Total column densities of tropospheric and stratospheric trace gases in the undisturbed Arctic summer atmosphere

Ground-based FTIR measurements have been performed in the Arctic summer in July 1993 and June 1994 at 79° N to study the zenith column densities of several trace gases in the undisturbed Arctic summer atmosphere. Zenith column densities of H₂O, N₂O, HNO₃, NO₂, NO, ClONO₂, ClO, HCl, HF, COF₂, OCS, SF₆, HCN, CH₄, C₂H₆, C₂H₂, CO, O₃, CFC-12, CFC-22, and CO₂ were retrieved by line-by-line calculations. The results are compared with winter and springtime observations measured at the same site, with column densities obtained in the Antarctic summer atmosphere, and with measurements at midlatitudes. For HCl the spectra give lower total zenith columns than expected, but the ratio HF/HCl agrees well with midlatitude literature data. Measurements of ClONO₂ give low total columns in agreement with observations at midlatitudes. In the undisturbed atmosphere HCl was found to be in excess of ClONO₂. The total columns of HNO₃, N₂O and the sum of NO and NO₂ agree with summer observations in Antarctica. Results for the tropospheric trace gas C₂H₆ are higher by 250% when compared with Antarctic observations. Contrary to N₂O and CH₄ the seasonal cycle of C₂H₆ and C₂H₂ give much higher total columns in winter/spring compared to the summer observations. This is assigned to transport of polluted airmasses from mid-latitudes into the Arctic.