Influence of electric charges on the washout efficiency of atmospheric aerosols by raindrops

• Radioactive aerosols are removed from the atmosphere by precipitations in case of nuclear accident.
• Atmospheric aerosols and raindrops carry electric charges.
• Coulomb interactions need to be considered when investigating the removal of aerosols by raindrops.

Latest investigation completed at IRSN has revealed the substantial influence of flow morphology around the drops, in atmospheric washout of fine aerosol particles by precipitations, in complement to classical mechanisms. Moreover, several authors have claimed that rain drops during stormy rainfall carry millions of elementary electric charges which could increase by couple orders of magnitude the collection efficiency as a consequence of electrostatic forces. In non-thunderstorm clouds, model calculations indicate that the image charge effect resulting from aerosol charging can significantly affect their washout, even by uncharged raindrops.However, investigations on the influence of electric charges on aerosol washout (or collection efficiency) by simulated raindrops are very fragmented and contradictory.In this article, we report results of self-charged water drop generated by hypodermic needle over charge values comparable to those reported in the literature during stormy rainfall. We also controllably charged aerosol particles by corona discharge and evaluate how it affects their collection efficiency. Electric charges on drops and aerosols are precisely monitored by high resolution electrometers. Our preliminary results tend to accredit the impact of electric charges in collection efficiency.