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 amounts of stratospheric trace gases: mainly ozone (O-3) and nitrogen dioxide (NO2) which is involved in the ozone cycle. Observations of the scattered zenith-sky light were performed with one of these instruments installed at the Terra Nova Bay station (TNB), Antarctica. GASCOD (Gas Analyzer Spectrometer Correlating Optical Differences) is described briefly and a method for data analysis and validation of the results 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 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 a maximum in the summer and a minimum in the winter. Three years of measurements (2001-2003) are analysed in terms of stratospheric temperature and potential vorticity to obtain information about stratospheric warming that occurred in 2002 over Antarctica. The correlation between NO2 atmospheric content and stratospheric temperature is highlighted. The diurnal variations of NO2, which are controlled by photochemistry, show an unusual behaviour at high latitudes. Analysis of the a.m./p.m. ratios-the sunrise NO2 VC (a.m.) over the sunset VC (p.m.)-during different seasons and at various Solar Zenith Angles (SZA) is presented and discussed

Perspectives of 2D and 3D mapping of atmospheric pollutants over urban areas by means of airborne DOAS spectrometers

tants, offering numerous advantages over conventional networks of in situ analysers. We propose some innovative solutions in the field of DOAS (Differential Optical Absorption Spectroscopy) remote systems, utilizing diffuse solar light as the radiation source. We examine the numerous potentialities of minor gas slant column calculations, applying the «off-axis» methodology for collecting the diffuse solar radiation. One of these particular approaches, using measurements along horizontal paths, has already been tested with the spectrometer installed on board the Geophysica aircraft during stratospheric flights up to altitudes of 20 km. The theoretical basis of these new measurement techniques using DOAS remote sensing systems are delineated to assess whether low altitude flights can provide 2D and 3D pollution tomography over metropolitan areas. The 2D or 3D trace gas total column mapping could be used to investigate: i) transport and dispersion phenomena of air pollution, ii) photochemical process rates, iii) gas plume tomography, iv) minor gas vertical profiles into the Planetary Boundary Layer and v) minor gas flux divergence over a large area