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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-285
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
04 Apr 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Rainfall drives atmospheric ice nucleating particles in the maritime climate of Southern Norway
Franz Conen1, Sabine Eckhardt2, Hans Gundersen2, Andreas Stohl2, and Karl Espen Yttri2 1Department of Environmental Sciences, University of Basel, Basel, Switzerland
2NILU – Norwegian Institute for Air Research, Kjeller, Norway
Abstract. Ice nucleating particles active at warm temperatures (e.g. −8 °C; INP−8) can transform clouds from liquid to mixed-phase, even at very small number concentrations (< 10 m−3). Over the course of 15 months, we found very similar patterns in weekly concentrations of INP−8 in PM10 (median = 1.7 m−3, maximum = 10.1 m−3) and weekly amounts of rainfall (median = 28 mm, maximum = 153 mm) at Birkenes, southern Norway. Probably, INP−8 were aerosolised locally by the impact of raindrops on plant, litter and soil surfaces. Major snowfall or heavy rain onto snow-covered ground were not mirrored by enhanced numbers of INP−8. Further, source receptor sensitivity fields obtained from transport model calculations for large and small numbers of INP−8 differed more in their likelihood to provide precipitation to southern Norway, than in the proportion of land cover or landuse type. In PM2.5 we found consistently about half as many INP−8 as in PM10. From mid-May to mid- September, INP−8 correlated positively with the fungal markers arabitol and mannitol, suggesting that INP−8 may consist largely of fungal spores. In the future, warmer winters with more rain instead of snow may enhance airborne concentrations of INP−8 during the cold season in southern Norway and in other regions with a similar climate.

Citation: Conen, F., Eckhardt, S., Gundersen, H., Stohl, A., and Yttri, K. E.: Rainfall drives atmospheric ice nucleating particles in the maritime climate of Southern Norway, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-285, in review, 2017.
Franz Conen et al.
Franz Conen et al.
Franz Conen et al.

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Short summary
The first longterm observation of ice nuclei active at −8 °C shows that rainfall drives their abundance throughout all seasons and that they are equally distributed amongst coarse and fine fraction of PM10. Concurrent measurements of fungal markers indicate dominant fungal sources during the warm, but not during the cold season. Snow cover suppresses the aerosolisation of ice nuclei. Changes in snow cover and rainfall are likely to affect atmospheric concentrations of ice nuclei in future.
The first longterm observation of ice nuclei active at −8 °C shows that rainfall drives their...
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