FT-IR spectrometers are capable to quantifiy the total column amounts of many important trace gases in the troposphere and stratosphere. At present the following species are retrieved from the Kiruna data: O3 (ozone), ClONO2, HNO3, HCl, CFC-11, CFC-12, CFC-22, NO2, N2O, NO, HF, C2H2, C2H4, C2H6, CH4, CO, COF2, H2O, HCN, HO2NO2, NH3, N2, and OCS Selected research topics and activities: chemical ozone depletion by observation of key species (O3, ClONO2, HNO3, HCl, ..) details of the ozone formation process by isotopic studies in ozone profile retrieval to detect dynamical changes transport studies of chemical tracers and tropospheric pollutants satellite validation
The ground-based infrared spectrometer records spectra in the middle infrared by looking through the atmosphere directly into the sun or the moon. This requires cloud free observation conditions. The homosphere or lower atmosphere from ground to about 100 km altitude contains more than 99 % of all atmospheric molecules. These molecules are overwhelmingly in their ground states, but have typically a fair number of unoccupied excited rotational and vibrational states that can be occupied by absorbing discrete energy amounts that are given by their molecular spectroscopic properties. These energies typically correspond to photon energies found in the infrared. Thus, each molecular species leaves a characteristic fingerprint of absorption lines in the solar spectrum recorded at ground-level, by which it can be detected and identified. The energy taken up by the molecules is mostly transferred into heat, when returning into the ground state. The strength of an absorption feature increases almost linear over a wide range with the total number of molecules in the optical line of sight and is thus a measure for the total number of molecules. The data analysis is performed by comparing the recorded spectrum to a computer simulated model atmosphere with absorption features calculated from a spectroscopic data base (e.g. HITRAN96). The results reported are total column amounts, which are the total number of molecules above the observer for a given species over an area of 1 cm² for zenith geometry (integration over altitude across the atmosphere along an earth radial path). However, due to pressure broadening, which is dominant in the troposphere, and due to Doppler broadening, which is dominant in the upper stratosphere, there is also information on the vertical distribution of a trace gas in its observed line shape. Profile retrieval is a current topic of research, but the information is roughly limited to the altitude range from 10 to 35 km altitude.
The FT-IR spectrometer is operated by IRF Kiruna in collaboration with: Institut für Meteorologie und Klimaforschung, Germany, and the Solar Terrestrial Environment Laboratory, Japan.
Network for the Detection of Stratospheric Changes (NDSC) The NDSC is a major component of the international upper atmosphere research effort and has been endorsed by national and international scientific agencies, including the International Ozone Commission, the United Nations Environment Programme (UNEP), and the World Meteorological Organization (WMO).