2 + CH3O2NO2 + PAN + PPN + ...), aboard the NCAR C-130 research aircraft. We infer the sum of HO2NO2 and CH3O2NO2 as the difference between SPN measurements and gas chromatographic measurements of the two major peroxy acyl nitrates, peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparison with NOy and other nitrogen oxide measurements confirms the importance of HO2NO2 and CH3O2NO2 to the reactive nitrogen budget and shows that current thinking about the chemistry of these species is approximately correct. The temperature dependence of the inferred concentrations corroborates the contribution of overtone photolysis to the photochemistry of peroxynitric acid.

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