Fluorescent aerosol particles in the Finnish sub-Arctic during the Pallas Cloud Experiment 2022 campaign

Fluorescent aerosol particles (FAPs), as a fraction of total aerosol particles (TAPs), were measured online with a Wideband Integrated Bioaerosol Sensor 5/NEO (WIBS, Droplet Measurement Technologies) from mid-September to mid-December during the Pallas Cloud Experiment 2022 (PaCE22) at the station of Sammaltunturi, located in the sub-Arctic region of Finnish Lapland. The WIBS measures particle size distributions from 0.5 to 30 mu m and fluorescence in three channels of single aerosol particles, as well as particle concentrations. Since biological aerosol particles can exhibit intrinsic fluorescence, FAP concentration can be used as a proxy for primary biological aerosol particles (PBAPs) like bacteria, fungal spores and pollen. The concentrations and size distributions of different fluorescent particles, together with meteorological data and air mass trajectories, allow valuable insights into the emission of PBAPs from northern boreal forests and their dynamic in the atmosphere. We found a clear seasonal trend for most FAP types and a strong, sudden decrease in concentration after the surrounding ground is covered in snow. Caution should be taken in interpreting the data as interference may be introduced by non-biological fluorescent particles like secondary organic aerosols or soot, as well as biological secondary organic aerosols.