A parameterization of size resolved below cloud scavenging of aerosols by rain J. S. Henzing1, D. J. L. Olivié2, and P. F. J. van Velthoven1 1Royal Netherlands Meteorological Institute KNMI, De Bilt, The Netherlands 2Meteo France, CNRM, Toulouse, France
Abstract. A size dependent parameterization for the removal of aerosol particles by
falling rain droplets is developed. Scavenging coefficients are calculated
explicitly as a function of aerosol particle size and precipitation
intensity including the full interaction of rain droplet size distribution
and aerosol particles. The actual parameterization is a simple and accurate
three-parameter fit through these pre-calculated scavenging coefficients.
The parameterization is applied in the global chemistry transport model TM4
and the importance of below-cloud scavenging relative to other removal
mechanisms is investigated for sea salt aerosol. For a full year run (year
2000), we find that below-cloud scavenging accounts for 12% of the total
removal of super-micron aerosol. At mid-latitudes of both hemispheres the
fractional contribution of below-cloud scavenging to the total removal of
super-micron sea salt is about 30% with regional maxima exceeding 50%.
Below-cloud scavenging reduces the global average super-micron aerosol
lifetime from 2.47 to 2.16 days in our simulations. Despite large
uncertainties in precipitation, relative humidity, and water uptake by
aerosol particles, we conclude that below cloud scavenging is likely an
important sink for super-micron sized sea salt aerosol particles that needs
to be included in size-resolved aerosol models.
Citation: Henzing, J. S., Olivié, D. J. L., and van Velthoven, P. F. J.: A parameterization of size resolved below cloud scavenging of aerosols by rain, Atmos. Chem. Phys., 6, 3363-3375, doi:10.5194/acp-6-3363-2006, 2006.