Observational Evidence of Lightning-Generated Ultrafine Aerosols

High temperature and pressure during lightning can quickly trigger multiple chemical reactions in the air, resulting in considerable impacts on aerosols, atmospheric chemistry, and air quality. Here, new particle formation (NPF) events motivated by lightning flashes were captured during an observation at Mt. Tai in summer 2017 for the first time. Numerous ultrafine particles were formed during the lightning events, leading to increases in nucleation and Aitken mode aerosols by 18.9 and 5.6 times, respectively. The formation rate (FR) and growth rate (GR) during lightning-generated NPF were 67.1 cm(-3)center dot s(-1) and 20.1 nm center dot h(-1), which were 61 and 1.7 times higher than the averaged daytime NPF. Moreover, chemical composition of aerosols was strongly influenced by lightning NOx. Nitrate aerosol (NO2- and NO3-) signals intensified significantly (by 11.9% and 12.4%, respectively) during the lightning-generated NPF, which contrasted with the sulfate aerosols measured in previous studies (non-lightning NPF). Meanwhile, lightning contributed noticeably to surface NO2 concentrations. Accompanying the uplifting airflows before rainfall, surface air pollutants (SO2, NH3, and NOx, etc.) can be transported above the top of the planet boundary layer, which plays an important role in NPF. The NPF in the hot lightning channels resulted from pollution NOx and lightning NOx, with the latter dominating. Finally, lightning-generated pollutants, including NOx and aerosols, were delivered down to the surface with descending airflows.

Automated summary

This study reveals the process of new particle formation in the atmosphere during lightning flashes, showing that lightning leads to the formation of ultrafine particles in the atmosphere and influences the chemical composition of atmospheric aerosols and air quality.