Measurements of the sum of HO2NO2 and CH3O2NO2 in the remote troposphere

[摘要] The chemistry of peroxynitric acid (HO₂NO₂) and methylperoxynitrate (CH₃O₂NO₂)is predicted to be particularlyimportant in the upper troposphere where temperatures are frequently lowenough that these compounds do not rapidly decompose. At temperatures below240K, we calculate that about 20% of NO_y in the mid- andhigh-latitude upper troposphere is HO₂NO₂. Under these conditions,the reaction of OH with HO₂NO₂ is estimated to account for as muchas one third of the permanent loss of hydrogen radicals. During theTropospheric Ozone Production about the Spring Equinox (TOPSE) campaign, weused thermal dissociation laser-induced fluorescence (TD-LIF) to measure thesum of peroxynitrates (PNs HO₂NO₂+CH₃O₂NO₂+PAN+PPN+...) aboard the NCAR C-130research aircraft. We infer the sum of HO₂NO₂ andCH₃O₂NO₂ as the difference between PN measurementsand gas chromatographic measurements of the two major peroxy acyl nitrates,peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparisonwith NO_y and other nitrogen oxide measurements confirms the importanceof HO₂NO₂ and CH₃O₂NO₂ to the reactive nitrogenbudget and shows that current thinking about the chemistry of these speciesis approximately correct. During the spring high latitude conditions sampledduring the TOPSE experiment, the model predictions of the contribution of(HO₂NO₂+CH₃O₂NO₂) to NO_y are highlytemperature dependent: on average 30% of NO_y at 230K, 15% ofNO_y at 240K, and 5% of NO_y above 250K. The temperaturedependence of the inferred concentrations corroborates the contribution ofovertone photolysis to the photochemistry of peroxynitric acid. A model thatincludes IR photolysis (J=1x10^-5s^-1) agreed with the observed sum ofHO₂NO₂+CH₃O₂NO₂ to better than 35% below 240K where the concentration of these species is largest.

[学科分类] 大气科学