High Arctic troposphere is cleaner in the summer than the winter?

GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L16805, 6 PP., 2011, doi:10.1029/2011GL048221

 The role of scavenging in the seasonal transport of black carbon and sulfate to the Arctic

Key Points

• Arctic aerosol have a strong seasonal cycle that is dominated by wet scavenging


• Both soot and sulfate are affected nearly equally by wet scavenging processes


• We can anticipate from this study that a warmer Arctic will be a cleaner Arctic

Timothy J. Garrett, Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah, USA

Sara Brattström, Meteorologiska Institutionen, Stockholms Universitet, Stockholm, Sweden

Sangeeta Sharma, Environment Canada, Toronto, Ontario, Canada

Douglas E. J. Worthy, Environment Canada, Toronto, Ontario, Canada

Paul Novelli, GMD, ESRL, Boulder, Colorado, USA

In a prior study, a decade-long dataset of ground-based aerosol and carbon monoxide measurements from Barrow, Alaska (71°N, 157°W) was used to show that surface air in the Arctic is clean during the summer, less due to inhibited transport of pollutants from mid-latitudes, and more because of efficient wet scavenging at temperatures near freezing. Here, the analysis is extended to light-absorbing aerosols, such as black carbon, and to measurements from Alert, Canada (82°N, 62°W). The data imply that both light scattering and light absorbing aerosols have similar seasonal cycles, independent of location, and they are controlled nearly equally by wet scavenging. Removal is particularly efficient at high relative humidities and warm temperatures, which suggests that a future warmer and wetter Arctic may also be cleaner. Assuming aerosol pollutants generally have a warming effect in the Arctic, such an increase in wet scavenging would represent a negative Arctic climate feedback.

Citation: Garrett, T. J., S. Brattström, S. Sharma, D. E. J. Worthy, and P. Novelli (2011), The role of scavenging in the seasonal transport of black carbon and sulfate to the Arctic, Geophys. Res. Lett., 38, L16805, doi:10.1029/2011GL048221.

This recent paper uses aerosol and temperature measurements from Barrow and Alert to show that warmer, wetter summers cause the air at high latitudes to be cleaner in the summer than the winter. No quite what I expected, I'll have to look into this further.