Despite the fine weather across Switzerland this week, many observers have noted the poor sky visibility and startling red sunsets. These are the effects of two atmospheric constituents that visited us from far away locations. Our first visitor arrived last weekend and stayed around for a few days: wildfire emissions from Canada. This event was discussed in detail on the excellent MeteoSwiss blog (in German). Yesterday the upper-level airflow shifted to the southwest bringing a more familiar visitor: Saharan dust. Both events were captured well by the ACTRIS-Switzerland measurements performed on the Jungfraujoch. The image plots on this page show the size distributions of aerosol particles weighted by both number and volume (further details described here). The Canadian wildfire and Saharan dust particles are both clearly visible as yellow-to-red blobs in the volume size distribution image. These were the particles responsible for the hazy views around Switzerland. In between the the two major events the aerosol number size distributions show an interesting new particle formation and growth event. Although numerous, these particles were too small to scatter light effectively and impact visibility.
