Measurements of the sum of HO 2 NO 2 and CH 3 O 2 NO 2 in the remote troposphere

• Main Authors: J. G. Murphy, J. A. Thornton, P. J. Wooldridge, D. A. Day, R. S. Rosen, C. Cantrell, R. E. Shetter, B. Lefer, R. C. Cohen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2004
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Tropospheric Ozone Production About the Spring Equinox
• Online Access: https://doaj.org/article/406e6c71dd5e445c9a560d8ee2d96213

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 240K, 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 230K, 15% of NO y at 240K, and 5% of NO y 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 -5 s -1 ) agreed with the observed sum of HO 2 NO 2 +CH 3 O 2 NO 2 to better than 35% below 240K where the concentration of these species is largest.