ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-377-2004 Measurements of the sum of HO<sub>2</sub>NO<sub>2</sub> and CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub> in the remote troposphere Murphy J. G. 1 Thornton J. A. 1 5 Wooldridge P. J. 1 Day D. A. 1 Rosen R. S. 1 Cantrell C. 2 Shetter R. E. 2 Lefer B. 2 Cohen R. C. 1 3 4 University of California at Berkeley, Department of Chemistry, Berkeley, CA, USA National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO, USA University of California at Berkeley, Department of Earth and Planetary Science, Berkeley, CA, USA Lawrence Berkeley National Laboratory, Division of Energy and Environment Technologies, Berkeley, CA, USA now at: University of Toronto, Department of Chemistry, Toronto, ON, Canada 27 02 2004 4 2 377 384 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/377/2004/acp-4-377-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/377/2004/acp-4-377-2004.pdf

The chemistry of peroxynitric acid (HO<sub>2</sub>NO<sub>2</sub>) and methyl peroxynitrate (CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub>)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 240K, we calculate that about 20% of NO<sub>y</sub> in the mid- and high-latitude upper troposphere is HO<sub>2</sub>NO<sub>2</sub>. Under these conditions, the reaction of OH with HO<sub>2</sub>NO<sub>2</sub> 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 (<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="$equiv$"> HO<sub>2</sub>NO<sub>2</sub>+CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub>+PAN+PPN+...) aboard the NCAR C-130 research aircraft. We infer the sum of HO<sub>2</sub>NO<sub>2</sub> and CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub> as the difference between <IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img4.gif" ALT="$Sigma$">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<sub>y</sub> and other nitrogen oxide measurements confirms the importance of HO<sub>2</sub>NO<sub>2</sub> and CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub> 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<sub>2</sub>NO<sub>2</sub>+CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub>) to NO<sub>y</sub> are highly temperature dependent: on average 30% of NO<sub>y</sub> at 230K, 15% of NO<sub>y</sub> at 240K, and <IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-377-img7.gif" ALT="$&lt;$">5% of NO<sub>y</sub> above 250K. 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=1x10<sup>-5</sup>s<sup>-1</sup>) agreed with the observed sum of HO<sub>2</sub>NO<sub>2</sub>+CH<sub>3</sub>O<sub>2</sub>NO<sub>2</sub> to better than 35% below 240K where the concentration of these species is largest.