Inferring ozone production in an urban atmosphere using measurements of peroxynitric acid
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
... 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 (firstname.lastname@example.org) 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.