The role of snow in submicron sized aerosol scavenging in thunderstorms

In this research, the impact of collection of aerosol particles (AP) by snow in cumulonimbus clouds was analyzed, with a additional consideration of the collection process caused by electrostatic charging of aerosols and hydrometeors. Aerosols in the atmosphere play a key role in cloud formation, development, products, climate change, environment and public health. Spectral scavenging coefficients for different aerosol-snow interaction processes were calculated, analyzed and implemented in a three-dimensional, three-moment microphysical model. The model explicitly tracks the concentration and mass distribution of aerosols in all categories of hydrometeors. The results show that Brownian and turbulent diffusion are the dominant mechanisms for smaller aerosols, while inertial interception become significant for larger particles. Impaction scavenging is most effective for aerosols with diameters above 0.5 µm, but is neglected for most aerosols injected, as they have diameters less than 0.2 µm. Processes caused by electrostatic charging additionally contribute to the efficiency of aerosol collection. Numerical experiments included two approaches: (1) aerosols were collected only by cloud and rainwater and (2) aerosols were collected by cloud water, rainwater, and snow, with additional consideration of the effect of electrostatics. The results of the simulations indicate that snow contributes to a greater removal of aerosol mass than number, due to more efficient collection of larger particles. As the snow flakes melt, the aerosol removal process continues through raindrops. Electrostatic processes further emphasize the importance of including snow scavenging in aerosol collection models, especially in situations of high atmospheric particle charge.

Acknowledgment:

This research was supported by the Science Fund of the Republic of Serbia, No. 7389, Project Extreme weather events in Serbia - analysis, modelling and impacts” - EXTREMES

Poster: link