Ice-Nucleating Particles Are Emitted by Raindrop Impact

Abstract

Ice-nucleating particles (INPs) play a key role in ice formation and cloud microphysics and thus significantly impact the water cycle and the climate. However, our understanding of atmospheric INPs, particularly their sources, emissions, and spatiotemporal variability, is incomplete. While the enhancement of atmospheric INP concentrations with rainfall has been previously shown, a mechanistic understanding of the process is lacking. Here, we link detailed precipitation observations with near-surface atmospheric INP concentrations at a semiarid grassland site in Colorado. Considering the during-precipitation air samples, INP concentrations positively correlate with cumulative rainfall kinetic energy and amount, suggesting that INP aerosolization is induced by raindrop and hailstone impact. By additionally analyzing the INP content of precipitation water, terrestrial source samples, and heat-treated samples, we demonstrate that local plants are the most plausible source of rain-induced INPs during a precipitation event. Should INPs aerosolized by precipitation rise to cloud height, they could influence cloud ice fraction and initiate precipitation resulting in an aerosol-cloud-precipitation feedback.