Effect of rain scavenging on altitudinal distribution of soluble gaseous pollutants in the atmosphere

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 (NH 3 ) and sulfur dioxide (SO 2 ) 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.

Airborne measurements of gas and particle pollutants during CAREBeijing-2008

“…For example, there was moderate rain due to a thunderstorm on 27 August (www.wunderground.com). The wet deposition helps scavenge the aged particles (Nilsson, et al, 2001;Elperin et al, 2011). Fresh emission from vehicles was observed, consistent with the results of Wang et al (2011).…”

The washout effects of rainfall on atmospheric particulate pollution in two Chinese cities

“…Rainfall is recognized as one of the main natural processes to improve air quality (Duhanyan and Roustan, 2011;Elperin et al, 2011), and it can greatly enhance the positive reductions achieved by anthropogenic control measures (Leung and Gustafson, 2005). Our previous study assessed the rainfall removal efficiency for total suspended particles (TSP) and found that artificial rain interventions may worsen air quality due to the lower removal of TSP without rainfall (Guo et al, 2014).…”

Wet precipitation scavenging of soluble atmospheric trace gases due to chemical absorption in inhomogeneous atmosphere

“…In our previous studies (see, e.g. Elperin et al 2011;Baklanov et al 2013) we showed that accounting for the droplet size distribution does not lead to significant changes in the rate of gas scavenging in comparison with that calculated using the average radius approximation. Therefore, in the present study we performed calculations for the monosize droplets having the average rain droplet radius.…”

“…Equation of mass balance for soluble trace gas in the gaseous and liquid phases reads (Elperin et al 2011):…”