Effect of Rain Scavenging on Altitudinal Distribution of Soluble Gaseous Pollutants in the Atmosphere

TL;DR

This paper develops a numerical model to analyze how rain scavenging affects the vertical distribution of soluble gaseous pollutants like ammonia and sulfur dioxide in the atmosphere, revealing height-dependent and non-stationary scavenging coefficients.

Contribution

It introduces a non-stationary convective diffusion model for rain scavenging of soluble gases, considering droplet size distribution and initial pollutant profiles, which advances understanding of altitude-dependent scavenging processes.

Findings

Scavenging coefficient varies with height and time during rainfall.

Initial pollutant distribution significantly influences scavenging efficiency.

Scavenging coefficient increases with height initially then decreases in upper layers.

Abstract

We suggest a model of rain scavenging of soluble gaseous pollutants in the atmosphere. It is shown that below-cloud gas scavenging is determined by non-stationary convective diffusion equation with the effective Peclet number. The obtained equation was analyzed numerically in the case of log-normal droplet size distribution. Calculations of scavenging coefficient and the rates of precipitation scavenging are performed for wet removal of ammonia (NH3) and sulfur dioxide (SO2) from the atmosphere. It is shown that scavenging coefficient is non-stationary and height-dependent. It is found also that the scavenging coefficient strongly depends on initial concentration distribution of soluble gaseous pollutants in the atmosphere. It is shown that in the case of linear distribution of the initial concentration of gaseous pollutants whereby the initial concentration of gaseous pollutants decreases with altitude, the scavenging coefficient increases with height in the beginning of rainfall. At the later stage of the rain scavenging coefficient decreases with height in the upper below-cloud layers of the atmosphere.