Spatial distribution of aerosols in the Inn Valley atmosphere during wintertime

This study analyzes the structure of the wintertime boundary layer in an Alpine valley (Inn Valley, Austria) for a case of high air pollution. We present airborne aerosol observations collected with particle counters and a backscatter lidar. The effect of upslope winds on the spatial distribution of pollutants is investigated. An asymmetry in the aerosol distribution is observed in the cross-valley direction which presumably is related to differences in orientation and albedo of the two valley slopes. A one-sided thermal circulation, which develops above the sun-exposed slope, is most likely responsible for the observed redistribution of aerosols during daytime. Elevated aerosol layers form at the height of shallow inversion layers. Despite this vertical transport of pollutants by slope winds, no effective vertical venting of the polluted air mass into the free atmosphere can be achieved.