Characteristics of natural Arctic aerosols emitted from a wide range of local sources during ARTofMELT2023

The Arctic has been experiencing a rise in ambient temperature several times higher than the global average. This warming trend has led to a continuous decline in sea ice coverage and snowpack prevalence. Aerosol sources, such as those from the open ocean and tundra, have become more prevalent throughout the year. These sources emit primary biological aerosol particles (bioaerosols) some of which exhibit ice nucleating properties at high temperatures (>-15C). Ice nucleating particles (INPs) play a crucial role in cloud ice formation, affecting cloud physical and optical properties, as well as their lifetime. Consequently, this has a substantial impact on the Arctic climate. During the ARTofMELT2023 expedition (Atmospheric Rivers and the Onset of Sea Ice Melt 2023) conducted aboard the Swedish icebreaker Oden in the Atlantic sector of the Arctic Ocean, we assessed the relative importance of several natural bioaerosol sources, such as sea ice, snow melt (to simulate melt ponds) and bulk ocean water. This involved several sea spray simulation chamber and nebulizer experiments, referred to as source experiments. The aerosol particles generated in the 61 source experiments conducted were analyzed using single-particle ultraviolet fluorescence spectroscopy along with other complementary aerosol measurements. These included particle size, black carbon content, particle chemical composition, as well as the microbial community and INP concentration of emitted particles. Additionally, filter samples were obtained for transmission electron microscopy (TEM) analysis. Our findings indicate that sea ice and snow melt are more significant sources of bioaerosols compared to the bulk ocean water, including the sea surface microlayer, indicating the potential importance of melt ponds as a local Arctic bioaerosol source. Furthermore, we found significant differences in the chemical composition, black carbon content and size distribution of the various analyzed aerosol sources.