With the implementation of COVID-19 restrictions and consequent improvement in air quality due to the nationwide lockdown, ozone (O 3 ) pollution was generally amplified in China. However, the O 3 levels throughout the Guangxi region of South China showed a clear downward trend during the lockdown. To better understand this unusual phenomenon, we investigated the characteristics of conventional pollutants, the influence of meteorological and anthropogenic factors quantified by a multiple linear regression (MLR) model, and the impact of local sources and long-range transport based on a continuous emission monitoring system (CEMS) and the HYSPLIT model. Results show that in Guangxi, the conventional pollutants generally declined during the COVID-19 lockdown period (January 24 to February 9, 2020) compared with their concentrations during 2016–2019, while O 3 gradually increased during the resumption (10 February to April 2020) and full operation periods (May and June 2020). Focusing on Beihai, a typical Guangxi region city, the correlations between the daily O 3 concentrations and six meteorological parameters (wind speed, visibility, temperature, humidity, precipitation, and atmospheric pressure) and their corresponding regression coefficients indicate that meteorological conditions were generally conducive to O 3 pollution mitigation during the lockdown. A 7.84 μg/m 3 drop in O 3 concentration was driven by meteorology, with other decreases (4.11 μg/m 3 ) explained by reduced anthropogenic emissions of O 3 precursors. Taken together, the lower NO 2 /SO 2 ratios (1.25–2.33) and consistencies between real-time monitored primary emissions and ambient concentrations suggest that, with the closure of small-scale industries, residual industrial emissions have become dominant contributors to local primary pollutants. Backward trajectory cluster analyses show that the slump of O 3 concentrations in Southern Guangxi could be partly attributed to clean air mass transfer (24–58%) from the South China Sea. Overall, the synergistic effects of the COVID-19 lockdown and meteorological factors intensified O 3 reduction in the Guangxi region of South China.

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In China, the corresponding control directives for volatile organic compounds (VOCs) have been based on primary emissions, rarely considering reactive speciation. To seek more effective VOCs control strategies, we investigated 107 VOC species in a typical coastal city (Beihai) of South China, from August to November 2018. Meanwhile, a high-resolution anthropogenic VOCs monthly emission inventory (EI) was established for 2018. For source apportionments (SAs) reliability, comparisons of source structures derived from positive matrix factorization (PMF) and EI were made mainly in terms of reaction losses, uncertainties and specific ratios. Finally, for the source–end control, a comprehensive reactivity control index (RCI) was established by combing SAs with reactive speciation profiles. Ambient measurements showed that the average concentration of VOCs was 26.38 ppbv, dominated by alkanes (36.7%) and oxygenated volatile organic compounds (OVOCs) (29.4%). VOC reactivity was estimated using ozone formation potential (52.35 ppbv) and propylene-equivalent concentration (4.22 ppbv). EI results displayed that the entire VOC, OFP, and propylene-equivalent emissions were 40.98 Gg, 67.98 Gg, and 105.93 Gg, respectively. Comparisons of source structures indicated that VOC SAs agreed within ±100% between two perspectives. Both PMF and EI results showed that petrochemical industry (24.0% and 33.0%), food processing and associated combustion (19.1% and 29.2%) were the significant contributors of anthropogenic VOCs, followed by other industrial processes (22.2% and 13.3%), transportation (18.9% and 12.0%), and solvent utilization (9.1% and10.5%). Aimed at VOCs abatement according to RCI: for terminal control, fifteen ambient highly reactive species (predominantly alkenes and alkanes) were targeted; for source control, the predominant anthropogenic sources (food industry, solvent usage, petrochemical industry and transportation) and their emitted highly reactive species were determined. Particularly, with low levels of ambient VOC and primary emissions, in this VOC and NOx double-controlled regime, crude disorganized emission from food industry contributed a high RCI.

This study provides the spatial, annual, and seasonal variations and the related human health risk assessment of PM 10 in the ambient air of Yangtze River Delta Region (YRDR). Daily average PM 10 concentrations of the 25 cities in this region in the previous 5 years (2005-2009) ranged from 52.8 to 112.1 lg/m 3 . PM 10 levels showed a decreasing trend for the major cities in the YRDR during this period. PM 10 mass was highest in winter (110.5 lg/m 3 ), followed by spring (95.9 lg/m 3 ) and summer (85.5 lg/m 3 ), with lowest concentration in autumn (78.2 lg/ m 3 ). For the potential health risk analysis, the residents were divided into four age categories, namely, infants, children (1 year), children (8-10 years), and adults. The analysis took into account age-specific breathing rates, body weights for different age categories. Risk analyses showed that the potential health risks due to respiratory disease were highest for all age categories in Xuzhou, followed by Yancheng, Hangzhou, and Nanjing, and the citizens in Zhoushan had the lowest health risks. The new information about the relationship between health risks and air pollution in YRDR may have implications for local environmental and social policies.

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