AerSett v1.0: a simple and straightforward model for the settling speed of big spherical atmospheric aerosols

Abstract

This study introduces AerSett v1.0 (AERosol SETTling version 1.0), a model giving the settling speed of big spherical aerosols in the atmosphere without going through an iterative equation resolution. We prove that, for all spherical atmospheric aerosols with diameter D up to 1000 µm, this direct and explicit method including the drag coefficient formulation of Clift and Gauvin (1971) and the Davies (1945) slip correction factor gives results within 2 % of the exact solution obtained from the numerical resolution of a non-linear fixed-point equation. This error is acceptable considering the uncertainties on the drag coefficient formulations themselves. For D<100 µm, the error is below 0.5 %. We provide a Fortran implementation of this simple and straightforward model, hoping that more chemistry–transport models (CTMs) and general circulation models will be able to take into account large-particle drag correction to the settling speed of big spherical aerosol particles in the atmosphere, without performing an iterative and time-consuming calculation.