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During the COVID-19 lockdown period (from January 23 to February 29, 2020), ambient PM2.5 concentrations in the Yangtze River Delta (YRD) region were observed to be much lower, while the maximum daily 8 h average (MDA8) O3 concentrations became much higher compared to those before the lockdown (from January 1 to 22, 2020). Here, we show that emission reduction is the major driving force for the PM2.5 change, contributing to a PM2.5 decrease by 37% to 55% in the four YRD major cities (i.e., Shanghai, Hangzhou, Nanjing, and Hefei), but the MDA8 O3 increase is driven by both emission reduction (29%–52%) and variation in meteorological conditions (17%– 49%). Among all pollutants, reduction in emissions mainly of primary PM contributes to a PM2.5 decrease by 28% to 46%, and NOx emission reduction contributes 7% to 10%. Although NOx emission reduction dominates the MDA8 O3 increase (38%–59%), volatile organic compounds (VOCs) emission reduction lead to a 5% to 9% MDA8 O3 decrease. Increased O3 promotes secondary aerosol formation and partially offsets the decrease of PM2.5 caused by the primary PM emission reductions. The results demonstrate that more coordinated air pollution control strategies are needed in YRD.

Epidemiological studies have shown that fine particulate matter (PM2.5) has adverse impacts on human health. However, limited studies have investigated the effects of short-term exposure to PM2.5 and its constituents on mortality in China. This study used the generalized linear model (GLM) to investigate the effects of PM2.5 and its constituents, including organic carbon (OC), element carbon (EC), ammonium (NH4+), nitrate (NO3−), sulfate (SO42−), on different causes of mortality in Shanghai from January 1, 2013 to December 31, 2015. The single-day lagged model and the moving average lagged model were used to examine the lagging effects of pollutants on mortality. At lag0 day, PM2.5 had a significant effect on all-cause mortality, and a 10 μg/m3 increase leads to 0.68% increase in all-cause mortality (RR 1.0068, 95%CI 1.0013–1.0123). Among the five constituents, EC had the greatest impact on all-cause mortality in Shanghai, with 10.48% increase of mortality (RR 1.1048, 95%CI 1.0266–1.1891) per 10 μg/m3 increase of concentrations, followed by OC (RR 1.0577, 95%CI 1.0277–1.0886), NH4+ (RR 1.0272, 95%CI 1.0028–1.0522) and SO42− (RR 1.0104, 95%CI 1.0003–1.0206). For respiratory diseases mortality, EC, OC, NO3− and NH4+ had significant impacts and caused an increase of mortality by 44.99% (RR 1.4499, 95%CI 1.1813–1.7794), 10.40% (RR 1.1040, 95%CI 1.0260–1.1880), 5.338% (RR 1.0533, 95%CI 1.0097–1.0989) and 7.34% (RR 1.0734, 95%CI 1.0015–1.1505) per 10 μg/m3 increase of concentrations, respectively. The cumulative effect of PM2.5 on mortality was significant in Shanghai. Except for SO42−, the RR value of the single-day lagged model was smaller than the moving average lagged model.

The North China Plain and the Yangtze River Delta are the two of the most heavily polluted regions in China. Observational studies revealed that ‘explosive’ PM2.5 mass concentration growths frequently occurred in the two regions. This study analyzed all the PM2.5 mass concentration growth processes from clean condition (i.e., 150 μg m−3) in Beijing (BJ) and Shanghai (SH), two representative cities of the two regions, using hourly monitored PM2.5 concentrations during 2013–2016. 173 and 76 growth processes were identified in BJ and SH, respectively. PM2.5 rising rates (PMRR) and dynamic growth durations were calculated to illustrate the characteristics of the growth processes. Hourly particulate chemical composition data and meteorological data in BJ and SH were further analyzed. The 4-year averaged PMRR of PM2.5 total mass were similarly of 7.11 ± 9.82 μg m−3 h−1 in BJ and 6.71 ± 6.89 μg m−3 h−1 in SH. A decreasing trend was found for the PM2.5 growth processes in two cities from 2013 to 2016, reflecting the effectiveness of emission controls implemented in the past years. The contributions of particulate components to the PM2.5 total mass growth were different in BJ and SH. Average PMRR value of PM1 organic aerosols (OA), SO42−, NO3−, and NH4+ in BJ was 1.90, 0.95, 0.82, and 0.53 μg m−3 h−1, respectively. Average PMRR of PM2.5 OA, SO42−, NO3−, and NH4+ in SH was 1.70, 1.18, 1.99 and 1.14 μg m−3 h−1, respectively. Based on the contributions of different components, the PM2.5 mass concentration growth processes in BJ and SH were proposed to be classified into ‘other components-dominant growth processes’, ‘all components-contributing growth processes’, ‘one or more explosive secondary components-dominant growth processes’, and ‘mixed-factor growth processes’. Potential source contribution function analysis and the meteorological condition analysis showed that source origins and prevailing wind for the two cities during different categories of growth processes had substantial difference. The important source areas included Hebei and Shandong for BJ, and Jiangsu and Anhui for SH. The dominant wind directions during growth processes were northeast, south and southwest in BJ, and were west to north in SH. The results suggested the contributing components, the prevailing wind conditions, and the formation processes were substantially different in the two cities, despite the similar PMRR of PM2.5 total mass during the growth processes between BJ and SH. Future research is needed to study the detailed formation mechanisms of the different PM2.5 mass concentration growth processes in the two cities.

The assessment of premature mortality associated with the dramatic changes in fine particulate matter (PM2.5) and ozone (O3) has important scientific significance and provides valuable information for future emission control strategies. Exposure data are particularly vital but may cause great uncertainty in health burden assessments. This study, for the first time, used six methods to generate the concentration data of PM2.5 and O3 in China between 2014 and 2018, and then quantified the changes in premature mortality due to PM2.5 and O3 using the Environmental Benefits Mapping and Analysis Program-Community Edition (BenMAP-CE) model. The results show that PM2.5-related premature mortality in China decreases by 263 (95% confidence interval (CI95): 142-159) to 308 (CI95: 213-241) thousands from 2014 to 2018 by using different concentration data, while O3-related premature mortality increases by 67 (CI95: 26-104) to 103 (CI95: 40-163) thousands. The estimated mean changes are up to 40% different for the PM2.5-related mortality, and up to 30% for the O3-related mortality if different exposure data are chosen. The most significant difference due to the exposure data is found in the areas with a population density of around 103 people/km2, mostly located in Central China, for both PM2.5 and O3. Our results demonstrate that the exposure data source significantly affects mortality estimations and should thus be carefully considered in health burden assessments.

PM2.5 and O3 controls are traditionally considered separately because PM2.5 is usually high in winter while O3 is generally high in summer. In this study, we explore the opportunity of controlling the two pollutants simultaneously through a better understanding of their intra-seasonal correlation and chemical-coupling behaviors under different meteorological conditions during the late summer and early fall (August–September) episodes in the San Joaquin Valley (SJV), California. A correlation analysis is first used to identify the temporal correlations between O3 and PM2.5 and their underlying physical and chemical drivers. Sensitivity analysis is then applied to determine the chemical coupling between PM2.5 and O3 and subsequent multipollutant control opportunities under two contrasting meteorological conditions using the Community Multi-Scale Air Quality (CMAQ) model. We find that O3 and PM2.5 are positively correlated on the daily timescale because both are sensitive to atmospheric stagnation. However, O3 and PM2.5 are negatively correlated on the hourly timescale determined by the negative correlation between hourly NO3− and O3, which is mainly due to the opposite effects of T and RH on the diurnal variations of NO3− and O3. Reducing NOx on average lead to O3 increase, but it can facilitate reducing O3 at higher O3 (>75 ppb) locations under the more stagnant conditions. NOx emission control could become beneficial for both O3 and PM2.5 when the NOx emissions in 2005 are further reduced by 15% under the more stagnant meteorological conditions and by 30% under the more ventilated meteorological conditions.

China has been suffering serious particulate matter (PM) pollution in recent decades. Local emission and regional transport both contribute to PM pollution. Determining the contributions of local emissions vs. regional transport to PM concentrations is crucial in making effective PM control policies. This paper reviews the recent research on the contributions of regional transport to PM pollution in four regions in China, i.e., the northern China, eastern China, southern China, and the western China, respectively. The major findings include (1) HYSPLIT is the most popular methods in studies in all regions and often is used in combination with the CA, PSCF, and CWT techniques to investigate the transport pathways and source origins; (2) during the relatively polluted period, transport contributes over 50% of the PM concentrations in Beijing, Shanghai, Hangzhou, Guangzhou, Hong Kong, and Chengdu. Regional transport is important for PM pollution in major cities of China; and (3) regional transport exhibits clear seasonal variations and long term trends. The findings have important implication for emission control programs in these regions.

As contamination is one of important factors to Panax notoginseng quality and safety. Saponin is one of important compounds with the medicinal values of P. notoginseng. The impact of soil As on production of saponin of P. notoginseng knew very little. This study was performed to determine content and heterogeneity of saponins from P. notoginseng and its mechanisms upon treatments with different concentration levels of As in soil. Plants of P. notoginseng were treated with arsenic [As (V)] at 0, 20, 80, 140, 20 and 260 mg/kg concentration levels which were supplied as sodium arsenate (Na3AsO4). These experimental plants were grown in shade condition in a greenhouse. Plants were harvested at vigorous vegetative growth and fruit ripening stages, separately. Effects of As treatments on saponin content, and heterogeneity of monomers in the mixtures of notoginesenosides and ginsenosides, enzymatic activity and gene expression level of squalene synthetase were determined for rhizome and main root tissues. Results show that：(1) Of all the As treatments from the lowest to the highest concentration levels, the As content in both rhizome and main roots from As-treated plants was within the standard level for superior products derived from P. notoginseng. The content of notoginsenosides from all tissues except the main roots at fruit ripening stage, was 5% higher than the standard level specified in the Chinese Pharmacopoeia; (2) The treatment of As at 20 mg/kg led to an 3.5% - 183.9% increases in total notoginesenosides content in rhizome and main roots, respectively. Treatments with the highest As concentration at 260 mg/kg resulted in a significant decline in total notoginsenosides content, and lower enzymatic activity and gene expression levels of squalene synthetase; (3) Under As treatment conditions, the ratio of Rb1/Rg1 decreased but the ratio of (Rb1 + Rg1)/R1 increased in both rhizomes and main roots. Conclusively, this study demonstrated that low As concentration (20 - 80 mg/kg) treatments resulted in higher notoginsenoside content in P. notoginseng. However, treatments with high As concentrations had an adverse effect. The repression in the synthesis of notoginsenoside and interruption of the conversion process from propanaxadiol into propanaxatriol are responsible for more heterogeneous monomer mixtures and low notoginsenoside content. For plants treated with the highest As concentration of 260 mg/kg, both gene expression and enzymatic activities of squalene synthetase were greatly repressed thus leading to a significantly low saponin content in rhizome and main root tissues.