| Concentrations of nitric acid (HNO3), nitrous oxide (N 2O), and total reactive nitrogen (NOy) in the Antarctic lower stratosphere are studied. The work uses measurements obtained during 1993 and 1995 by a ground-based millimeter-wave spectrometer (GBMS), operating at the South Pole, and by instruments aboard the UARS and SPOT-3 satellites, complemented by results from a photochemical box model.; The first part of this research consists of a first-time intercomparison between the two longest records of gas-phase HNO3 vertical profiles in the Antarctic stratosphere. Such a comparison shows extremely good agreement during most seasons of 1993 and 1995 between measurements by the GBMS and the newly-released version 5 HNO3 data from the Microwave Limb Sounder (MLS) aboard UARS. In this analysis, I confined comparisons to MLS data in the 70–80° S latitude band. Further selection of data was made by trajectory matching to limit comparisons to air parcels observed by the GBMS during their passage over the Pole. Where differences between the two sets of HNO3 profiles occur, I find that, for the most part, they are correlated to periods of strong inhomogeneity in the HNO3 horizontal distribution over the Antarctic region, suggesting that they are mainly due to the lack of co-location between the two data sets, and not to true instrumental or retrieval biases.; In the second part of this study, I estimate NOy mixing ratio profiles over the same time and vertical ranges encompassed by the HNO 3 comparison. The derived NOy values are then correlated to GBMS N2O measurements. The estimation of NOy involves the use of measurements of HNO3 by the GBMS, NO and NO2 by the Halogen Occulatation Experiment (HALOE) aboard UARS, NO2 by the Polar Ozone and Aerosol Measurements II (POAM II) instrument aboard SPOT-3, and calculations of minor NOy constituents such as N 2O5, ClONO2, and HO2NO2 from a photochemical box model. Satellite data to be used for NOy calculations were constrained to a northernmost latitude limit of 60°S, and a further selection of satellite data was performed by the same trajectory matching technique adopted in the first part of the work.; Results for the fall season show that the NOy column density (covering the range ∼14–33 km) is about 20% larger than that measured outside the polar vortex in previous studies. (Abstract shortened by UMI.)... |
