In situ measurements of HNO3, NOy, NO, and O3 in the lower stratosphere and upper troposphere

In situ measurements of nitric acid (HNO3), reactive nitrogen (NOgamma), nitric oxide (NO), and ozone (O-3) made in the upper troposphere (UT) and lower stratosphere (LS) between 29 degrees and 33 degreesN latitudes during September 1999 are used to examine NOgamma partitioning and correlations between the measured species in these regions. The fast-response (1 s) HNO3 measurements are acquired with a new autonomous CIMS instrument. In the LS, HNO3 accounts for the majority of NOgamma and the sum of HNO3 and NOx accounts for approximately 90% of NOgamma. In the UT, the sum of HNO3 and NOx varies between 40% and 100% of NOgamma. Both HNO3 and NOgamma are strongly positively correlated with O-3, with larger correlation slopes in the UT than in the LS. In the UT at low values of the quantity (NOgamma-NOx-HNO3) it is uncorrelated with O-3, while at higher values, a positive correlation with O-3 is found. Of these two air mass types, those with higher (NOgamma NOx-HNO3) mixing ratios are likely associated with the presence of peroxyacetyl nitrate (PAN) that is produced by NOx-hydrocarbon chemistry. (C) 2001 Elsevier Science Ltd. All rights reserved.