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

作者：Liquan Yao, Shaofei Kong, Huang Zheng, Nan Chen, Bo Zhu, Ke Xu, Wenxiang Cao, Ying Zhang, Mingming Zheng, Yi Cheng, Yao Hu, Zexuan Zhang, Yingying Yan, Dantong Liu, Tianliang Zhao, Yongqing Bai, Shihua Qi · 发表于：npj Climate and Atmospheric Science · 年份：2021 · DOI：10.1038/s41612-021-00195-6 · 被引用次数：49 · 研究领域：COVID-19 impact on air quality、Air Quality and Health Impacts、Air Quality Monitoring and Forecasting

Abstract 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 .