Inferring ozone production in an urban atmosphere using measurements of peroxynitric acid

K. M. Spencer, D. C. McCabe, J. D. Crounse, J. R. Olson, J. H. Crawford, A. J. Weinheimer, D. J. Knapp, D. D. Montzka, C. A. Cantrell, R. S. Hornbrook, R. L. Mauldin III, P. O. Wennberg
2009 Atmospheric Chemistry and Physics  
Observations of peroxynitric acid (HO 2 NO 2 ) obtained simultaneously with those of NO and NO 2 provide a sensitive measure of the ozone photochemical production rate. We illustrate this technique for constraining the ozone production rate with observations obtained from the NCAR C-130 aircraft platform during the Megacity Initiative: Local and Global Research Observations (MILAGRO) intensive in Mexico during the spring of 2006. Sensitive and selective measurements of HO 2 NO 2 were made in
more » ... O 2 were made in situ using chemical ionization mass spectrometry (CIMS). Observations were compared to modeled HO 2 NO 2 concentrations obtained from the NASA Langley highly-constrained photochemical time-dependent box model. The median observedto-calculated ratio of HO 2 NO 2 is 1.18. At NO x levels greater than 15 ppbv, the photochemical box model underpredicts observations with an observed-to-calculated ratio of HO 2 NO 2 of 1.57. As a result, we find that at high NO x , the ozone production rate calculated using measured HO 2 NO 2 is faster than predicted using accepted photochemistry. Inclusion of an additional HO x source from the reaction of excited state NO 2 with H 2 O or reduction in the rate constant of the reaction of OH with NO 2 improves the agreement. Correspondence to: K. M. Spencer (kspencer@caltech.edu) The relative importance of the HO 2 NO 2 sinks depends on temperature, pressure, OH radical concentration, and the Published by Copernicus Publications on behalf of the European Geosciences Union.
doi:10.5194/acp-9-3697-2009 fatcat:yroasi7n4rbprhqy7axxpk25ga