Fluorescent aerosols in the Arctic: Seasonality and sources

Aerosol-cloud interactions play an important role in regulating the Arctic climate. However, cloud formation processes in the Arctic remain poorly understood and information on aerosol properties in this environment are insufficient, especially during polar night (Schmale et al., 2021). Ice nucleating particles (INPs) contribute to the formation of ice crystals in clouds at temperatures above -38 °C (Kanji et al., 2017), for example in mixed phase clouds, i.e. clouds with liquid droplets and ice crystals, which are predominant in the Arctic. Therefore, the study of INP sources in the Arctic is crucial. One potential source of INPs are biological particles. They can be long-range transported or be emitted from local sources, such as blowing snow events, ice-free open ocean, open leads or melt ponds. Importantly, the future warmer Arctic will potentially have more melt ponds over a longer period in summer and more open water, hence the source strength of biological particles might change in the future. Therefore, it is important to understand the sources and processes of biological particles and their relation to INPs. Biological aerosols are difficult to measure directly. One method is through their fluorescent properties. Here we present first results of one year of fluorescent particle data, measured in the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) by a Wideband Integrated Bioaerosol Sensor (WIBS-NEO). We describe the seasonal cycle of fluorescent aerosols. Figure 1 shows that median fluorescent particle number concentrations peak in January, which is consistent with the onset of Arctic haze. The highest number concentrations were observed in summer, which could be an indicator of higher abundance of biological aerosols from local sources. We relate the data to potential biogenic sources, such as plankton or bacteria. Furthermore, we investigate potential weather-related processes leading to the presence of fluorescent particles, such as blowing snow events, which occurred frequently in winter. Finally, we will investigate correlations between fluorescent particles and INP concentrations. Importantly, not all fluorescent particles are necessarily biological particles. This study may improve our knowledge of the relation between fluorescent aerosols and biogenic INP abundance in the Arctic, meaning that INP number concentrations could potentially be derived from automated and high time resolution measurements, such as from the WIBS.