Scavenging coefficients, A, for the removal of HNO3 vapor from the atmosphere by both cloud and rain drops have been calculated for assumed models of drop-size distribution. For cumulus clouds a value of 0.2 s-1 is estimated for A. Evaluation of rainfall washout coefficients gives values of A ranging from 1.3 × 10-5 to 1.5 × 10-3 s-1, depending upon the rainfall rate, upon the drop-size distribution function employed, and, strongly upon the lower limit of the raindrop size employed in the calculations. The concentration of soluble gas dissolved within a falling drop per unit fall distance is found to be a function of drop size, with the smaller drops accumulating the greater concentration. The long-term average rate of heterogeneous removal of HNO3 is estimated in the range 1 - 8 × 10-6 s-1, representing comparable contributions from dry deposition and rainfall scavenging.
This page was last updated 2010-06-03.
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