Preprints
https://doi.org/10.5194/egusphere-2022-1079
https://doi.org/10.5194/egusphere-2022-1079
 
01 Nov 2022
01 Nov 2022
Status: this preprint is open for discussion.

Late summer transition from a free-tropospheric to boundary layer source of Aitken mode aerosol in the high Arctic

Ruth Price1, Andrea Baccarini2,a, Julia Schmale2, Paul Zieger3,4, Ian M. Brooks1, Paul Field1,5, and Ken S. Carslaw1 Ruth Price et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, UK
  • 2Extreme Environments Research Laboratory, École Polytechnique Fédérale de Lausanne, Sion, Switzerland
  • 3Department of Environmental Science, Stockholm University, Stockholm, Sweden
  • 4Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 5Met Office, Exeter, UK
  • anow at: Laboratory of Atmospheric Processes and their Impacts, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

Abstract. In the Arctic, the aerosol budget plays a particular role in determining the behaviour of clouds, which are important for the surface energy balance and thus for the region’s climate. A key question is the extent to which cloud condensation nuclei in the high Arctic summertime boundary layer are controlled by local emission and formation processes as opposed to transport from outside. Each of these sources is likely to respond differently to future changes in ice cover. Here we use a global model and observations from ship and aircraft field campaigns to understand the source of high Arctic aerosol in late summer. We find that particles formed remotely, i.e. at lower latitudes, outside the Arctic, are the dominant source of boundary layer Aitken mode particles during the sea ice melt period up to the end of August. Particles from such remote sources, entrained into the boundary layer from the free troposphere, account for nucleation and Aitken mode particle concentrations that are otherwise underestimated by the model. This source from outside the high Arctic declines as photochemical rates decrease towards the end of summer, and is largely replaced by local new particle formation driven by iodic acid emitted from the surface and associated with freeze-up. Such a local source is consistent with strong fluctuations in nucleation mode concentrations that occur in September. Our results suggest a high-Arctic aerosol regime shift in late summer, and only after this shift do cloud condensation nuclei become sensitive to local aerosol processes.

Ruth Price et al.

Status: open (until 14 Dec 2022)

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Ruth Price et al.

Model code and software

ruthprice/price-acp-figures: code Ruth Price https://doi.org/10.5281/zenodo.7185175

Ruth Price et al.

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Short summary
Arctic clouds can control how much energy is absorbed by the surface or reflected back to space. Using a computer model of the atmosphere, we investigated the formation of atmospheric particles that allow cloud droplets to form. We found that particles formed aloft are transported to the lowest part of the Arctic atmosphere and that this is a key source of particles. Our results have implications for the way Arctic clouds will behave in the future as climate change continues to impact the region.