Near-surface O3 Research Articles

Diurnal hourly near-surface ozone concentration derived from geostationary satellite in China

Near-surface O3 is a harmful atmospheric pollutant and a key component of urban photochemical pollution. The availability of satellite ozone concentration products is predominantly restricted to daytime, resulting in a lack of understanding of nighttime ozone pollution (e.g. nocturnal ozone enhancement events). This research leverages 5-km bright temperatures derived from Advanced Himawari Images (AHI) on the Himawari-8 satellite, in conjunction with auxiliary data, to estimate 24-h near-surface O3 concentrations in China at a resolution of 5 km for 2020. The model achieves an average 5-fold cross-validation R2 of 0.92. Comparative analysis with on-site observations reveals that the model has low relative errors between 8:00 and 21:00 LT. The estimated O3 maps depict a consistent 24-h variation pattern, characterized by high and most fluctuating concentrations during the daytime, reaching a peak around 16:00 LT, which is primarily due to the increased photochemical reactions and the O3 accumulation in the mid-afternoon. In the daytime of summer, high surface ozone concentrations are mainly contributed by June. The elevated levels of O3 are predominantly found in central China, particularly in the Beijing-Tianjin-Hebei region and Inner Mongolia. It can also be seen that although the highest average daytime surface O3 concentration occurs in summer, the highest nighttime concentration is observed in spring, which may be attributed to the frequent occurrence of horizontal transport and vertical mixing of O3. This study holds promise in providing comprehensive round-the-clock surface O3 data across China, thereby enhancing our understanding of diurnal ground-level O3 variations.

A mechanism of stratospheric O3 intrusion into the atmospheric environment: a case study of the North China Plain

Abstract. Stratosphere-to-troposphere transport results in the stratospheric intrusion (SI) of O3 into the free troposphere through the folding of the tropopause. However, the mechanism of SI that influences the atmospheric environment through the cross-layer transport of O3 from the stratosphere and free troposphere to the atmospheric boundary layer has not been elucidated thoroughly. In this study, an SI event over the North China Plain (NCP; 33–40° N, 114–121° E) during 19–20 May 2019 was chosen to investigate the mechanism of the cross-layer transport of stratospheric O3 and its impact on the near-surface O3 based on multi-source reanalysis, observation data, and air quality modeling. The results revealed a mechanism of stratospheric O3 intrusion into the atmospheric environment induced by an extratropical cyclone system. The SI with downward transport of stratospheric O3 to the near-surface layer was driven by the extratropical cyclone system, with vertical coupling of the upper westerly trough, the middle of the northeast cold vortex (NECV), and the lower extratropical cyclone, in the troposphere. The deep trough in the westerly jet aroused the tropopause folding, and the lower-stratospheric O3 penetrated the folded tropopause into the upper and middle troposphere; the westerly trough was cut off to form a typical cold vortex in the upper and middle troposphere. The compensating downdrafts of the NECV further pushed the downward transport of stratospheric O3 in the free troposphere; the NECV activated an extratropical cyclone in the lower troposphere; and the vertical cyclonic circulation governed the stratospheric O3 from the free troposphere across the boundary layer top, invading the near-surface atmosphere. In this SI event, the average contribution of stratospheric O3 to near-surface O3 was accounted for at 26.77 %. The proposed meteorological mechanism of the vertical transport of stratospheric O3 into the near-surface atmosphere, driven by an extratropical cyclone system, could improve the understanding of the influence of stratospheric O3 on the atmospheric environment, with implications for the coordinated control of atmospheric pollution.

Fluctuations in the “static” atmosphere and their effects on tropospheric ozone distribution

Atmospheric fluctuation can be seen everywhere. This study focuses on the record-breaking increase of O3 concentration during the summer in some sensitive areas in recent years. The findings indicate that in the vicinity of the East Asian continent near western Pacific ocean, when the atmospheric conditions are stable or neutral, it is conducive to the maintenance and propagation of atmospheric oscillations near the height of the pollutant mixed layer (H_PML). Accompanied by the "peak-trough" effect of external gravity wave oscillations, due to the abundant water vapor of the cloud system (there are low pressure or typhoon disturbances in summer) near the large-scale cloud belt at the edge of the subtropical high in the western Pacific, the bright temperature at cloud top shows "light and dark changes" on satellite images, forming a wave-like cloud system. The novelty of this study lies in the fact that atmospheric fluctuations near the H_PML is not only related to the known aggravation of heavy rainfall, but also leads to the additional value-added effect of aerosols. Under static atmospheric conditions, the impact of atmospheric fluctuations near the H_PML on additional rise of O3 concentration helps us to deepen our understanding of the so-called "entrained ozone (EZ) effect" in the atmosphere. Due to the external gravity waves, the concentration of O3 increased further. Diurnal variations of solar zenith angle and H_PML are key meteorological factors influencing the significant increase in near-surface O3 concentration entrainment. The formation mechanism of solar photochemical O3 is further deepened and supplemented by analyzing the record-breaking increase of O3 concentration in summer observed in recent years.

Ozone pollution aggravated by mountain-valley breeze over the western Sichuan Basin, Southwest China

The impact of thermally driven mountain-valley breezes (MVB) on the atmospheric environment remains poorly understood, especially in ozone (O3)-polluted regions with complex underlying topography. To address this knowledge gap, we focused on the western Sichuan Basin (SCB), situated immediately east of the Tibetan Plateau (TP), which is considered susceptible to MVB coupled with severe O3 pollution in southwest China. We revealed the MVB driving diurnal O3 variations and meteorological mechanisms using surface observations and ERA5 reanalysis data. Local MVB days accounted for up to 47% of cases in the summers of 2015–2022. Driven by the MVB, the near-surface O3 concentrations increased by 8.8%, with 12.7% and 50.0% deterioration in the O3 light and moderate exceedance rates, respectively, on the western SCB edge. The daytime upslope valley breeze with 20% higher wind speed drove the westward transport of rich O3 and precursors from the upwind-polluted inner SCB towards its western edge, and the O3 photochemical production, followed by intensifying solar radiation and air temperature, gave rise to 14.8% of surface O3 concentrations over the western SCB edge. The nighttime downward mountain breeze with a 20% increase in wind speed could transport the rich O3 in the mountainous area to the basin edge, causing O3 levels to increase by 2.8%. In summary, we quantitatively assessed the impacts of MVB on changes in O3 concentrations and air quality along with its meteorological mechanisms, facilitating a comprehensive understanding of meteorological drivers in the atmospheric environment.

Current scenario of ozone pollution and its influence on population health in China

<p>Ozone (O3) is a secondary pollutant formed by photochemical reactions in the atmosphere, significantly contributing to air pollution, particularly in global cities and economically developed regions. The escalating O3 concentration has emerged as a critical air pollution concern in China. When near-surface O3 surpasses natural levels, it adversely impacts human health. Our understanding of O3 pollution remains limited, partly due to the delayed implementation of atmospheric O3 and its precursors' monitoring. Accordingly, utilizing observed data, this paper assesses the O3 levels in China over the past decade. We found that surface O3 concentrations had consistently risen since 2013, with the only decline noted in 2018. O3 pollution is particularly severe in economically developed areas such as the Beijing-Tianjin-Hebei region, the Yangtze River Delta, the Pearl River Delta, and the Weihe Plain. Chronic exposure to O3 can negatively impact respiratory and cardiovascular systems. By introducing research findings related to O3 exposure and human health, we offer suggestions for future research on human health implications of surface O3 exposure. These findings underscore the importance of O3 as a focal point in China's future air quality policy and highlight the urgent necessity for stricter control of precursor emissions.</p>

Recent-year variations in O3 pollution with high-temperature suppression over central China

By analyzing environmental and meteorological monitoring data over recent years of 2015–2022, the Twain-Hu Basin (THB) in central China was identified as a regional O3 pollution center over China with the highest increasing trend at 1.10 %⸱yr−1 in interannual variations of O3 concentrations with deteriorating O3 pollution over recent years. We explored the spatiotemporal variations in O3 pollution in the THB with ozone suppression (OS) under high air temperature over metropolitan, small urban, and mountainous areas. The bipolarized interannual trends in interannual O3 variations in urban and mountainous areas over central China were characterized with the increasing and decreasing 90th percentiles of the daily maximum 8-h (MDA8-90) O3 concentrations respectively in polluted urban areas and clean mountainous areas over recent eight years. The changes of the near-surface O3 concentrations with air temperature exhibited the inflection points of OS from increasing to decreasing O3 at air temperature of 30.5 °C in mountainous areas, 32.5 °C in small urban areas, and 34.5 °C in metropolitan areas, and the intensity of OS was estimated in the ranking with mountainous areas (−2.30 μg⸱m−3⸱°C−1) > small urban areas (−1.96 μg⸱m−3⸱°C−1) > metropolitan areas (−1.54 μg⸱m−3⸱°C−1), indicating that the OS was more significant over the lower-O3 mountainous areas. This study has implications for understanding O3 pollution variations with the meteorological drivers.

3-D Changes of Tropospheric O3 in Central and Eastern China Induced by Tropical Cyclones over the Northwest Pacific: Recent-Year Characterization with Multi-Source Observations

In this study, the multi-year data of meteorology and O3 from remote sensing and ground observations are applied to characterize the 3-D changes of O3 in the troposphere over central and eastern China (CEC) induced by the tropical cyclones (TCs) in the tropical and subtropical ocean regions over Northwest Pacific. The CEC-regional average of near-surface O3 levels is significantly elevated with 6.0 ppb in the large coverage by the TCs in the subtropical ocean, while the TCs in the tropical ocean alter near-surface O3 weakly, indicating the latitudinal-located TCs in the subtropical offshore ocean could largely influence the O3 variations over CEC. The sub-seasonal change with the positive and negative anomalies of near-surface O3 is induced by the tropical TCs from June to July and from August to October. The peripheral circulation of TCs in the subtropical offshore ocean persistently enhances the O3 concentrations over CEC during the season of East Asian summer monsoons. The positive O3 anomalies maintain from the entire troposphere to the lower stratosphere over CEC in the peripheries of subtropical TCs, while the tropical TCs cause the positive O3 anomalies merely in the lower troposphere. The O3 transport and accumulation, photochemical production and stratospheric intrusion are climatologically confirmed as the major meteorological mechanisms of TCs affecting the O3 variations. This study reveals that the downward transport of stratospheric O3 of TCs in the subtropical ocean exerts a large impact on the atmospheric environment over CEC, while the regional O3 transport and photochemical productions dominate the lower troposphere over CEC with less impact of stratospheric intrusion from the TCs in the tropical ocean region. These results present the climatology of tropospheric O3 anomalies in China induced by the TCs over the Northwest Pacific with enhancing our comprehension of the meteorological impact on O3 variations over the East Asian monsoon region.

Nocturnal ozone enhancement in Shandong Province, China, in 2020–2022: Spatiotemporal distribution and formation mechanisms

Nighttime ozone enhancement (NOE) can increase the oxidation capacity of the atmosphere by stimulating nitrate radical formation and subsequently facilitating the formation of secondary pollutants, thereby affecting air quality in the following days. Previous studies have demonstrated that when nocturnal ozone (O3) concentrations exceed 80 μg/m3, it leads to water loss and reduction of plant yields. In this study, the characteristics and mechanisms of NOE over Shandong Province as well as its 16 cities were analyzed based on observed hourly O3 concentrations from 2020 to 2022. The analysis results show that NOE predominantly occurred in the periods of 0:00–3:00 (41 %). The annual mean frequency of NOE events was ~64 days/year, approximately 4–7 days per month. The average concentration of nocturnal O3 peak (NOP) was ~72.6 μg/m3. Notably, high NOP was observed in the period from April to September with the maximum in June. Coastal cities experienced more NOE events. Typical NOE events characterized by high NOP concentrations in the coastal cities of QingDao, WeiHai and YanTai in June 2021 were selected for detailed analysis with a regional chemical transport model. The results showed that high levels of O3 in eastern coastal cities during NOE events primarily originate from horizontal transport over the sea, followed by vertical transport. During the daytime, O3 and its precursors are transported to the Yellow Sea by westerly winds, leading to the accumulation of O3 near the sea and coastline. Consequently, under the influence of prevailing winds, the movement of O3 pollution belts from the sea to land causes rapid increases in near-surface O3 levels. Meanwhile, vertical transport can also contribute to NOE in coastal areas. The high-level O3 in the upper atmosphere generally originates from long-distance transport and turbulent transport of O3 produced near the ground during the daytime. At night, the absence of chemicals that consume O3 in the upper air and descending air flow carries O3 to the near-surface. The impacts of other O3-depletion processes (such as dry deposition) on NOE are less pronounced than those of transport processes.

Effects of Ozone Stress on Rhizosphere Soil of Poplar Seedlings

Near-surface O3 has negative effects on plant productivity; however there were few studies on the effects of O3 pollution on the belowground part of the ecosystem. The effect of O3 stress on the belowground parts of poplar is unclear. We investigated the effects of O3 pollution on poplar rhizosphere soil in open-top chambers (OTC). Two kinds of plants with different O3 sensitivity were selected, i.e., high-sensitive poplar clone 546 and low-sensitive poplar clone 107. The control group and high-concentration O3 group were set up: charcoal-filtered air, CF; unfiltered air + 60 ppb O3, NF. Poplar rhizosphere soil was taken after 96 days (15 June to 17 September 2020) of cultivation in OTCs. O3 stress decreased the amplicon sequence variations (ASVs) of microorganisms in poplar 107 and poplar 546 rhizosphere soil, with no significant interspecific difference. The effect of O3 fumigation on the fungal community was greater than that on the bacterial community. The correlation between the bacterial community and rhizosphere soil physicochemical indices was closer than that of the fungal community. Some fungi, such as Clitopilus hobsonii, Mortierella sp., and Minimedusa, might help poplar resist the O3 stress. O3 stress had direct impacts on the pH, nutrients, and enzyme activities of rhizosphere soil, while it had indirect negative impacts on microbial community composition by nutrients. There was no difference in sensitivity between rhizosphere soil response to O3 stress of poplar clone 107 and clone 546, which might take a longer accumulation time to show the effect. This study provides a certain basis for accurately evaluating the ecological effects of O3 pollution.

Impacts of projected changes in sea surface temperature on ozone pollution in China toward carbon neutrality

The global sea surface temperatures (SSTs) are expected to change diversely in the future under different climate scenarios, which will affect the near-surface ozone (O3) distribution and concentration by influencing meteorological states and large-scale atmospheric circulation. Many countries have planned to reach carbon neutrality by the mid-21st century. In this study, the impacts of global and regional SST changes on near-surface O3 concentrations in China in the middle of the 21st century under the carbon-neutral scenario (Shared Socioeconomic Pathway 1–1.9), compared with the high-emission scenario (Shared Socioeconomic Pathway 5–8.5), and possible physical and chemical mechanisms are investigated using the Community Earth System Model version 1 (CESM1). Under future climate change, the changes in SSTs in the carbon-neutral scenario relative to the high-emission scenario lead to a dipole change in near-surface O3 concentrations in eastern and western China, with a significant decrease of 0.79 ppbv in the eastern China and a significant increase of 1.05 ppbv in the western China. The cooling of North Pacific Ocean under the carbon-neutral scenario causes a decrease in near-surface O3 concentrations by 0.48 ppbv in eastern China due to the weakened chemical production and an increase by 0.74 ppbv in western China attributed to the enhanced O3 transport from Eurasia. Cooling of Southern Hemisphere oceans leads to anomalous upward air motions over eastern China, which weaken the vertical transport of high-elevation O3 to the surface, resulting in a reduction in near-surface O3 concentrations by 0.58 ppbv in eastern China. Our results suggest that future changes in SSTs in the carbon-neutral scenario will positively benefit O3 air quality improvement in the polluted eastern China, with the North Pacific and Southern Hemisphere oceans playing important roles.

Estimating Daily Concentrations of Near-Surface CO, NO2, and O3 Simultaneously Over China Based on Spatiotemporal Multi-Task Transformer Model

Accurate and efficient estimation of near-surface air pollutant concentrations holds significant practical importance. Current models for estimating near-surface concentrations (NSC) primarily rely on shallow methods and focus on estimating a single pollutant. However, these models face challenges in capturing the complex spatiotemporal patterns of NSC and demonstrate inefficiency. To overcome these limitations, we propose a spatiotemporal multi-task Transformer model (stmtTransformer) to simultaneously estimate the NSC of carbon monoxide (CO), nitrogen dioxide (NO2), and ozone (O3). Estimation experiments conducted in China from 2021 to 2022 demonstrate that stmtTransformer achieves optimal performance by effectively capturing the spatiotemporal variations of NSC. Based on sample-based validation, the R2 values are 0.643 (CO), 0.781 (NO2), and 0.902 (O3), and the RMSE values are 0.194 mg/m3 (CO), 5.613 µg/m3 (NO2), and 13.330 µg/m3 (O3), respectively. In terms of efficiency, stmtTransformer significantly improved the training efficiency by 185.21 % and the estimation efficiency by 129.44 % compared to the single-task model. Finally, when plotting the daily and seasonal maps of NSC for 2022, it is evident that the estimates exhibit a consistent spatial distribution.

Terrain effect on atmospheric process in seasonal ozone variation over the Sichuan Basin, Southwest China

Terrain effect is challenging for understanding atmospheric environment changes under complex topography. This study targets the Sichuan Basin (SCB), a deep basin isolated by plateaus and mountains in Southwest China, by employing WRF-Chem with integrated process rates (IPR) analysis to characterize the terrain-driven seasonal variations of tropospheric ozone (O3) with atmospheric physical and chemical processes. Results show that the basin terrain exerts reversed impacts on regional air quality changes by aggravating summertime and alleviating wintertime near-surface O3 with the relative contributions oscillating seasonally between −40% and 40% in SCB. Similarly, a seasonal shift of vertical O3 structures is dominated by summertime positive and wintertime negative changes in the lower troposphere induced by basin terrain. The key contributions of atmospheric process to near-surface O3 are identified with vertical and horizontal transport, which is dominated by basin terrain with intensifying seasonal and diurnal variations. With the existence of basin, the daytime O3 productions at the near-surface layer are elevated in months of warm seasons (April and July) but inhibited in the cold seasons (October and January), presenting a seasonal transition of primary factor from meteorology to aerosol-radiation forcing on photochemical reactions. Driven by plateau-basin thermodynamic forcing, horizontal O3 transport between the SCB and eastern TP is enhanced by mountain-plains solenoid (MPS), and even nocturnal O3-rich layers contribute to the impacts of vertical exchange on near-surface O3 levels. The terrain effects of deep basin under the interaction of Asian monsoons and westerlies could jointly change atmospheric physical and chemical processes to construct the seasonal and diurnal O3 evolution patterns over the SCB region.

Impacts of urban expansion on meteorology and air quality in North China Plain during wintertime: A case study

The North China Plain (NCP) is one of the areas with a fast urbanization rate. The proportion of urban areas has increased from 1.78% in 2000 to 6.70% in 2015 in the NCP. Urban expansion induce variations in air pollutants are mainly determined by changes in meteorological conditions and atmospheric physicochemical processes. A persistent severe wintertime particulate pollution episode is simulated using the WRF-Chem model to investigate the impacts of land use/cover change on air quality in the NCP. Sensitivity simulations demonstrated that the urban expansion increases the near-surface temperature by approximately 0.2 °C, and further the development of the planetary boundary layer height by approximately 1.6%, but decreases the relative humidity by 0.4% on average. The near-surface O3 concentrations are increased by 2.2%, but the PM2.5 concentrations are decreased by 2.4% on average in the NCP. The near-surface concentration of NO2, SO2, and CO decrease by 4.5%, 2.2%, and 2.7%, respectively. The decrease in PM2.5 concentrations is approximately 8.9% in urban areas. Although urban expansion increases anthropogenic emissions of air pollutants, it alleviates particulate pollution to some degree, particularly in urban areas.

Maximizing ozone control by spatial sensitivity-oriented mitigation strategy in the Pearl River Delta Region, China

The Pearl River Delta (PRD) has long been plagued by severe O3 pollution, particularly during the autumn. A regional O3 pollution episode influenced by the Western Pacific Subtropical High in September 2021 was characterized by near-surface O3 escalation due to strong photochemical reactions within the planetary boundary layer. This event was targeted to develop effective control strategies through investigation of precursor control type and scope based on the high-order decoupled direct method (HDDM) and integrated source apportionment method (ISAM) of CMAQ. Generally, the majority of areas (67.0 %) were under NOx-limited regime, which should strengthen afternoon NOx control inferred by positive convex O3 responses. However, high emission and heavily polluted areas located in central PRD were under VOC-limited regime (11.6 %) or mixed regime (15.0 %). The remaining areas (6.4 %) were under NOx-titration or insensitive conditions. Regarding source apportionment, Guangdong province contributed 32.3 %–58.4 % to MDA8 O3 of PRD, especially higher proportion (>50 %) to central areas. Overall, local-focused NOx/VOC emission reductions had limited effects on O3 mitigation for receptor cities compared to regional-cooperative regulation. When region-wide VOC emission reduction was implemented, MDA8 O3 in VOC-limited grids exhibited the largest declines (2.3 %–4.1 %, 3.9– 7.0 μg·m−3). However, unified NOx control contributed to increasing MDA8 O3 in VOC-limited grids (most stations located for air quality evaluation) whereas decreased MDA8 O3 by 2.1 %– 5.7 %, 3.0– 8.2 μg·m−3 in large-scale NOx-limited grids. The sensitivity-oriented regional control avoided O3 rebound and achieved the greatest decline of 3.4 %– 5.0 %, 5.7– 8.4 μg·m−3 in VOC-limited grids; additionally, time-refined dynamic aggressive NOx control decreased peak O3 by an extra 1.2– 6 μg·m−3, both of which facilitate the regulation for the forecasting O3 episodes. These findings suggest that in heavily polluted environments, the enhancement of O3 regulation benefits requires meticulous, coordinated, and dynamic NOx and VOC controls spanning the entire region based on high-resolution analysis of heterogeneous O3-NOx-VOC sensitivity. Furthermore, emission reduction gains should be more reasonably reflected through increasing in-situ observations covering multi-sensitivity regions.

Spatiotemporal modeling of air pollutant concentrations in Germany using machine learning

Abstract. Machine learning (ML) models are becoming a meaningful tool for modeling air pollutant concentrations. ML models are capable of learning and modeling complex nonlinear interactions between variables, and they require less computational effort than chemical transport models (CTMs). In this study, we used gradient-boosted tree (GBT) and multi-layer perceptron (MLP; neural network) algorithms to model near-surface nitrogen dioxide (NO2) and ozone (O3) concentrations over Germany at 0.1∘ spatial resolution and daily intervals. We trained the ML models using TROPOspheric Monitoring Instrument (TROPOMI) satellite column measurements combined with information on emission sources, air pollutant precursors, and meteorology as feature variables. We found that the trained GBT model for NO2 and O3 explained a major portion of the observed concentrations (R2=0.68–0.88 and RMSE=4.77–8.67 µg m−3; R2=0.74–0.92 and RMSE=8.53–13.2 µg m−3, respectively). The trained MLP model performed worse than the trained GBT model for both NO2 and O3 (R2=0.46–0.82 and R2=0.42–0.9, respectively). Our NO2 GBT model outperforms the CAMS model, a data-assimilated CTM but slightly underperforms for O3. However, our NO2 and O3 ML models require less computational effort than CTM. Therefore, we can analyze people's exposure to near-surface NO2 and O3 with significantly less effort. During the study period (30 April 2018 and 1 July 2021), it was found that around 36 % of people lived in locations where the World Health Organization (WHO) NO2 limit was exceeded for more than 25 % of the days during the study period, while 90 % of the population resided in areas where the WHO O3 limit was surpassed for over 25 % of the study days. Although metropolitan areas had high NO2 concentrations, rural areas, particularly in southern Germany, had high O3 concentrations. Furthermore, our ML models can be used to evaluate the effectiveness of mitigation policies. Near-surface NO2 and O3 concentration changes during the 2020 COVID-19 lockdown period over Germany were indeed reproduced by the GBT model, with meteorology-normalized near-surface NO2 having significantly decreased (by 23±5.3 %) and meteorology-normalized near-surface O3 having slightly increased (by 1±4.6 %) over 10 major German metropolitan areas when compared to 2019. Finally, our O3 GBT model is highly transferable to neighboring countries and locations where no measurements are available (R2=0.87–0.94), whereas our NO2 GBT model is moderately transferable (R2=0.32–0.64).

Chemical kinetics of near-surface ozone at a suburban location in India

The spatial gradient in near-surface ozone (O3) is controlled by its production, sink, and net transport (advection/convection and diffusive) in the atmosphere. In this work, we used continuous long-term measurements of O3, oxides of nitrogen (NOx = NO + NO2), and meteorological data in the suburban location of Shadnagar, India. Data analyses were performed to investigate the governing processes that control O3 variability on diurnal and seasonal time scales. The role of chemistry in O3 variability, including both formation and destruction processes, was investigated using known chemical kinetics and a radiative transfer model. The residual between observations and chemical estimation was further analyzed to examine the role of transport and unresolved processes/uncertainty in the dataset. The O3 residual was duly validated using model reanalysis data of O3 and meteorological parameters to further estimate the O3 transport. Our analyses show that the average net production and net transport of near-surface O3 are 3.18 and 0.87 ppbv/h, respectively, while horizontal advection is 0.01 ppbv/h in the daytime. The production of ozone was found to be dominant, indicating the influx of ozone at the site. Overall, our results highlight that spatio-temporal variability in near-surface ozone is strongly controlled by net production in Shadnagar and may be applicable in similar environments globally.

An assessment of O3-related health risks and economic losses in typical regions of China.

As one of the key areas for air pollution prevention and control in China, the Fenwei Plain is experiencing serious near-surface O3 pollution, which is a key issue that needs to be solved urgently. Based on pollutant concentration monitoring data and meteorological and health data over the same period, this study analyzed the temporal and spatial characteristics, the relationships with meteorological factors of O3 pollution, and the health effects and economic losses caused by exposure to O3 pollution using environmental health risk and environmental value assessment methods in 11 cities on the Fenwei Plain in China from 2014 to 2020. The results showed that O3 pollution has become increasingly serious on the Fenwei Plain in recent years. The annual average concentration of O3_8h_max showed an overall upwards trend, with an increase of 32.39% in 2020 compared to 2014. The mean concentrations observed in summer were the highest, followed by spring and autumn, and the lowest was in winter. The O3 concentration had a significant positive correlation with air temperature and sunshine hours. The evaluation results of the impact of air pollution on population health showed that the number of premature deaths caused by O3 pollution fluctuated and increased during 2014-2020. In 2020, the numbers of total, cardiovascular and respiratory deaths attributable to O3 pollution on the Fenwei Plain were 6,867 (95% CI: 3,739-9,965), 3,652 (95% CI: 1,363-5,905), and 1,257 (95% CI: 747-2,365), respectively, and the total number of premature deaths related to O3 exposure increased by 48.05% compared with 2014. The health and economic losses attributed to O3 pollution on the Fenwei Plain during the study period were 44.22 (95% CI: 22.17-69.18), 47.16 (95% CI: 23.64-73.77), 68.28 (95% CI: 34.27-106.31), 114.44 (95% CI: 57.42-177.76), 110.85 (95% CI: 55.45-172.52), 116.41 (95% CI: 58.24-180.74), and 116.81 (95% CI: 58.00-180.88) billion yuan, respectively. In Linfen City, the increasing rate of the number of premature deaths reached 283.39% because the O3 concentration increased greatly. Due to high O3 concentrations and obvious population growth in Xi'an, the problems of premature death and health and economic losses attributed to O3 concentrations exceeding the standard value are prominent.

Rebuilding high-quality near-surface ozone data based on the combination of WRF-Chem model with a machine learning method to better estimate its impact on crop yields in the Beijing-Tianjin-Hebei region from 2014 to 2019

In recent years, the problem of surface ozone pollution in China has been of great concern. According to observation data from monitoring stations, the concentration of near-surface ozone (O3) in China has gradually increased in recent years, and ozone concentration often exceeds the contaminant limit standard, especially in the Beijing-Tianjin-Hebei (BTH) region. High O3 concentration pollution will adversely affect crop growth, which can cause crop yield losses. Therefore, it is urgent to recognize the situation of ozone pollution in the BTH region and quantitatively evaluate the crop yield losses caused by ozone pollution to develop more effective pollution prevention and control policies. However, the monitoring of ozone concentration in China started relatively late compared with some developed countries, and currently, long-time series data covering the BTH region cannot be obtained, which makes it difficult to evaluate the impact of ozone on crop yield. Therefore, a new method (WRFC-XGB) was proposed in this study to establish a high-precision near-surface O3 concentration dataset covering the whole BTH region from 2014 to 2019 by integrating the Weather Research and Forecasting with Chemistry (WRF-Chem) model with the extreme gradient boosting (XGBoost) machine learning algorithm. Through verification with ground observation station data, the results of WRFC-XGB are satisfactory, and R2 can reach 0.78–0.91. Compared with other algorithms, the accuracy of the near-surface ozone concentration dataset is greatly improved, which can be used to estimate the impact of surface ozone on crop yield. Based on this dataset, the yield loss of winter wheat, rice, and maize caused by O3 pollution was estimated by using the response equation of the relative yield and ozone dose index. The results showed that the total yield losses of winter wheat, rice and maize from 2014 to 2019 were 2659.21 million tons, 49.23 million tons and 1721.56 million tons due to ozone pollution in the BTH region, respectively, and the highest relative yield loss of crops caused by O3 pollution could be 29.37% during 2014–2019, which indicated that the impact of ozone pollution on crop yield cannot be ignored, and effective measures need to be developed to control ozone pollution, prevent crop production loss, and ensure people's food security.

Analysis of Causes and Sources of Summer Ozone Pollution in Rizhao Based on CMAQ and HYSPLIT Models

As a typical coastal city, O3 pollution in Rizhao has become increasingly serious in recent years. In order to explore the causes and sources of O3 pollution, IPR process analysis and ISAM source tracking tools based on the CMAQ model were used, respectively, to quantify the contributions of different physicochemical processes and different source tracking areas to O3 in Rizhao. Additionally, by comparing the differences between O3-exceeding days and non-exceeding days, combined with the HYSPLIT model, the regional transportation path of O3 in Rizhao was explored. The results showed that the concentrations of O3, NOx, and VOCs near the coastal areas of Rizhao and Lianyungang were significantly increased on O3 exceedance days compared with those on non-exceedance days. This was mainly because Rizhao was the convergence zone of western, southwestern, and eastern winds on exceedance days, which facilitated the transport and accumulation of pollutants. Process analysis showed that the transport process (TRAN) contribution to the near-surface O3 near the coastal areas of Rizhao and Lianyungang increased significantly on the exceedance days, whereas the contribution to most areas to the west of Linyi decreased. Photochemical reaction (CHEM) had a positive contribution to the O3 concentration in Rizhao during the daytime at all heights, and TRAN had a positive contribution at 0-60 m above the ground, and mainly had a negative contribution above 60 m. The contributions of CHEM and TRAN at 0-60 m above the ground would increase significantly on exceedance days, which was approximately twice that on the non-exceedance days. Source analysis showed that the local sources in Rizhao were the main contribution sources of NOx and VOCs, with the contribution rates of 47.5% and 58.0%, respectively. O3 mainly came from the contribution outside the simulation area (67.5%). The O3 and precursor contributions of the western cities of Rizhao (Weifang, Linyi, etc.) and the southern cities (Lianyungang, etc.) would increase significantly on the days of exceeding the standard. The transportation path analysis showed that the number of exceedances accounted for the largest proportion (11.8%) in the path from the west of Rizhao, which was the main transportation channel of O3 and precursors in Rizhao. This was verified through process analysis and source tracking results, and such trajectories accounted for 13.0% of the total number of trajectories, and their main routes were in the Shaanxi, Shanxi, Hebei, and Shandong regions.

Meteorological impacts on interannual anomalies of O3 import over Twain-Hu Basin

Prominent O3 pollution over Twain-Hu Basin (THB) is observed during 2014–2020, with the annual concentrations of near-surface O3 in the range of 49–65 μg·m−3, larger than those in Sichuan Basin (SCB) and Pearl River Delta (PRD) in China. The increasing rate of O3 over THB (1.9 μg·m−3·yr−1) is also higher than the counterparts in Yangtze River Delta (YRD), SCB and PRD. Besides, the exceeding rate of O3 levels in THB rises from 3.9 % in 2014 to 11.5 % in 2019, greater than those in SCB and PRD as well. Based on the GEOS-Chem simulations in summer over 2013–2020, we find that nonlocal O3 contributes dominantly to THB, with YRD being its principle source region, during regional O3 transport over the central and eastern China. Here, the imported O3 in THB is found to be mainly driven by the wind fields and the windward topography. The East Asia Summer Monsoon (EASM) circulations significantly regulate the interannual anomalies of imported O3 over THB. In the years with abnormally higher O3 import over THB, the EASM weakens, and the location of Western Pacific Subtropical High tends to more eastward compared with the years with abnormally lower O3 import. Particularly, an abnormal easterly winds at the surface of YRD region effectively favor the delivery of O3 from YRD to THB. In addition, the weak EASM promotes and undermines the regional transport of O3 from NCP and PRD to THB, respectively. Correspondingly, the O3 concentrations over THB can be fluctuated greatly depending on the degree of regional O3 transport regulated by the EASM circulations, which indicates a complex relationship between sources and receptors of O3 transport for air quality improvement.