Stability effects on aerosol size and height distributions

Abstract

The usual description of the vertical distribution of aerosol concentrations assumes neutral atmospheric stratification. This work examines the influence of atmospheric stability on vertical aerosol concentration profile. A model is developed to describe the aerosol transport in the atmospheric surface layer. The model describes a balance between upward aerosol flux due to atmospheric turbulence and downward flux due to gravitational deposition. Monin-Obukhov similarity theory describes the turbulent profiles of wind, temperature and specific humidity. An approximate equilibrium expression relates particle size to ambient relative humidity. To isolate the role of transport and growth, we first use the model to describe the surface layer concentration of inert particles unaffected by relative humidity. The calculations show that growth phenomena must be included to correctly describe aerosol concentrations in the presence of relative humidity gradients. Complete calculations of aerosols concentrations, including growth effects, show that the concentration of large particles (radius greater than 5 ?m) can vary by an order of magnitude depending on stability. With light winds, the stability effect on large aerosols substantially affects the slope of the expected aerosol size distribution. With strong winds the aerosol distribution is not affected by changes in temperature and humidity lapse rates, but instead is governed by wind-shear-produced turbulent mixing. DOI: 10.1111/j.2153-3490.1980.tb00951.x