Year to year variability of stratospheric NO2 (1995 to 2026) above Kiruna, Northern Sweden, derived from ground-based and satellite DOAS observations

Stratospheric NO2 originates from the decomposition of N2O after its transport from the troposphere into the stratosphere. Due to anthropogenic activities the tropospheric mixing ratios of N2O increased from pre-industrial levels of about 265 ppb to about 339 ppb in 2025. Alone during the time of our ground based DOAS measurements the increase of tropospheric N2O was around +9%, which should result in a similar NO2-increase. In order to test this hypothesis we investigated stratospheric NO2 column densities from long-term zenith DOAS measurements (1995 – 2026) in Kiruna (northern Sweden). We also compare the ground-based data to satellite observations from several UV/vis sensors (GOME-1, SCIAMACHY, OMI, GOME-2AB, TROPOMI). Good agreement of the relative temporal variations is found between both data sets, but systematic deviations occur for the absolute values, which can be explained by differences in the solar zenith angles during the measurements and the analysis details. Interestingly, no clear trend in the stratospheric NO2 columns during the whole time series is found, which is in contradiction to the above assumption. Moreover, a strong year-to-year variability of up to about +/-10% is found. Both findings indicate that the stratospheric NO2 amount is influenced by more complex processes, most probably related to variations of the Brewer-Dobson circulation. We investigate such influences by comparing our long term data sets of stratospheric NO2 to variables describing the entry of tropospheric air into the stratosphere and the strength of the Brewer-Dobson circulation.