Persistent ozone pollution episodes in North China exacerbated by regional transport

Ozone-Induced Lung Injury are Mediated Via PPAR-Mediated Ferroptosis in Mice

In recent years, the concentration of PM2.5 in China has decreased, while the concentration of ozone remains rising. Exposure to ozone contributes to respiratory illnesses; however, little is known about the underlying molecular mechanisms. The present study established an ozone-induced lung injury mice model to investigate potential molecular biomarkers and toxic mechanisms. Collected and analyzed the ozone pollution data in Xinxiang city from 2015 to 2022. At the same time, 24 male C57BL/6 mice were randomly assigned to control group and ozone exposure group. The ozone exposure concentration is 1 ppm, with 4 h of daily exposure for 33 consecutive days. HE staining was used to assess lung histological alterations and lung injury. High-throughput sequencing performed on the lung tissues of mice was used to analyze the differential expressed genes and signal transduction pathways. Xinxiang city is suffering from ozone pollution, especially in summer. HE staining showed that the ozone exposure could induce obvious inflammatory cell infiltration, alveolar wall thickening, or fracture. Transcriptome data revealed that there is a 145 differentially expressed genes between two groups and the genes enriched in PPAR signaling pathway, ferroptosis. The pivotal genes in the PPAR pathway including Adipoq, Lpl, Pck1, and Plin1 expression were significantly reduced. Additionally, the expression of Acsl6 and Scl7a11, which are close to PPAR pathway and ferroptosis has decreased. Ozone exposure could disrupt the lipid metabolism balance via downregulating lipid peroxidation-related genes through the PPAR signaling pathway, which further induced lung cell ferroptosis and aggravated lung injury in mice.

Determination of major drive of ozone formation and improvement of O3 prediction in typical North China Plain based on interpretable random forest model

O3 pollution in China has become prominent in recent years, and it has become one of the most challenging issues in air pollution control. We used data on atmospheric pollutants and meteorology from 2019 to 2021 to build an interpretable random forest (RF) model, applying this model to predict O3 concentration in 2022 in five cities in the Southwest North China Plain. The model was also used to identify and explain the influence of various factors on O3 formation. The correlation coefficient R2 between the predicted O3 concentration and observed O3 concentration was 0.82, the MAE was 15.15 μg/m3, and the RMSE was 20.29 μg/m3, indicating that the model can effectively predict O3 concentration in the studying area. The results of correlation analysis, feature importance, and the driving factor analysis from SHapley Additive exPlanations (SHAP) model indicated that temperature (T), NO2, and relative humidity (RH) are the top three features affecting O3 prediction, while the weights of wind speed and wind direction were relatively low. Thus, O3 in the southwestern North China Plain may mainly come from the formation of local photochemical activities. The dominant factors behind O3 also varied in different seasons. In spring and autumn, O3 pollution is more likely to occur under high NO2 concentration and high-temperature conditions, while in summer, it is more likely to occur under high-temperature and precipitation-free weather. In winter, NO2 is the dominant factor in O3 formation. Finally, the interpretable RF model is used to predict future O3 concentration based on features provided by Community Multiscale Air Quality (CMAQ) and Weather Research & Forecast (WRF) model, and the simulation performance of CMAQ on O3 concentration is enhanced to a certain extent, improving the prediction of future O3 pollution situations and guiding pollution control.

Spatiotemporal evolution and key driver analysis of ozone pollution from the perspectives of spatial spillover and path-dependence effects in China

In recent years, ozone (O3) has emerged as the primary air pollutant in China, superseding PM2.5. Previous studies have concentrated on the spatiotemporal variation of ozone pollution, the analysis of its sources and drivers, as well as its environmental impacts and health benefits. Since ozone pollution can be dynamically transferred through industrial activities and meteorological factors, it is crucial to scientifically identify the spatial spillover and path-dependent effects of ozone pollution in China. However, existing studies have not yet addressed this issue. Therefore, we investigate the spatiotemporal evolution and the spatial spillover of ozone pollution by means of the exploratory spatial data analysis (ESDA) using panel data of 30 Chinese provinces from 2013 to 2020 in this study. The dynamic spatial Durbin model (SDM) was employed to reveal the key drivers of ozone pollution from the perspectives of spatial spillover and path-dependence effects. The direct and spillover effects of each driver on ozone pollution are systematically analyzed. The results show that from 2013 to 2020 ozone concentrations followed a fluctuating upward trend at national and provincial scales. Ozone pollution presented significant spatial spillover and path dependence effects. The direct effects indicated that economic growth, technological level, industrial structure, energy structure, ventilation coefficient, relative humidity and precipitation were the key drivers of local ozone pollution. The spillover effects indicated that population density, technology level, industrial structure, environmental regulations, ventilation coefficient, sunshine hours and relative humidity had significant spatial spillover effects on ozone pollution of surrounding regions. These findings will contribute to the understanding of the spatial spillover and path-dependent effects of O3 pollution, and provide scientific guidance for regional synergy and long-term ozone control policies in China.

Research on regional ozone prevention and control strategies in eastern China based on pollutant transport network and FNR

O3 pollution in China has worsened sharply in recent years, and O3 formation sensitivity (OFS) in many regions have gradually changed, with eastern China as the most typical region. This study constructed the transport networks of O3 and NO2 in different seasons from 2017 to 2020. The transport trends and the clustering formation patterns were summarized by analyzing the topological characteristics of the transport networks, and the patterns of OFS changes were diagnosed by analyzing the satellite remote sensing data. Based on that, the main clusters that each province or city belongs to in different pollutant transport networks were summarized and proposals for the inter-regional joint prevention and control were put forward. As the results showed, O3 transport activity was most active in spring and summer and least active in winter, while NO2 transport activity was most active in autumn and winter and least active in summer. OFS in summer mainly consisted of transitional regimes and NOx-limited regimes, while that in other seasons was mainly VOC-limited regimes. Notably, there was a significant upward trend in the proportion of transitional regimes and NOx-limited regimes in spring, autumn, and winter. For regions showing NOx-limited regime, areas with higher out-weighted degrees in the NO2 transport network should focus on controlling local NOx emissions, such as central regions in summer. For regions showing VOC-limited regime, areas with higher out-weighted degrees in the O3 transport network should focus on controlling local VOCs emissions, such as central and south-central regions in summer. For regions that belong to the same cluster and present the same OFS in each specific season, regional cooperative emission reduction strategies should be established to block important transmission paths and weaken regional pollution consistency.

Spatial and temporal variations of surface background ozone in China analyzed with the grid-stretching capability of GEOS-Chem High Performance

Surface background ozone, defined as the ozone in the absence of domestic anthropogenic emissions, is important for developing emission reduction strategies. Here we apply the recently developed GEOS-Chem High Performance (GCHP) global atmospheric chemistry model with ∼0.5° stretched resolution over China to understand the sources of Chinese background ozone (CNB) in the metric of daily maximum 8 h average (MDA8) and to identify the drivers of its interannual variability (IAV) from 2015 to 2019. The GCHP ozone simulations over China are evaluated with an ensemble of surface and aircraft measurements. The five-year national-mean CNB ozone is estimated as 37.9 ppbv, with a spatially west-to-southeast downward gradient (55 to 25 ppbv) and a summer peak (42.5 ppbv). High background levels in western China are due to abundant transport from the free troposphere and adjacent foreign regions, while in eastern China, domestic formation from surface natural precursors is also important. We find greater importance of soil nitric oxides (NOx) than biogenic volatile organic compound emissions to CNB ozone in summer (6.4 vs. 3.9 ppbv), as ozone formation becomes increasingly NOx-sensitive when suppressing anthropogenic emissions. The percentage of daily CNB ozone to total surface ozone generally decreases with increasing daily total ozone, indicating an increased contribution of domestic anthropogenic emissions on polluted days. CNB ozone shows the largest IAV in summer, with standard deviations (seasonal means) of ∼5 ppbv over Qinghai-Tibet Plateau (QTP) and >3.5 ppbv in eastern China. CNB values in QTP are strongly correlated with horizontal circulation anomalies in the middle troposphere, while soil NOx emissions largely drive the IAV in the east. El Nino can inhibit CNB ozone formation in Southeast China by increased precipitation and lower temperature locally in spring, but enhance CNB in Southwest China through increased biomass burning emissions in Southeast Asia.

Impact of spatial scales of control measures on the effectiveness of ozone pollution mitigation in eastern China

Ozone (O3) pollution is becoming the primary air pollution issue with the large decrease in fine particulate concentrations in eastern China. The development of widely recognized policies for controlling O3 pollution episodes is urgent. This study aims to provide actionable and comprehensive suggestions for O3 control policy development, with an emphasis on the precursor emission reductions. Here, we compared the impacts of different spatial scale reductions on a widespread O3 pollution episode in eastern China by a state-of-the-art regional air quality model. We find that region-scale joint control (in >30 cities) is much more effective than city-scale sporadic reduction in reducing O3 concentration. Sporadic controls only reduce the maximum daily 8-h average (MDA8) O3 by ∼1 μg/m3 in the controlled city, whereas regional controls lead to a MDA8 O3 decrease of ∼8 μg/m3 in the controlled region. In addition, the emission reduction effectiveness increased by 2.6 times from <5 cities to >30 cities. Continuous reductions have a cumulative effect on the decrease of MDA8 O3, showing the strongest effects within 24 h and diminishing after 48 h, which underscores the importance of reducing emissions 24 h prior to an episode. Moreover, the effect of control measures on MDA8 O3 varies spatially depending on the ratio of volatile organic compounds (VOCs) to nitrogen oxides (NOx) (VOCs/NOx). Both the reductions of VOC and NOx emissions have a positive effect on the decrease of MDA8 O3 in summer, but the effects of VOC reductions are 1.2 to 1.7 times higher than those of NOx reductions. The residential sector, due to its high VOCs/NOx emission ratio, exhibits the highest efficiency in the reduction of O3 concentrations. Our results highlight the importance of regional joint control and synergistic reduction of VOCs and NOx in eastern China.

Integrated analysis of the transport process and source attribution of an extreme ozone pollution event in Hefei at different vertical heights: A case of study

The Yangtze River Delta (YRD) region frequently experiences ozone pollution events during the summer and autumn seasons. High-concentration events are typically related to synoptic weather patterns, which impact the transport and photochemical production of ozone at multiple scales, ranging from the local to regional scale. To better understand the regional ozone pollution problem, studies on ozone source attribution are needed, especially regarding the contributions of sources at different vertical heights based on tagging the region or time periods. Between September 3 and 8, 2020, an episode of ozone concentration anomaly high was observed in Hefei through ground-based stations and ozone Lidar. The mechanism behind this event was uncovered through synoptic weather pattern analysis and using the Weather Research and Forecasting Chemistry model (WRF-Chem). Because an approaching typhoon caused variable wind direction, the O3-rich air masses (ORMs) arising from the YRD region were transported to Hefei via the nocturnal residual layer and descended to the ground through horizontal advection and vertical mixing processes the next day. Based on geographic source tagging, the anthropogenic NOx emissions (ANEs) from local and regional sources were the main contributors to the heavy ozone pollution over Hefei on September 6. Furthermore, the intra-regional transported ozone from southern Jiangsu (SJS), southern Anhui (SAH), and Zhejiang (ZJ) in the YRD was the main driving factor of the surface and upper atmosphere ozone pollution. Based on time period tagging, The ozone generated due to ANEs from September 3 to 5 significantly contributed to this episode. It is important to pay attention to the impact of ANEs on September 5 on the surface peak ozone concentration the following day (i.e., September 6). Our findings provide significant insights into the regional ozone transport mechanism in the YRD and optimization of measures to prevent and control heavy ozone pollution on spatiotemporal scales.

Spatial clustering and spillover pathways analysis of O3, NO2, and CO in eastern China during 2017-2021

The eastern China presented the most serious O3 pollution and increasingly prominent regional characteristics. To understand the transport characteristics of O3 and its precursors and identify their potential relationships are of great guiding significance for interregional joint prevention and control. In this study, the annual and seasonal transport networks of O3 and its precursors (NO2 and CO) during 2017-2021 were constructed by applying the complex network method to air quality observations. And the key spatial clusters, the spillover paths and the potential links among pollutants were comprehensively analyzed based on the topological characteristic analysis of the established air pollutant transport networks. As the results showed, O3 pollution in the eastern China was affected by active regional transports of O3 and its precursors. Regional transports of O3, NO2, and CO were more prominent in autumn and showed high synchronization. The regional transport of precursors, especially NOx, was an important cause of regional O3 pollution. Air pollutant transport characteristics varied with seasons and regions, which demonstrating the importance of regulating seasonal and regional differentiated joint prevention and control strategies, especially for NOx. The results of this study can provide science-based guidance for the regional cooperative control of O3 pollution in the eastern China, and the application of complex networks can also provide a new methodological perspective for the study of air pollution transmission.

A regional cooperative reduction game model for air pollution control in North China

Due to variations in economic scale, economic structure, and technological advancement across different Chinese provinces and cities, the cost of air pollution reduction differs significantly. Therefore, the total reduction cost can be decreased by capitalizing on these regional discrepancies in reduction cost to carry out cooperative emission reduction. In this paper, taking NOx reduction in North China as an example, a regional cooperative reduction game (CRG) model was constructed to minimize the total cost of emission reduction while achieving future emission reduction targets. The fair allocation of benefits from cooperation plays a crucial role in motivating regions to participate into the cooperation. A comprehensive mechanism of benefits allocation was proposed to achieve fair transferred compensation. The mechanism combines the consumption responsibility principle based on input-output theory and the Shapley value method based on game theory. Compared to the cost before the optimized collaboration, the CRG model will save 20.36% and 13.71% of the total reduction cost in North China, respectively, under the target of 17.68% NOx reduction by 2025 and 66.44% NOx reduction by 2035 relative to 2020. This method can be employed in other regions to achieve targets for air pollution reduction at minimum cost, and to motivate inter-regional cooperation with this practical and fair way of transferred compensation.

O3 transport characteristics in eastern China in 2017 and 2021 based on complex networks and WRF-CMAQ-ISAM

Increasingly prominent pollution levels and strong regional characteristics of O₃, especially in economically developed eastern China, called for a regional cooperation strategy based on transport quantification. This study adopted the complex networks to construct the O₃ Transport Network (OTN) to explore characteristics in eastern China in the summer of 2017 and 2021, whose results were afterward verified with spatial source apportionment results simulated with WRF-CMAQ-ISAM. As OTN suggested, O₃ transport showed stronger and faster characteristics in eastern China in 2021 than in 2017, judging from changes in the network density, number of connections, transport ranges, and transport paths. Among all cluster communities, inland Shandong was the most important O₃ transport hub, the Central Community was the largest community, and the Southern Community showed the closest inter-city transport relationships. In- and out-weighted degrees in OTN showed relatively superior consistency with the transport matrix obtained with WRF-CMAQ-ISAM, and can be explained by wind fields. Generally, O₃ pollution in the whole eastern China showed more frequent intra-regional transport and more strengthened inter-city correlations in 2021 than in 2017, meanwhile, northerly and southerly cities exhibited strengthening and weakening trends in O₃ transport, respectively. Despite the completely different principles of complex networks and air quality models, their results were mutually verifiable. This study presented a comprehensive understanding of O₃ transport in eastern China for further formulation of regional collaborative strategies and provided the methodological verification for applying complex networks in the atmospheric environment field.

Drivers of Increasing Ozone during the Two Phases of Clean Air Actions in China 2013-2020

In response to the severe air pollution issue, the Chinese government implemented two phases (Phase I, 2013-2017; Phase II, 2018-2020) of clean air actions since 2013, resulting in a significant decline in fine particles (PM_2.5) during 2013-2020, while the warm-season (April-September) mean maximum daily 8 h average ozone (MDA8 O₃) increased by 2.6 μg m^-3 yr^-1 in China during the same period. Here, we derived the drivers behind the rising O₃ concentrations during the two phases of clean air actions by using a bottom-up emission inventory, a regional chemical transport model, and a multiple linear regression model. We found that both meteorological variations (3.6 μg m^-3) and anthropogenic emissions (6.7 μg m^-3) contributed to the growth of MDA8 O₃ from 2013 to 2020, with the changes in anthropogenic emissions playing a more important role. The anthropogenic contributions to the O₃ rise during 2017-2020 (1.2 μg m^-3) were much lower than that in 2013-2017 (5.2 μg m^-3). The lack of volatile organic compound (VOC) control and the decline in nitrogen oxides (NO_x) emissions were responsible for the O₃ increase in 2013-2017 due to VOC-limited regimes in most urban areas, while the synergistic control of VOC and NO_x in Phase II initially worked to mitigate O₃ pollution during 2018-2020, although its effectiveness was offset by the penalty of PM_2.5 decline. Future mitigation efforts should pay more attention to the simultaneous control of VOC and NO_x to improve O₃ air quality.

Impacts of synoptic circulation on surface ozone pollution in a coastal eco-city in Southeastern China during 2014-2019

The coastal eco-city of Fuzhou in Southeastern China has experienced severe ozone (O₃) episodes at times in recent years. In this study, three typical synoptic circulations types (CTs) that influenced more than 80% of O₃ polluted days in Fuzhou during 2014-2019 were identified using a subjective approach. The characteristics of meteorological conditions linked to photochemical formation and transport of O₃ under the three CTs were summarized. Comprehensive Air Quality Model with extensions was applied to simulate O₃ episodes and to quantify O₃ sources from different regions in Fuzhou. When Fuzhou was located to the west of a high-pressure system (classified as "East-ridge"), more warm southwesterly currents flowed to Fuzhou, and the effects of cross-regional transport from Guangdong province and high local production promoted the occurrence of O₃ episodes. Under a uniform pressure field with a low-pressure system occurring to the east of Fuzhou (defined as "East-low"), stagnant weather conditions caused the strongest local production of O₃ in the atmospheric boundary layer. Controlled by high-pressure systems over the mainland (categorized as "Inland-high"), northerly airflows enhanced the contribution of cross-regional transport to O₃ in Fuzhou. The abnormal increases of the "East-ridge" and "Inland-high" were closely related to O₃ pollution in Fuzhou in April and May 2018, resulting in the annual maximum number of O₃ polluted days during recent years. Furthermore, the rising number of autumn O₃ episodes in 2017-2019 was mainly related to the "Inland-high", indicating the aggravation of cross-regional transport and highlighting the necessity of enhanced regional collaboration and efforts in combating O₃ pollution.

Divergent summertime surface O3 pollution formation mechanisms in two typical Chinese cities in the Beijing-Tianjin-Hebei region and Fenwei Plain

Recently, severe summertime ozone (O₃) pollution has swept across most areas of China, especially the Beijing-Tianjin-Hebei (BTH) region and Fenwei Plain. By focusing on Beijing and Yuncheng, which are two typical cities in the BTH region and the Fenwei Plain, we intended to reveal the neglected fact that they had disparate emission features and atmospheric movements but suffered from similar high-O₃ pollution levels. Field observations indicated that Yuncheng had lower volatile organic compound (VOC) and NO_x concentrations but higher background O₃ levels. The model simulation verified that both photochemical reactions and net O₃ generation were stronger in Beijing. Ultimately, faster net O₃ generation rates (8.4 ppbv/h) plus lower background O₃ values in Beijing and lower net O₃ generation rates (6.2 ppbv/h) plus higher background O₃ values in Yuncheng caused both regions to reach similar O₃ peak values in July 2020. However, different O₃ control measures were appropriate for the two cities according to the different simulated O₃-VOCs-NO_x responses. Additionally, as surface O₃ levels are greatly affected by the ongoing O₃ production/depletion process that occurs in three dimensions, exploring the effects of spatially distributed O₃ on surface O₃ should be high on the agenda in the future.

An investigation on the role of electric vehicles in alleviating environmental pollution: evidence from five leading economies

The relationship between battery electric vehicles (BEV) and carbon dioxide emission (CO₂) has significant environmental outcomes. Notwithstanding, battery electric vehicles have not been extensively explored through econometric approach. For countries to meet their net zero targets, it is crucial to consider the role of battery electric vehicles, renewable energy consumption, and CO₂. As a result, it is critical to scrutinize a variety of variables that contribute to a sustainable future. This study therefore examines the dynamic correlation between BEV, gross domestic product (GDP), urbanization (URB), renewable energy consumption (REC), population (POP), and CO₂ in five leading countries (the United States of America (USA), China, France, Germany, and Norway) using panel data from 2010 to 2020. The study adopted the Westerlund cointegration method to ascertain the long-term nexus among the series. The cross-sectionally augmented autoregressive distributed lag CS-ARDL technique is adopted to evaluate the variables long-run elasticity. The study applied the common correlated effect mean group (CCEMG) and augmented mean group (AMG) approach to ascertain the robustness of the long-run relationships among the variables. Dumitrescu and Hurlin's panel causality analysis determines the extent of the significant causality linkage. The results demonstrate that increased economic growth, urbanization, and population growth accelerate carbon emissions and environmental depletion. However, BEVs were found to be more energy efficient and the adoption of renewable energy through the manufacturing and battery production process would reduce CO₂ emission especially in China and the USA. Finally, the research proposed several policy implications for policy and decision-makers in the five leading countries for combating climate change and increasing productivity in the electric vehicle market and renewable energy consumption.

Understanding and revealing the intrinsic impacts of the COVID-19 lockdown on air quality and public health in North China using machine learning

To avoid the spread of COVID-19, China implemented strict prevention and control measures, resulting in dramatic variations in urban and regional air quality. With the complex effect from long-term emission mitigation and meteorology variation, an accurate evaluation of the net effect from lockdown on air quality changes has not been fully quantified. Here, we combined machine learning algorithm and Theil-Sen regression technique to eliminate meteorological and long-term trends effects on air pollutant concentrations and precisely detect concentrations changes those ascribed to lockdown measures in North China. Our results showed that, compared to the same period in 2015-2019, the adverse meteorology during the lockdown period (January 25th to March 15th) in early 2020 increased PM_2.5 concentration in North China by 9.8 %, while the reduction of anthropogenic emissions led to a 32.2 % drop. Stagnant meteorological conditions have a more significant impact on the ground-level air quality in the Beijing-Tianjin-Hebei Region than that in Shanxi and Shandong provinces. After further striping out the effect of long-term emission reduction trend, the lockdown-derived NO₂, PM_2.5, and O₃ shown variety change trend, and at -30.8 %, -27.6 %, and +10.0 %, respectively. Air pollutant changes during the lockdown could be overestimated up to 2-fold without accounting for the influences of meteorology and long-term trends. Further, with pollution reduction during the lockdown period, it would avoid 15,807 premature deaths in 40 cities. If with no deteriorate meteorological condition, the total avoided premature should increase by 1146.

Ozone-3,6-dihydroxynaphtha-2,7-disulphonate chemiluminescence system is used for online ozone detection

The chemiluminescence (CL) reaction between ozone and 3,6-dihydroxynaphtha-2,7-disulphonate (DNDS) was found under alkaline conditions. Therefore, a novel CL system for ozone detection was established. The CL signal of the CL system is weak, and the CL signal is enhanced by adding nonionic surfactants. It was found that adding 16.4 g/l Triton X-100 can enhance the CL signal. The CL reagent activated by ultraviolet (UV) light produced a CL signal was nearly 10 times stronger than the CL reagent not activated by UV light; the CL signal was enhanced by adding 8 g/l NaHCO₃ to the CL reagent irradiated by UV light. Through the optimization of these test conditions, a high-selectivity, high-sensitivity online detection method for ozone CL was established. The linear range was 0.5-150 ppbv, and the limit of detection (LOD) was 0.092 ppbv (S/N = 3).

Assessing the contribution of open crop straw burning to ground-level ozone and associated health impacts in China and the effectiveness of straw burning bans

In recent years, ozone pollution in China has been shown to increase in frequency and persistence despite the concentrations of fine particulate matter (PM_2.5) decreasing steadily. Open crop straw burning (OCSB) activities are extensive in China and emit large amounts of trace gases during a short period that could lead to elevated ozone concentrations. This study addresses the impacts of OCSB emissions on ground-level ozone concentration and the associated health impact in China. Total VOCs and NOx emissions from OCSB in 2018 were 798.8 Gg and 80.6 Gg, respectively, with high emissions in Northeast China (31.7%) and North China (23.7%). Based on simulations conducted for 2018, OCSB emissions are estimated to contribute up to 0.95 µg/m³ increase in annual averaged maximum daily 8-hour (MDA8) ozone and up to 1.35 µg/m³ for the ozone season average. The significant impact of OCSB emissions on ozone is mainly characterized by localized and episodic (e.g., daily) changes in ozone concentration, up to 20 µg/m³ in North China and Yangtze River Delta region and even more in Northeast China during the burning season. With the implementation of straw burning bans, VOCs and NOx emissions from OCSB dropped substantially by 46.9%, particularly over YRD (76%) and North China (60%). Consequently, reduced OCSB emissions result in an overall decrease in annual averaged MDA8 ozone, and reductions in monthly MDA8 ozone could be over 10 µg/m³ in North China. The number of avoided premature death due to reduced OCSB emissions (considering both PM_2.5 and ozone) is estimated to be 6120 (95% Confidence Interval: 5320-6800), with most health benefits gained over east and central China. Our results illustrate the effectiveness of straw burning bans in reducing ozone concentrations at annual and national scales and the substantial ozone impacts from OCSB events at localized and episodic scales.

The relationship between the intensified heat waves and deteriorated summertime ozone pollution in the Beijing-Tianjin-Hebei region, China, during 2013-2017

Summertime ozone (O₃) pollution has frequently occurred in the Beijing-Tianjin-Hebei (BTH) region, China, since 2013, resulting in detrimental impacts on human health and ecosystems. The contribution of weather shifts to O₃ concentration variability owing to climate change remains elusive. By combining regional air chemistry model simulations with near-surface observations, we found that anthropogenic emission changes contributed to approximately 23% of the increase in maximum daily 8-h average O₃ concentrations in the BTH region in June-July-August (JJA) 2017 (compared with that in 2013). With respect to the weather shift influence, the frequencies, durations, and magnitudes of O₃ exceedance were consistent with those of the heat wave events in the BTH region during JJA in 2013-2017. Intensified heat waves are a significant driver for worsening O₃ pollution. In particular, the prolonged duration of heat waves creates consecutive adverse weather conditions that cause O₃ accumulation and severe O₃ pollution. Our results suggest that the variability in extreme summer heat is closely related to the occurrence of high O₃ concentrations, which is a significant driver of deteriorating O₃ pollution.

Summer ozone pollution in China affected by the intensity of Asian monsoon systems

Ozone in the troposphere is harmful to human health and ecosystems. It has become the most severe air pollutant in China. Here, based on global atmospheric chemistry model simulations during 1981-2019 and nation-wide surface observations, the impacts of interannual variations in Asian summer monsoon (ASM), including East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM), on surface O₃ concentrations during June-July-August (JJA) in China are investigated. EASM intensity has a significant positive correlation with the surface O₃ concentration in south-central China (97.5°-117.5°E, 20°-35°N) with a correlation coefficient of 0.6. Relative to the weak EASM years, O₃ concentrations in strong EASM years increased by up to 5 ppb (10 % relative to the average) due to the weakened transboundary transport of O₃ resulting from the decrease in prevailing southwesterlies. SASM can be divided into two components. The one near East Asia has a similar relation with O₃ in southern China (100°-117.5°E, 22°-32°N) as that of EASM. The other component of SASM is negatively correlated with surface O₃ concentration in eastern China (110°-117.5°E, 22°-34°N) and the maximum difference in O₃ concentrations exceeded 5 ppb (10 %) between the strong and weak monsoon years, which can be explained by the O₃ divergence caused by the anomalous southerlies blowing pollutants away from the northern boundary of eastern China. This study shows that the ASM has an important impact on the O₃ concentrations in China, primarily through changing transboundary transport related to the variability of large-scale circulations, which has great implications for air pollution prevention and mitigation in China. Future projections of ASM suggests that the sustainable and medium development scenarios are the perfect pathways that can help to mitigate O₃ pollution, while high social vulnerability and radiative forcing scenarios could enhance future O₃ pollution in China.

Spatiotemporal Variation in Ground Level Ozone and Its Driving Factors: A Comparative Study of Coastal and Inland Cities in Eastern China

Variations in marine and terrestrial geographical environments can cause considerable differences in meteorological conditions, economic features, and population density (PD) levels between coastal and inland cities, which in turn can affect the urban air quality. In this study, a five-year (2016-2020) dataset encompassing air monitoring (from the China National Environmental Monitoring Centre), socioeconomic statistical (from the Shandong Province Bureau of Statistics) and meteorological data (from the U.S. National Centers for Environmental Information, National Oceanic and Atmospheric Administration) was employed to investigate the spatiotemporal distribution characteristics and underlying drivers of urban ozone (O₃) in Shandong Province, a region with both land and sea environments in eastern China. The main research methods included the multiscale geographically weighted regression (MGWR) model and wavelet analysis. From 2016 to 2019, the O₃ concentration increased year by year in most cities, but in 2020, the O₃ concentration in all cities decreased. O₃ concentration exhibited obvious regional differences, with higher levels in inland areas and lower levels in eastern coastal areas. The MGWR analysis results indicated the relationship between PD, urbanization rate (UR), and O₃ was greater in coastal cities than that in the inland cities. Furthermore, the wavelet coherence (WTC) analysis results indicated that the daily maximum temperature was the most important factor influencing the O₃ concentration. Compared with NO, NO₂, and NO_x (NO_x ≡ NO + NO₂), the ratio of NO₂/NO was more coherent with O₃. In addition, the temperature, the wind speed, nitrogen oxides, and fine particulate matter (PM_2.5) exerted a greater impact on O₃ in coastal cities than that in inland cities. In summary, the effects of the various abovementioned factors on O₃ differed between coastal cities and inland cities. The present study could provide a scientific basis for targeted O₃ pollution control in coastal and inland cities.

Spatiotemporal variation of ozone pollution and health effects in China

With the rapid urbanization and industrialization in China, ozone pollution has become increasingly serious and poses a greater threat to human health. In this study, the spatiotemporal distribution of ozone pollution in China's cities and urban agglomerations from 2015 to 2019 was analyzed. The health effects and health economic costs of ozone pollution in China were estimated by applying the environmental Benefits Mapping and Analysis Program-Community Edition (BenMAP-CE) model. The results are as follows: (1) ozone pollution was more serious in Chinese urban agglomerations from 2015 to 2019; (2) the hot spots of ozone concentration mainly distributed in the North China Plain, expanding from north to south; the cold spots decreased year by year and were located in the northeast, northwest, and southwest of China, shifting from northwest to southwest; (3) the seasonal average of ozone concentration in China was the highest in summer, followed by spring and autumn, and the lowest in winter; (4) the number of all-cause premature deaths of ozone pollution in China increased slowly from 2015 to 2019, and the average of urban agglomerations was significantly higher than cities, with similar spatial distribution characteristics as ozone concentration; (5) the health economic costs of ozone pollution from 2015 to 2019 slowly expanded to surrounding cities with Beijing, Shanghai, Xi'an, and Chongqing as the centers of high values, while the low value areas decreased year by year and were mainly concentrated in southwest and northeast China. The health economic costs of ozone pollution at urban agglomerations scale were higher in the eastern coastal regions and lower in the northwest inland regions. Thus, this study presents policy recommendations to provide decision-making reference for realizing the inter-regional prevention and control of ozone pollution.

Curcumin Modifies the Activity of Plasmatic Antioxidant Enzymes and the Hippocampal Oxidative Profile in Rats upon Acute and Chronic Exposure to Ozone

Ozone (O₃) is an oxidating tropospheric pollutant. When O₃ interacts with biological substrates, reactive oxygen and nitrogen species (RONS) are formed. Severe oxidative damage exhausts the endogenous antioxidant system, which leads to the decreased activity of antioxidant enzymes such as catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD). Curcumin (CUR) is a natural polyphenol with well-documented antioxidant and anti-inflammatory properties. The aim of this work is to evaluate the effects of curcumin on CAT, GPx, and SOD activity and the inhibition of oxidative damage after the acute and chronic exposure to O₃. Fifty male Wistar rats were divided into five experimental groups: the intact control, CUR-fed control, exposed-to-O₃ control, CUR-fed (preventive), and CUR-fed (therapeutic) groups. These two last groups received a CUR-supplemented diet while exposed to O₃. These experiments were performed during acute- and chronic-exposure phases. In the preventive and therapeutic groups, the activity of plasma CAT, GPx, and SOD was increased during both exposure phases, with slight differences; concomitantly, lipid peroxidation and protein carbonylation were inhibited. For this reason, we propose that CUR could be used to enhance the activity of the antioxidant system and to diminish the oxidative damage caused by exposure to O₃.

Atmospheric transport drives regional interactions of ozone pollution in China

In recent years, ozone pollution becomes a serious environmental issue in China. A good understanding of source-receptor relationships of ozone transport from aboard and inside China is beneficial to mitigating ozone pollution there. To date, these issues have not been comprehensively assessed, especially for highly polluted regions in the central and eastern China (CEC), including the North China Plain (NCP), Twain-Hu region (THR), Yangtze River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SCB). Here, based on simulations over 2013-2020 from a well-validated chemical transport model, GEOS-Chem, we show that foreign ozone accounts for a large portion of surface ozone over CEC, ranging from 25.0% in THR to 39.4% in NCP. Focusing on transport of domestic ozone between the five regions in CEC, we find that atmospheric transport can largely modulate regional interactions of ozone pollution in China. At the surface, THR receives the largest amount of ozone from the other four regions (54.2% of domestic ozone in the receptor region, the same in below), followed by PRD (32.3%), SCB (26.7%), YRD (21.1%), and NCP (18.0%). Meanwhile, YRD exports largest amount of ozone to the other regions, ranging from 8.9% in SCB to 28.4% in THR. Although SCB is relatively isolated and thus impacts NCP, YRD, and PRD weakly (< 2.2%), export of SCB ozone to THR reaches 9.3%. The regional ozone transport over CEC, occurring mostly in the lower troposphere, is mainly modulated by the East Asian monsoon circulations, proximity between source and receptor regions, seasonal changes of ozone production, and topography.

Vertical characteristics of NO2 and HCHO, and the ozone formation regimes in Hefei, China

The research on the mechanism of combined air pollution in the Yangtze-Huaihe region, which is characterized by unique meteorological and geographical conditions and pollution emission characteristics, is still insufficient. We performed an experiment on key pollutants and an ozone formation study in Hefei, which is a pivotal city in the Yangtze-Huaihe region, from September 1 to 20, 2020. The aerosols retrieved via two-dimensional Multi-axis Differential Optical Absorption Spectroscopy (2D-MAX-DOAS) with a Boltzmann-shaped a priori profile had the best agreement with the results of Light Detection and Ranging (LIDAR) and sun-photometer measurements among the three typical a priori profiles (Gaussian, Boltzmann, and exponential shapes). The correlation coefficients of the near-surface gas concentrations retrieved using both 2D-MAX-DOAS and in situ measurements were 0.86 (NO₂) and 0.61 (HCHO). The high NO₂ and HCHO concentrations were observed at azimuths of 180° and 315° at heights of 0.8-1.5 km, and they may have been emitted by aircrafts. Importantly, the ratio of HCHO to NO₂ during a typical pollution episode revealed that the factors controlling the O₃ formation changed with altitude: VOCs (surface) to NOx (0.4 km) to transition (1.0 km) to VOCs (1.6 km). Moreover, the effect of VOCs on the O₃ generation was stronger than that of NOx, especially in the downtown area of Hefei. When the ratio of HCHO to NO₂ was 3.55-7.46, the ozone concentration in Hefei could be controlled well, especially at the optimal value of 5.50.

Global Perspective of Drought Impacts on Ozone Pollution Episodes

Ozone (O₃) pollution threatens global public health and damages ecosystem productivity. Droughts modulate surface O₃ through meteorological processes and vegetation feedbacks. Unraveling these influences is difficult with traditional chemical transport models. Here, using an atmospheric chemistry-vegetation coupled model in combination with a suite of existing measurements, we investigate the drought impacts on global surface O₃ and explore the main driving processes. Relative to the mean state, accelerated photochemical rates dominate the surface O₃ enhancement during droughts except for eastern U.S. and western Europe, where reduced stomatal uptakes make comparable contributions. During 1990-2012, the simulated frequency of O₃ pollution episodes in western Europe decreases greatly with a negative trend of -5.5 ± 6.6 days per decade following the reductions in anthropogenic emissions if meteorology is fixed. However, such decreased trend is weakened to -2.1 ± 3.8 days per decade, which is closer to the observed trend of -2.9 ± 1.1 days per decade when year-to-year meteorology is applied because increased droughts alone offset 43% of the effects from air pollution control. Our results highlight that more stringent controls of O₃ precursors are necessary to mitigate the higher risks of O₃ pollution episodes by more droughts in a warming world.

Exploring the causes for co-pollution of O3 and PM2.5 in summer over North China

Co-pollution of surface O₃ and PM_2.5 has become the most predominant type of air pollutions in Beijing-Tianjin-Hebei region in the hot season since 2017, particularly in May-July. Analysis based on observational data showed that co-pollution was always accompanied by high temperature, moderate relative humidity, extremely high SO₂, and higher NO₂. We also found that the meteorology and precursor dependence of O₃ was similar between co-pollution and O₃- single pollution. While PM_2.5 in co-pollution was more related to temperature, relative humidity, and precursors, that in PM_2.5-singe pollution were more related to small winds. These results indicate that co-pollution seemed to be more affected by atmospheric chemistry. According to the PM_2.5 components, secondary inorganic aerosols (SIA) composed 44.3-48.7% of PM_2.5 in co-pollution, while those accounting for 42.1-46.5% and 41.2-44.3%, respectively, in O₃- and PM_2.5-single pollution, which further confirmed the relatively stronger atmospheric chemistry processes in co-pollution. And the high proportion of SIA in co-pollution was mainly attributed to SO₄^2-, which was observed to rapidly boom in non-refractory submicron aerosol (NR-PM₁) on the condition of high level of O₃ at daytime. Additionally, we further explored the interactions of O₃ and PM_2.5 in co-pollution. It was found that most (~61.9%) co-pollution episodes were initiated by high O₃ at daytime; while for other episodes, high PM_2.5 firstly occurred under the more stable meteorological conditions, and then accumulation of precursors further induced high O₃. A higher SIA concentration was observed in O₃-initiated co-pollution, indicating that the atmospheric oxidation in co-pollution caused by chemical processes was stronger than that by physical processes, which was further approved by the higher values of SOR and NOR in O₃-initiated co-pollution. This observational study revealed that controlling O₃ and precursor SO₂ is the key to abating co-pollution in the hot season.

Ozone control strategies for local formation- and regional transport-dominant scenarios in a manufacturing city in southern China

Given the leveling off of fine particulate matter (PM_2.5), ground-level ozone (O₃) pollution has become one of the most significant atmospheric pollution issues in the Pearl River Delta (PRD) region in China, especially in the manufacturing city of Dongguan, which faces more severe O₃ pollution. The development of strategies to control O₃ precursor emissions, including volatile organic compounds (VOCs) and nitrogen oxide (NO_x), depends to a large extent on the source region of the O₃ pollution. In this study, by combining the Weather Research and Forecasting model coupled with chemistry (WRF-Chem), the Empirical Kinetic Modeling Approach (EKMA), and the Flexible Particle model (FLEXPART), more effective strategies of controlling O₃ precursor emissions were identified under two typical types of O₃ pollution episodes: local formation (LF)-dominant (8-12 September 2019) and regional transport (RT)-dominant (23-27 October 2017) episodes, distinguished by the WRF-FLEXPART model. During the LF-dominant episode, the EKMA revealed that the O₃ formation in Dongguan was in a transitional regime, and the abatement of solvent use-VOCs emissions in the key area of Dongguan was more effective in reducing O₃ levels, with an emission reduction benefit 1.7 times that of total VOCs emission sources throughout Dongguan. With respect to the RT-dominant episode, the reduction in VOCs emissions in the local region did not effectively curb O₃ pollution, although the photochemical regime of the O₃ formation in Dongguan was VOCs-limited. A 50% reduction in NO_x emissions in the upwind regions (parts of Guangzhou and Huizhou) effectively decreased the O₃ concentration in Dongguan by 17%. The results of this study emphasize the importance of the source region of O₃ pollution in the implementation of effective O₃ control strategies and provide valuable insights for region-specific precursor emission policy formulation, not only in Dongguan, but also in other regions facing severe O₃ pollution.

Rapid and sensitive online determination of ozone via gas-liquid chemiluminescence synergistically enhanced by graphene quantum dots and Triton X-100

The determination of the ozone concentration in the atmosphere is an urgent need but most current methods are limited by large-scale equipment or complex procedures. Herein, a gas-liquid chemiluminescence (GL-CL) assay based on a portable GL-CL detector platform was reported for the fast and sensitive online determination of ozone. Graphene quantum dots (GQDs) and Triton X-100 were employed to synergistically enhance the CL intensity of chromotropic acid (CA)-ozone. The increase was about seven-fold upon the addition of GQDs and Triton X-100. The potential enhancement mechanism was also investigated. The speculated CL enhancement mechanism was that GQDs could catalyze dissolved oxygen in the CA solution to produce more free radicals in the presence of UV-light, and these radicals converted CA into more active compounds that could react with ozone and emit photons. The free radicals, active compounds and luminophores were protected from water quenching by micelles produced by dissolving Triton X-100 in water and as a result, CL was markedly enhanced. Most importantly, the response time of the GL-CL detector platform towards ozone was less than 0.5 s. Based on this outcome, a GL-CL assay for detecting atmospheric ozone was successfully developed with a linear range from 0.1 to 150 ppbv and a detection limit of 0.02 ppbv. This work provides a rapid and sensitive method for the online measurement of ozone, and has great potential in environmental applications; the potential applications of GQDs and Triton X-100 in the field of GL-CL have also been highlighted.

Vertical Structure of Air Pollutant Transport Flux as Determined by Ground-Based Remote Sensing Observations in Fen-Wei Plain, China

Air pollutant transport plays an important role in local air quality, but field observations of transport fluxes, especially their vertical distributions, are very limited. We characterized the vertical structures of transport fluxes in central Luoyang, Fen-Wei Plain, China, in winter based on observations of vertical air pollutant and wind profiles using multi-axis differential optical absorption spectroscopy (MAX-DOAS) and Doppler wind lidar, respectively. The northwest and the northeast are the two privileged wind directions. The wind direction and total transport scenarios were dominantly the northwest during clear days, turning to the northeast during the polluted days. Increased transport flux intensities of aerosol were found at altitudes below 400 m on heavily polluted days from the northeast to the southwest over the city. Considering pollution dependence on wind directions and speeds, surface-dominated northeast transport may contribute to local haze events. Northwest winds transporting clean air masses were dominant during clean periods and flux profiles characterized by high altitudes between 200 and 600 m in Luoyang. During the COVID-19 lockdown period in late January and February, clear reductions in transport flux were found for NO2 from the northeast and for HCHO from the northwest, while the corresponding main transport altitude remained unchanged. Our findings provide better understandings of regional transport characteristics, especially at different altitudes.

Distinct spatiotemporal variation patterns of surface ozone in China due to diverse influential factors

A better knowledge of surface ozone variations and the relevant influential factors is of great significance for controlling frequent ozone pollution events. In this study, we first examined the primary variation patterns of surface ozone in space and time across China via a clustering analysis on the basis of daily maximum 8h average surface ozone (MDA8) between 2015 and 2018. Statistical models were then established between MDA8 and a set of influential factors to pinpoint dominant factors contributing to regional MDA8 variations. The clustering results revealed four typical variation patterns of MDA8 in China given distinct pollution levels, seasonality, and long-term trends. Statistical modeling results indicated that the seasonal variability of MDA8 was closely associated with UV radiation and meteorological factors like boundary layer height, temperature and relative humidity. In contrast, the long-term trends of MDA8 were largely linked to ozone precursors and meteorological variables including temperature, relative humidity, and total cloud cover. Moreover, the phenomenal increasing trends of MDA8 in North China were found to be statistically associated with the depletion of nitrogen dioxide (NO₂) and carbon monoxide (CO). Specifically, substantial increases in volatile organic compounds (VOCs) along with depletions in NO₂ and CO significantly boosted the photochemical ozone formation chain process in a VOC-limited regime like the North China plain. Overall, the inferred linkage in this study provides evidence and clues to help control increasing ozone pollution events in North China.

Sensitivities of Ozone Air Pollution in the Beijing-Tianjin-Hebei Area to Local and Upwind Precursor Emissions Using Adjoint Modeling

Effective mitigation of surface ozone pollution entails detailed knowledge of the contributing precursors' sources. We use the GEOS-Chem adjoint model to analyze the precursors contributing to surface ozone in the Beijing-Tianjin-Hebei area (BTH) of China on days of different ozone pollution severities in June 2019. We find that BTH ozone on heavily polluted days is sensitive to local emissions, as well as to precursors emitted from the provinces south of BTH (Shandong, Henan, and Jiangsu, collectively the SHJ area). Heavy ozone pollution in BTH can be mitigated effectively by reducing NO_x (from industrial processes and transportation), ≥C₃ alkenes (from on-road gasoline vehicles and industrial processes), and xylenes (from paint use) emitted from both BTH and SHJ, as well as by reducing CO (from industrial processes, transportation, and power generation) and ≥C₄ alkanes (from industrial processes, paint and solvent use, and on-road gasoline vehicles) emissions from SHJ. In addition, reduction of NO_x, xylene, and ≥C₃ alkene emissions within BTH would effectively decrease the number of BTH ozone-exceedance days. Our analysis pinpoint the key areas and activities for locally and regionally coordinated emission control efforts to improve surface ozone air quality in BTH.

Ozone Concentration Levels in Urban Environments-Upper Silesia Region Case Study

Although ozone (O3) plays a crucial role in screening the Earth's surface and lower atmosphere layers from the ultraviolet radiation, troposphere ozone is proven to have negative health effects on the human body and is one of the greenhouse gases. The objective of this study was to perform a measurement-based assessment for determining whether the concentration of ozone is within admissible limits, or exceeded, in Silesia Province and does not pose a threat to the local population. The data provided by the Voivodship Inspectorate for Environmental Protection in Katowice were used in the analysis. The received data constitute the result of 8-h measurements of concentrations of ozone at selected air monitoring stations of the Silesian province. The locations of three monitoring stations were found to be useful for the aim of this research; one site is situated in a rural background area; another one is located in a medium-sized city and the Katowice station is representative for an urban background situation. We used cluster analysis, weighted pair group method using arithmetic averages (WPGMA) and Chebyshev distances to test the hypothesis and compare empirical distributions in the general population. The alarm level has not been exceeded in indicated measurements stations in Silesian Voivodship in the period 2015-2017 (averaging time 1 h: 240 µg/m3 for 3 h). The target level was exceeded in 2015 at all three measurements stations and in the following years at one station (in Zloty Potok, 2016, and in Katowice, 2017). Each year, the largest number of exceedances occurred in August. The results clearly indicate a lack of hazards for the general population's health in terms of increased concentrations of ozone in the city centers and outside. The results confirm that environmental conditions (i.e., landform, the area surrounding monitoring station) have a significant influence on the ozone level.