Seasonal variation of airborne coarse and fluorescent particles

Coarse mode aerosols receive relatively little attention in Arctic atmospheric research compared to smaller aerosol populations. However, coarse mode particles have important implications for aerosol-radiation interactions as well as aerosol-cloud interactions, and are hence of climatic relevance. Regarding cloud formation, coarse particles in the Arctic are often composed of sea salt, a very efficient cloud condensation nuclei, and biological particles, which can function as ice nucleating particles (INPs). Here, we present the annual cycle of properties of particles > 500 nm measured with a Wideband Integrated Bioaerosol Sensor (WIBS). The fluorescence signal can be an indication for biological particles and hence a potential population of INPs. We find that during winter (Nov – April) coarse particle number concentrations and diameters are higher than during summer, likely owing to the influence of Arctic haze and blowing snow. Also, the total fluorescence signal is higher, pointing towards a sea spray signature. However, in summer (June/July) the number fraction of fluorescent particles is highest in the 75th percentile and most variable between June and October, suggesting influence from a variety of sporadic sources, which are likely to emit also biological material.