Calculation of the depletion of airborne pollutant plumes through dry deposition processes

The depletion of airborne pollutant plumes resulting from dry deposition on ground surfaces should be taken into account when estimating pollutant concentrations in air at distances downwind from their sources. This can be done by using a reduced release rate instead of the actual release rate for the pollutant in atmospheric dispersion equations. The reduced release rate is the actual rate of release multiplied by a depletion fraction. Depletion fractions for use with the Gaussian atmospheric dispersion equation of Pasquill and Gifford were calculated by numerical integration for downwind distances ranging from 35 to 90 000 m for release heights from 1 to 400 m, and they are tabulated for convenient interpolation for intermediate values of distance and release height. Pasquill atmospheric stability categories A-G are included. The listed values are for a deposition velocity of 0.01 m/s and a wind speed of 1 m/s but can be easily converted to apply to other deposition velocities and wind speeds. The tabulated values may be applied for downwind distances close enough to the point of release that the Gaussian model may be assumed to be realistic and where the vertical dispersion of the plume has not yet been significantly affected by the overlying atmospheric lid.