TOTAL NITROGEN-DIOXIDE AT THE ARCTIC POLAR CIRCLE SINCE 1990

Daily ground-based NO2 column measurements have been conducted with UV -visible SAOZ diode-array spectrometers at Sodankyla in northern Finla nd since January 1990 and at 3 additional stations during EASOE. Inspe ction of the data indicates: a total NO2 reduction by 30% by the Pinat ubo aerosol in spring and summer 1992 compared to the previous years; a poor correlation in winter with potential vorticity indicative of mo tion of the vortex and of advection of air from mid-latitude, frequent during EASOE; an absence of significant global denitrification by sed imentation of nitric acid on PSC particles inside the vortex; and a hi gh correlation between total NO2 and 30 - 50 hPa temperature. The latt er is unexpected in winter 1991-92, since most of NOx (NO + NO2 + ClON O2 + 2N2O5) at the altitude of the aerosol layer should have been conv erted into liquid nitric acid. This is expected to revert only slowly to NOx at high latitude in winter. The correlation suggests a temperat ure dependent saturation of the aerosol water / sulfuric acid droplets and / or a temperature dependent mechanism of restitution of NOx to t he gas phase.