ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11319-2012 Vertical transport of pollutants by shallow cumuli from large eddy simulations Chen G. 1 Xue H. 1 Feingold G. 2 Zhou X. 1 3 Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, 100871, China NOAA Earth System Research Laboratory, Boulder, CO 80305, USA Chinese Academy of Meteorological Sciences, Beijing, 100081, China 03 12 2012 12 23 11319 11327 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/11319/2012/acp-12-11319-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11319/2012/acp-12-11319-2012.pdf

This study investigates the vertical transport of a passive tracer in a shallow cumulus boundary layer using large eddy simulations. The tracer source is at the surface in one case, and in the inversion layer in the other case. Results show that shallow cumulus clouds can significantly enhance vertical transport of the tracer in both cases. In the case with surface-borne pollutants, cloudy regions are responsible for the upward transport, due to the intense updrafts in cumulus clouds. In the case where pollutants are aloft, cloud-free regions are responsible for the downward transport, but the downward transport mainly occurs in thin regions around cloud edges. This is consistent with previous aircraft measurements of downdrafts around cumulus clouds and indicates that the downward transport is also cloud-induced. Cumulus convection is therefore able to both vent pollutants upward from the surface and fumigate pollutants in the inversion layer downward into the lower boundary layer.

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