A Comparison of NOy Budgets from the NOAA P3 during SOS99 and TexAQS 2000

During SOS99 and TexAQS 2000, the NOAA WP-3D aircraft sampled air from: Nashville, Atlanta, Chicago, Houston, Dallas, and the Houston Ship Channel. Continuous, high time resolution (< 2 s) measurements were performed of NO, NO2, NOy, and HNO3. PAN, MPAN, and PPAN were also measured with a time resolution of approximately 20 s every 2 to 5 minutes. In this work we examine the speciated NOy budgets for both years' missions and investigate systematic differences in nitrogen oxide chemistry in each of the individual urban areas . In addition, this analysis provides a quality check of the measurements. Determination of an air mass from an individual city was made by analysis of CO levels and wind direction, as well as with HYSPLIT trajectory modeling. For both missions and each urban area the sum of the individual nitrogen oxide species comprised more than 90% of the NOy measurement on average. These results strongly indicate that most of the NOy budget is accounted for by NOx, nitric acid and PAN type compounds. The ratio of HNO3 to NOy-NOx (NOz) was also evaluated for each location in order to provide a higher spatial resolution evaluation of the NOy budget. This ratio was found to be on average the largest in Nashville (.84) and Dallas (.72) and the lowest in Houston (.55) and the Houston Ship Channel (.50). These data suggest that either PAN formation or nitric acid deposition is more efficient in the Houston area. We believe the former conclusion is more plausible and is consistent with the rapid ozone production and high levels of reactive hydrocarbons observed in this region.