Stratospheric Nitrogen Dioxide in the Antarctic

Several UV-Visible spectrometers have been developed at the ISAC-CNR Institute. Differential Optical Absorption Spectroscopy (DOAS) methodology is applied to their measurements to monitor the amount of stratospheric trace gases: mainly ozone (O3) and nitrogen dioxide (NO2) deeply involved in the ozone cycle. Observations of the scattered zenith-sky light were performed with this instrumentation at the Terra Nova Bay station (TNB) – Antarctica. The GASCOD (Gas Analyzer Spectrometer Correlating Optical Differences), is briefly described and a method for data analysis and validation of the results is introduced. Some aspects of the DOAS technique are presented: the algorithm allowing the best spectral alignment between spectra obtained with GASCOD and a high-resolution wavelength calibrated spectrum, is explained. Simple considerations allow for the calculation of the NO2 concentration in the background spectrum used in DOAS analysis. For the period of activity of the GASCOD at TNB (1996-2003), the results of NO2 vertical column density (VCD) at twilight show the maximum in the summer and the minimum during the winter. Three years of measurements (2001-2003) are analyzed in terms of stratospheric temperature and Potential Vorticity, to have information about the stratospheric warming occurred in 2002 over Antarctica. The correlation between NO2 atmospheric contents and stratospheric temperature is highlighted. The diurnal variations of NO2, which are controlled by the photochemistry, show a particular behaviour at high latitudes. The analysis of the AM/PM ratios - the sunrise NO2 VC (AM) over the sunset VC (PM) - at different seasons and various Solar Zenith Angles (SZA) are presented and discussed.