What is the contribution of bioaerosols to the atmospheric burden of cloud ice nucleating particles?

Daniel O'Sullivan, Mike Adams, Jesus Vergara Temprado, Thomas Whale, Mark Tarn, Grace Porter, Mark Holden, Benjamin John Murray, M.E. Webb

In the absence of particles, pure cloud-sized water droplets will supercool down to about -37°C. However, atmospheric aerosols can catalyse (nucleate) the formation of cloud ice at temperatures much warmer than this. Recent laboratory and field studies have demonstrated that mineral dusts and marine sea spray aerosols contain effective ice nucleating sites, whose activity becomes important for clouds at temperatures below about -20°C. However, clouds are frequently observed to glaciate at temperatures warmer than this, and it is unclear which nucleating particles are responsible for these observations. Past studies have suggested that bioaerosol particles might be a substantial source of efficient INPs active in this temperature regime, yet our understanding of the sources and even the types of bioaerosols which can perform this role is poorly known. In this work, results from both lab and field studies examining the characteristics and abundances of biogenic ice nucleating particles are presented. We demonstrate that extracellular proteins produced by Fusarium fungi exhibit potent ice nucleating activity and confer ice nucleating activities to soil dusts if the fungus is present. We further examine the ultimate roles which biologically derived particles play in determining the ice nucleating abilities of ambient aerosols sampled within the UK.

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