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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 NOy 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 (<IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img4.gif" ALT="$Sigma$">PNs<IMG WIDTH="15" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img5.gif" ALT="$equiv$"> HO2NO2+CH3O2NO2+PAN+PPN+...) aboard the NCAR C-130research aircraft. We infer the sum of HO2NO2 andCH3O2NO2 as the difference between <IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img4.gif" ALT="$Sigma$">PN measurementsand gas chromatographic measurements of the two major peroxy acyl nitrates,peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparisonwith NOy 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 NOy are highlytemperature dependent: on average 30% of NOy at 230K, 15% ofNOy at 240K, and <IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-377-img7.gif" ALT="$<$">5% of NOy 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

atmospheric chemistry and physics

Measurements of the sum of HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in the remote troposphere