Determination of the stratospheric NO2 slant column by means of GASCOD type instrument at Stara Zagora station

Summary form only given. NO₂ is a member of the nitrogen oxides family which takes part in a large number of homogeneous chemical and photochemical reactions. They are very important for the distribution of the stratospheric ozone and the ozone decline. So, it is clear that NO₂ plays a significant role in understanding the climate change processes. The study of the photochemistry and transport phenomena of NO₂ requires long-time measurements. For some years at Mt.Cimone station near Bologna, Italy, a UV-VIS spectrometer, GASCOD has operated, developed at the Institute for Atmospheric and Oceanic Sciences (ISAO) for detection of atmospheric trace gases-ozone, NO₂ etc. Since August 1999 a similar instrument, developed by the ISAO too, has been installed at the observatory in Stara Zagora (42°25´N, 25°38´E), Bulgaria, at the Department of the Solar-Terrestrial Influences Laboratory for diurnal and long-time studies, simultaneously at Mt.Cimone and Stara Zagora. The Stara Zagora GASCOD type instrument is placed on the roof of one of the observatory buildings and the diffused zenith skylight by means of a 45° mirror is directed to the spectrometer and by the help of a f/5 telescope it is focused on the entrance slit. The instrument records the spectra in the range of 410 nm to 460 nm. DOAS methodology is applied for retrieving the NO₂ slant column. The preliminary results are shown and a comparison is made between the measurements carried out at Mt.Cimone station and Stara Zagora station