Increasing importance of ammonia emission abatement in PM2.5 pollution control

The coronavirus 2019(COVID-19)pandemic has severely affected human health and economic activity in countries around the world[1,2].To slow the spread of the COVID-19 outbreak,most countries have implemented a number of epidemic control interventions,including travel restrictions,business and industry closures,and requests for people to stay at home[2].In China,the lockdown started in Wuhan City on 23 January 2020 and vehicle movement was restricted there on 26 January 2020.These measures quickly expanded to the entire nation and lasted for＞3 weeks.Due to the abrupt and unprecedented restrictions on human activities,emissions of air pollutants were much reduced at local and national scales in China and other regions in the world during the lockdown[3-6].Recent studies found overall decreases in primary pollutants,but severe haze pollution still occurred[7,8].