Impact of primary emission variations on secondary inorganic aerosol formation: Prospective from COVID-19 lockdown in a typical northern China city. (15th April 2023)

• Record Type: Journal Article
• Authors: Duan, Xiaolin; Yan, Yulong; Xie, Kai; Niu, Yueyuan; Xu, Yang; Peng, Lin
• Is Part Of: Environmental pollution. Volume 323(2023)
• Publication Date: 2023-04-15
• Subjects: Secondary inorganic aerosol -- Reaction mechanisms -- Primary emissions -- Dominated pathways -- COVID-19; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2023.121355
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: Hourly observations in northern China city of Taiyuan were performed to compare secondary inorganic aerosol (SIA) reaction mechanisms, and emission effects on SIA during the pre-lock and COVID-19 lock days. Emission control implemented and meteorological conditions during lock days both caused beneficial impact on air quality. NO2 showed the highest decrease ratio of −49.5%, while the relative fraction of NO3 − in PM2.5 increased the most (2.7%). Source apportionment revealed the top three contributors to PM2.5 were secondary formation (SF), coal combustion (CC), and vehicle exhaust (VE) during both pre-lock and lock days. EC lock/pre were all lower than 1, suggesting the overall reduction of primary emissions during lock days, while the higher ratio of (SIA/EC) lock/pre (1.01–1.36) indicated the enhanced secondary formation in lock days. The ratio of SIA of pollution to clean days during lock periods considerably higher by 23.7% compared with that in pre-lock periods, which was indicated SIA secondary formation was more pronounced and contributed great to pollution days in lock periods though secondary formation existed in pre-lock and lock periods. Enhanced secondary formation of NO3 − and SO4 2− during lock days might be mainly due to the increased in aqueous and gas-phase reactions, respectively. Except for SF, high contribution of VE and CC were also important for high SIA concentration in pre-lock and lock days, respectively. The decreased contribution of VE weakens its contribution to SIA formation, indicating the effectiveness of VE emission control, as confirmed during the COVID-19 pandemic. This study highlights the aqueous and gas-phase reactions for nitrate and sulfate, respectively, which contributed to heavy pollution, as well as indicated the important role of VE on SIA formation, suggesting the urgent need to further strengthen controls on vehicle emissions. Graphical abstract: Image 1 Highlights: NO2 decreased mostly while NO3 − fraction in PM2.5 increased since lockdown. Enhanced secondary formation of SIA was found in heavy pollution days in lockdown. Aqueous and gas phase reaction dominated sulfate formation in pre-lockdown and lockdown. Aqueous phase reaction dominated nitrate formation in lockdown and pre-lockdown. Vital sources for SIA formation changed from vehicle exhaust to coal combustion.