More Significant Impacts From New Particle Formation on Haze Formation During COVID-19 Lockdown

During the COVID-19 lockdown in 2020, large-scale industrial and transportation emissions were reduced, but high PM2.5 concentration still occurred. This study investigated the variation of particle number size distribution during the lockdown, and analyzed the characteristics of new particle formation (NPF) events and its potential impact on haze formation. Through measurement conducted in urban Beijing during the first 3 months of 2020, and comparison with year-over-year data, the decrease of primary Aitken-mode particles was observed. However, frequencies, formation rates and growth rates of NPF events remained stable between 2020 and 2019 in the same period. As a result, >25 nm particles produced by NPF events, would play a more important role in serving as the haze formation seeds compared to those produced by primary emissions. This finding emphasizes the significance on the understanding of NPF mechanisms when making pollution mitigation policy in the future.

Automated summary

During the COVID-19 lockdown in 2020, although large-scale industrial and transportation emissions were reduced, high PM2.5 concentration still occurred. The study found that NPF events played a significant role in haze formation despite the decrease in primary emissions. This highlights the importance of understanding NPF mechanisms in future pollution mitigation policies.