Intercomparison and validation of FTIR measurements with the Sun, the Moon and emission in the Arctic

During the last three years we performed FTIR measurements of the polar atmosphere with the Sun or the Moon as a radiation source or in emission. The measurements have been made at the NDSC station (Network for the detection of stratospheric changes) in Ny-Alesund (79°N, 11°E) with commercially available, uncooled instruments. We retrieved the column densities of trace gases from the absorption spectra. The emission spectra have been analysed using the equivalent width method for the derivation of the column amounts of the trace gases. Aerosols are included in the simulation. We derived the column amounts of several trace gases including tropospheric (H2O) and stratospheric ones (HNO3, O3). The intercomparison between the results of emission measurements and independent ones (sonde-data and absorption spectra) revealed an average agreement for ozone of about 16%, whereas it is difficult to draw some conclusions for H2O due to larger atmospheric fluctuations. We compared the column amounts of nitric acid derived by the three methods. The Sun and emission data are in a good agreement, whereas the results derived from Moon absorption spectra slightly seem to overestimate the nitric acid and chlorine nitrate column amount.