Journal Article

Co-benefits of reducing PM2.5 and improving visibility by COVID-19 lockdown in Wuhan

Cao, Wenxiang, Zhao, Tianliang, Yao, Liquan, Xu, Ke, Zhang, Zexuan, Hu, Yao, Zhu, Bo, Liu, Dantong, Chen, Nan, Cheng, Yi, Yan, Yingying, Zheng, Huang, Zhang, Ying, Qi, Shihua, Kong, Shaofei, Bai, Yongqing, Zheng, Mingming

2021

Overview

The less improvement of ambient visibility suspects the government’s efforts on alleviating PM 2.5 pollution. The COVID-19 lockdown reduced PM 2.5 and increased visibility in Wuhan. Compared to pre-lockdown period, the PM 2.5 concentration decreased by 39.0 μg m −3 , dominated by NH 4 NO 3 mass reduction (24.8 μg m −3 ) during lockdown period. The PM 2.5 threshold corresponding to visibility of 10 km (PTV 10 ) varied in 54–175 μg m −3 and an hourly PM 2.5 of 54 μg m −3 was recommended to prevent haze occurrence. The lockdown measures elevated PTV 10 by 9–58 μg m −3 as the decreases in PM 2.5 mass scattering efficiency and optical hygroscopicity. The visibility increased by 107%, resulted from NH 4 NO 3 extinction reduction. The NH 4 NO 3 mass reduction weakened its mutual promotion with aerosol water and increased PM 2.5 deliquescence humidity. Controlling TNO 3 (HNO 3  + NO 3 − ) was more effective to reduce PM 2.5 and improve visibility than NH x (NH 3  + NH 4 + ) unless the NH x reduction exceeded 11.7–17.5 μg m −3 .

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 704/172/169/824 / 704/172/169/896 / Ammonia / Ammonium nitrate / Atmospheric Sciences / Climate Change/Climate Change Impacts / Climatology / Coronaviruses / COVID-19 / Earth and Environmental Science / Earth Sciences / Haze / Hygroscopicity / Particulate matter / Reduction / Shelter in place / Visibility