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Elevated ozone (O 3 ) has emerged as the major air quality concern since China's clean air actions, offsetting the health benefits gained from improved air quality. Given the shifted ozone chemical regimes and recently boosted extreme weather in China, it's essential to rethink the O 3 trends since 2013 for evaluations of air pollution mitigation policy. Here, we examine the anthropogenically and meteorologically modulated summertime O 3 trends across China at different stages of the clean air actions using multi-source observations combined with multi-model calculations. Ozone increases steadily in China between 2013-2022, with a fast increase rate of 4.4 μg m -3  yr -1 in Phase I and a much smaller 0.6 μg m -3  yr -1 in Phase II of Action Plan. Results highlight that the deteriorative O 3 pollution in Phase I and early Phase II is dominated by the nonlinear O 3 -emission response. Persistent decline in O 3 precursors has shifted its chemical regime in urban areas and began to show a positive influence on ozone mitigation in recent years. Meteorological influence on O 3 variations is minor until 2019 (∼10%), but it greatly accelerates or relieves the O 3 pollution after then, showing comparable contribution to emissions. Epidemiological model predicts totally 0.8-3.0 thousand yr -1 more deaths across China with altered anthropogenic emissions since clean air actions, and additional health burdens by -1.5-0.3 thousand yr -1 from perturbated meteorology. This study calls for stringent emission control and climate adaptation strategies to attain the ozone pollution mitigation in China., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Purpose of Review: The increasing prevalence of cardiometabolic risk factors (CRFs) contributes to the rise in cardiovascular disease. Previous research has established a connection between air pollution and both the development and severity of CRFs. Given the ongoing impact of air pollution on human health, this review aims to summarize the latest research findings and provide an overview of the relationship between different types of air pollutants and CRFs., Recent Findings: CRFs include health conditions like diabetes, obesity, hypertension etc. Air pollution poses significant health risks and encompasses a wide range of pollutant types, air pollutants, such as particulate matter (PM), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), and ozone (O 2 ). More and more population epidemiological studies have shown a positive correlation between air pollution and CRFs. Although various pollutants have diverse effects on specific cellular molecular pathways, their main influence is on oxidative stress, inflammation response, and impairment of endothelial function. More and more studies have proved that air pollution can promote the occurrence and development of cardiovascular and metabolic risk factors, and the research on the relationship between air pollution and CRFs has grown intensively. An increasing number of studies are using new biological monitoring indicators to assess the occurrence and development of CRFs resulting from exposure to air pollution. Abnormalities in some important biomarkers in the population (such as homocysteine, uric acid, and C-reactive protein) caused by air pollution deserve more attention. Further research is warranted to more fully understand the link between air pollution and novel CRF biomarkers and to investigate potential prevention and interventions that leverage the mechanistic link between air pollution and CRFs., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Carbon neutrality objectives affect meteorology and ozone (O 3 ) concentration in China, both of which would influence crop yields, thus food security. However, the joint impact of these two factors on crop yields in China is not clear. In this study, we investigated future trends in China's maize, rice, soybean, and wheat yields under a carbon-neutral scenario considering both regional emission reduction and global climate change in 2060. By combining a process-based crop model (Agricultural Production Systems sIMulator, APSIM) with O 3 exposure equations, the impacts of regional emission reduction and global climate change were studied. The results suggest that regional emission reduction dominated the increase in yield by reducing the O 3 concentration, whereas global climate change led to yield loss mainly through meteorological factors. The national yield decreases for the four crops ranged from 1.0% to 38.0% owing to meteorological factors, while O 3 reduction resulted in additional yield increases ranging from 2.8% to 7.0%. The combined effect of carbon neutrality, which included both meteorological factors and O 3 concentration, resulted in changes to the yields of maize, rice, soybean, and wheat of +4.3%, -7.3%, -24.0%, and -31.7%, respectively. It seems that crop production loss caused by meteorological factors in 2060 would be mitigated by the O 3 reduction. Given the advantages of declining O 3 concentration, regional emission reduction would likely benefit crop growth. However, global climate change may offset the benefits and threaten food production in China. Therefore, more strict emission reduction policies and global climate change mitigation actions are necessary to ensure food security in China., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Tropical cyclones (TCs) are synoptic-scale systems with a diameter of up to 2000 km, and may persist for several days to weeks. They can significantly affect the atmospheric conditions and ozone (O 3 ) concentrations in coastal areas. They also induce stratospheric intrusion (SI, the injection of stratospheric O 3 into the troposphere) by changing the height of the tropopause. Focusing on the Yangtze River Delta (YRD) region, a highly urbanized coastal area with severe O 3 pollution, we systematically analyze the characteristics of O 3 pollution and SIs as well as their connections under the influence of tropical cyclone Ampil. Based on surface observations, 120-h backward trajectories and ERA5 reanalysis meteorological data, the urban O 3 pollution affected by tropical cyclone Ampil mainly resulted from active photochemical reactions inside the boundary layer and poor diffusion conditions characterized by weak winds. SIs induced by tropical cyclone Ampil were important for the upper and middle troposphere, where O 3 concentration could increase up to 180 ppbv. But they hardly reached the ground over the YRD. Therefore, there was no direct connection between O 3 pollution and SIs. However, the location of SIs can predict urban O 3 pollution. SIs moved with tropical cyclone Ampil but appeared on the northwest side of Ampil, usually 500-1000 km away from tropical cyclone Ampil center. At 200 hPa, they corresponded to a high-PV (>2 PVU) air mass rich in O 3 (>200 ppbv). Below this stratospheric PV signature, urban O 3 concentration was usually high., Competing Interests: Declaration of competing interest The contact author has declared that neither they nor their co-authors have any competing interests., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The relation of acute fluctuations of air pollution to hospital admission for bronchiectasis remained uncertain, and large-scale studies were needed. We collected daily concentrations of particulate matter (PM), sulfur dioxide (SO 2 ), nitrogen dioxide (NO 2 ), carbon monoxide (CO), ozone (O 3 ), and daily hospitalizations for bronchiectasis for 21 cities across Guangdong Province from 2013 through 2017. We examined their association using two-stage time-series analysis. Our analysis was stratified by specific sub-diagnosis, sex and age group to assess potential effect modifications. Relative risks of hospitalization for bronchiectasis were 1.060 (95%CI 1.014-1.108) for PM 10 at lag0-6, 1.067 (95%CI 1.020-1.116) for PM 2.5 at lag0-6, 1.038 (95%CI 1.005-1.073) for PM coarse at lag0-6, 1.058 (95%CI 1.015-1.103) for SO 2 at lag0-4, 1.057 (95%CI 1.030-1.084) for NO 2 at lag0 and 1.055 (95%CI 1.025-1.085) for CO at lag0-6 per interquartile range increase of air pollution. Specifically, acute fluctuations of air pollution might be a risk factor for bronchiectasis patients with lower respiratory infection but not with hemoptysis. Patients aged ≥65 years, and female patients appeared to be particularly susceptible to air pollution. Acute fluctuations of air pollution, particularly PM may increase the risk of hospital admission for bronchiectasis exacerbations, especially for the patients complicated with lower respiratory infection. This study strengthens the importance of reducing adverse impact on respiratory health of air pollution to protect vulnerable populations., (Copyright © 2020 Elsevier GmbH. All rights reserved.)

Severe ozone (O 3 ) pollution in China has magnified global concerns over the past years. Exploring the synoptic impacts and quantifying the source contributions are important for mitigating O 3 pollution. This study focuses on the summertime O 3 pollution over the Yangtze River Delta (YRD) in eastern China. We identify six predominant synoptic weather patterns (SWPs) over the YRD during 2013-2017 using the self-organising map (SOM) approach. We conduct O 3 source attribution based on ozone source apportionment technology (OSAT) in a regional transport model. Surface O 3 pollution is found to be sensitive to the predominant SWPs, including four O 3 -polluted types (northeasterly, northerly and southwesterly and anticyclone) and two O 3 -clean types (cyclone and the Meiyu front). The integrated influences of local chemistry and regional transport are important in O 3 pollution under different SWPs. Daily maximum 8-h average (MDA8) O 3 holds strong negative and positive correlations with relative humidity and sunshine duration, respectively. Among the six SWPs, the concentration and exceedance of MDA8 O 3 reach their maxima under the northerly type on a regional average. Higher O 3 levels, particularly under the northerly and northeasterly types, are primarily related to regional transport on various spatial scales. Local production accounts for the largest proportion of O 3 sources under the anticyclone type. Under the southwesterly type, favourable weather conditions superimposed on regional transport lead to severe O 3 pollution in coastal cities. The impact of super-regional transport is most pronounced along the eastern coast under the cyclone type. Source category analysis shows that transportation and industrial emissions play a prime role in surface O 3 formation. This study illustrates the imperative implementation of joint emission control over eastern China to reduce O 3 pollution., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Future climate change can impact ozone concentrations by changing regional meteorological factors related to ozone (O 3 ) pollution. To better understand the variations of meteorological factors and their effects on O 3 formation processes under future climate conditions, we model the present and the future meteorology and air quality in summer over the Yangtze River Delta (YRD) region by using the Weather Research and Forecasting Model with Chemistry module (WRF/Chem), which is driven by the outputs of Community Climate System Model version 4 (CCSM4). The simulations predict that solar radiation, 2-m air temperature, and wind speed increase in the daytime over most of the YRD region. Absolute humidity and precipitation increase in the north and decrease in the south, while the planetary boundary layer height (PBLH) has an opposite change pattern displaying a decrease in the north and an increase in the south. The southerly wind will be strengthened in the daytime. At night, the change patterns of the meteorological factors are similar to the daytime but with small variations. Meanwhile, O 3 and its precursors all increase in the north and decrease in the south. The increases of NO x , volatile organic compounds (VOC), and CO are related with the decreases of PBLH and the input effect of stronger southerly wind, while the decreases are attributed to the output effect of the stronger southerly wind. During the daytime, the increase of surface O 3 in the north is dominated by the chemical processes related with the increases of solar radiation, air temperature, and O 3 precursors. The decrease of surface O 3 in the south is mainly caused by the transport process changing with the strengthened southerly wind. At night, the surface O 3 changing the amplitude is less than the daytime. The less O 3 variations at night can be attributed to an O 3 titration reaction with NO, the changes in NO x concentrations, and the increases of nocturnal PBLH. With the aid of H 2 O 2 /HNO 3 , O 3 formation in the YRD region is found to be easily affected by NO x in the future. The findings can help to understand the changing trend of O 3 in the YRD region and can propose reasonable pollution control policies.

To improve our understanding of the interplay among local and regional photochemical pollutants in the typical city of the Yangtze River Delta (YRD) region, the concurrent observation of O3 and NOx concentrations at an urban and a suburban site in Nanjing during 2008 is presented. In general, the annual mean O3 concentration is 2.35ppbv lower in the downtown than at suburban due to higher NOx pollution levels correlated with heavy traffic. At both sites, O3 shows a distinct seasonality with the spring maximum and the winter minimum, while the minimum concentration of NOx appears in summertime. Besides the chemical processes of O3 sensitivity in the daytime and the NOx titration at night, meteorological conditions also play an essential role in these monthly and diurnal variations. The ozone weekend effect that can be attributed to the weekly routine of human activities is observed in the urban atmosphere of Nanjing as well, with O3 concentrations 2.09ppbv higher and NOx concentrations 6.20ppbv lower on weekends than on weekdays. The chemical coupling of NO, NO2 and O3 is investigated to show that the OX-component (O3 and NO2) partitioning point occurs at about 35ppbv for NOx, with O3 being the dominant form at lower levels and NO2 dominating at higher levels. And it is also discovered that the level of OX is made up of two contributions, including the regional contribution affected by regional background O3 level and the local contribution correlated with the level of primary pollution. The diurnal peak of regional contribution appears 2-5h after the peak of local contribution, implying that OX in Nanjing might prominently affected by the pollutants from a short distance. The highest regional contribution and the second highest local contribution lead to the spring peak of O3 observed in Nanjing, whereas the highest local contribution and the moderate regional contribution make the O3 concentrations in summer higher than those in autumn and winter. Our results reveal the important environment impacts from meteorological conditions and human activities in the YRD region, and can help to understand O3 pollution in these polluted areas by just using the conventional observations., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The interactions between the terrestrial biosphere, atmospheric chemistry, and climate involve complex feedbacks that have traditionally been modeled separately. We present a new framework that couples the Yale Interactive terrestrial Biosphere (YIBs) model, a dynamic plant-chemistry model, with the RegCM-Chem model. RegCM-Chem–YIBs integrates meteorological variables and atmospheric chemical composition from RegCM-Chem with land surface parameters from YIBs. The terrestrial carbon flux calculated by YIBs is fed back into RegCM-Chem interactively, thereby representing the interactions between fine particulate matter (PM 2.5), ozone (O 3), and carbon dioxide (CO 2). For testing purposes, we carry out a 1-year simulation (2016) at a 30 km horizontal resolution over East Asia with RegCM-Chem–YIBs. The model accurately captures the spatio-temporal distribution of climate, chemical composition, and ecological parameters. In particular, the estimated O 3 and PM 2.5 are consistent with ground observations, with correlation coefficients (R) of 0.74 and 0.65, respectively. The simulated CO 2 concentration is consistent with observations from six sites (R ranged from 0.89 to 0.97) and exhibits a similar spatial pattern when compared with carbon assimilation products. RegCM-Chem–YIBs produces reasonably good gross primary productivity (GPP) and net primary productivity (NPP), showing seasonal and spatial distributions consistent with satellite observations, and mean biases (MBs) of 0.13 and 0.05 kg C m -2 yr -1. This study illustrates that RegCM-Chem–YIBs is a valuable tool to investigate coupled interactions between the terrestrial carbon cycle, atmospheric chemistry, and climate change at a higher resolution on a regional scale. [ABSTRACT FROM AUTHOR]

Despite the implementation of the Clean Air Action Plan by the Chinese government in 2013, the issue of increasing surface ozone (O 3) concentrations remains a significant environmental concern in China. In this study, we used an improved regional climate–chemistry–ecology model (RegCM-Chem-YIBs) to investigate the impact of anthropogenic emissions, meteorological factors, and CO 2 changes on summer surface O 3 levels in China from 2008 to 2018. Compared to its predecessor, the model has been enhanced concerning the photolysis of O 3 and the radiative impacts of CO 2 and O 3. The investigations showed anthropogenic emissions were the primary contributor to the O 3 increase in China, responsible for 4.08–18.51 ppb in the North China Plain. However, changed meteorological conditions played a crucial role in decreasing O 3 in China and may have a more significant impact than anthropogenic emissions in some regions. Changed CO 2 played a critical role in the variability of O 3 through radiative forcing and isoprene emissions, particularly in southern China, inducing an increase in O 3 on the southeast coast of China (0.28–0.46 ppb) and a decrease in southwest and central China (- 0.51 to - 0.11 ppb). Our study comprehensively analyzed O 3 variation across China from various perspectives and highlighted the importance of considering CO 2 variations when designing long-term O 3 control policies, especially in high-vegetation-coverage areas. [ABSTRACT FROM AUTHOR]

Ozone is a phytotoxic pollutant that could damage the vegetation growth and lead to complicated impacts on air quality through meteorological and biogeochemical feedbacks. This study implements a semi‐empirical parameterization regarding the impacts of ozone exposure on photosynthesis rate and stomatal resistance into the Noah‐Multi‐parameterization (Noah‐MP) dynamic vegetation module of Weather Research and Forecasting with Chemistry (WRF/Chem) model. The gaseous dry deposition and biogenic emission algorithms are also coupled with Noah‐MP to enable the ozone‐vegetation coupling. This model reproduces the near‐surface meteorology, air pollutants and vegetation physiology in China, with a spatial correlation coefficient more than 0.9 and normalized mean bias from −0.19 to 0.42. The optimized model also improves the simulations of vegetation physiology (e.g., a reduction of model error by 18%–32%) and ozone dry deposition velocity. The elevated ozone damages plant photosynthesis, and decreases the national gross primary productivity (−28.85%) and leaf area index (−17.41%). The plant transpiration and surface heat flux, as well as air temperature (e.g., up to +0.16°C in summer) and other associated meteorological variables are also altered, finally contributing to 0.49 μg m−3 increase of surface ozone. Otherwise, the suppressed vegetation LAI and biogenic emissions, as well as the lower dry deposition velocity in response to the ozone‐vegetation coupling contribute to the remaining ozone changes by −1.07 μg m−3 and 1.18 μg m−3, jointly constituting the complicated ozone‐vegetation feedbacks on air quality. Our results highlight the necessity of including the ozone‐vegetation coupling in models for reliable prediction of regional climate and air quality. Plain Language Summary: Vegetation controls the land‐atmosphere carbon/water cycle and material exchange, and is thus important in global/regional climate and atmospheric environment. Chronic exposure to ozone could damage the vegetation growth and lead to complicated impacts on regional climate and air quality. This study considers the impacts of ozone exposure on plant photosynthesis and stomata using a semi‐empirical parameterization into the WRF/Chem‐Noah‐MP regional meteorology‐chemistry‐vegetation coupled model. The model well reproduces the near‐surface meteorology, air pollutants and vegetation characteristics in China, with moderate model improvements due to the optimized dynamic vegetation and dry deposition modules. The elevated ozone damages plant photosynthesis and decreases the national gross primary productivity (−28.85%) and leaf area index (−17.41%). Otherwise, the plant transpiration and surface heat flux, as well as air temperature (e.g., up to +0.16°C in summer) and other associated meteorological variables are also altered. The meteorological changes, along with the suppressed biogenic emissions from vegetation and lower dry deposition velocity due to the ozone‐vegetation damage jointly constitute the complicated ozone‐vegetation feedbacks on air quality and contribute to an average of −1.1∼1.2 μg m−3 surface ozone change. Our results highlight the necessity of including the ozone‐vegetation coupling for reliable model predictions. Key Points: The optimized model with ozone‐vegetation coupling improves the simulations of vegetation physiology and dry deposition velocity in ChinaThe O3‐damaged photosynthesis and stomatal conductance could affect regional meteorology, finally contributing to surface ozone increaseThe ozone‐vegetation coupling constitutes complex feedbacks on ozone itself by altered meteorology, biogenic emissions and dry deposition [ABSTRACT FROM AUTHOR]

The rapid urbanization in China is accompanied by increasingly serious air pollution. Particulate matter and ozone are the main air pollutants, and the study of their vertical distribution and correlation plays an important role in the synergistic air pollution control. In this study, we performed Lidar- and UAV-based observations in spring in Nanjing, China. The average concentrations of surface ozone and PM2.5 during the observation period are 87.78 µg m−3 and 43.48 µg m−3, respectively. Vertically, ozone reaches a maximum in the upper boundary layer, while the aerosol extinction coefficient decreases with height. Generally, ozone and aerosol are negatively correlated below 650 m. The correlation coefficient increases with altitude and reaches a maximum of 0.379 at 1875 m. Within the boundary layer, ozone and aerosols are negatively correlated on days with particulate pollution (PM2.5 > 35 μg m−3), while on clean days they are positively correlated. Above the boundary layer, the correlation coefficient is usually positive, regardless of the presence of particulate pollution. The UAV study compensates for Lidar detections below 500 m. We found that ozone concentration is higher in the upper layers than in the near-surface layers, and that ozone depletion is faster in the near-surface layers after sunset. [ABSTRACT FROM AUTHOR]

Ozone (O3) is of great importance to air quality in the Yangtze River Delta (YRD) region, China. Focusing on surface O3 in the YRD, its spatiotemporal characteristics, meteorological driving factors, and health impacts are investigated based on surface O3 observations in this study. We find that from 2015 to 2019, most cities failed to meet the national standards and O3 pollution mainly occurred in warm seasons (April‐September). Surface O3 in the YRD increased in the recent years, so did tropospheric column O3. Spatially, surface shows a significant positive autocorrelation over the YRD except for 2019, and high O3 values mainly gather in the central of the YRD. The first two empirical orthogonal functions (EOFs) of O3 accounted for 37.4% and 20.0% of the total variance in O3, respectively, with their spatial patterns characterized by the same phase and west and east contrast, respectively. The EOF1 is related to the change in radiation and the EOF2 is attributed to regional transport by prevailing westerly wind. Downward UV radiation, temperature and u wind are crucial factors. The premature mortality caused by O3 for respiratory disease in the YRD is estimated to be 5,889 cases per year. Furthermore, we find that premature mortality is more sensitive to O3 concentration than population, suggesting that controlling peak O3 concentration can bring great health benefits. Key Points: Spatiotemporal characteristics of ozone were investigated based on satellite data and observation network dataThe main meteorological driving factors of ozone were captured using EOF analysisThe premature mortality attributed to ozone was estimated with epidemiological exposure response functions [ABSTRACT FROM AUTHOR]

Landfall typhoons can significantly affect O 3 in the Yangtze River Delta (YRD) region. In this study, we investigate a unique case characterized by two multiday regional O 3 pollution episodes related to four successive landfall typhoons in the summer of 2018 in the YRD. The results show that O 3 pollution episodes mainly occurred during the period from the end of a typhoon to the arrival of the next typhoon. The time when a typhoon reached the 24 h warning line and the time when the typhoon dies away in mainland China can be roughly regarded as time nodes. Meanwhile, the variations of O 3 were related to the track, duration and landing intensity of the typhoons. The impact of typhoons on O 3 was like a wave superimposed on the background of high O 3 concentration in the YRD in summer. When a typhoon was near the 24 h warning line before it landed on the coastline of the YRD, the prevailing wind originally from the ocean changed to be from inland, and it transported lots of precursors from the polluted areas to the YRD. Under influences of the typhoon, the low temperature, strong upward airflows, more precipitation and wild wind hindered occurrences of high O 3 episodes. After the passing of the typhoon, the air below the 700 hPa atmospheric layer was warm and dry, and the downward airflows resumed. The low troposphere was filed with high concentration of O 3 due to O 3 -rich air transported from the low stratosphere and strong photochemical reactions. It is noteworthy that O 3 was mainly generated in the middle of the boundary layer (∼ 1000 m) instead of at the surface. High O 3 levels remained in the residual layer at night, and would be transported to the surface by downward airflows or turbulence by the second day. Moreover, O 3 can be accumulated and trapped on the ground due to the poor diffusion conditions because the vertical diffusion and horizontal diffusion were suppressed by downward airflows and light wind, respectively. The premature deaths attributed to O 3 exposure in the YRD during the study period were 194.0, more than the casualties caused directly by the typhoons. This work has enhanced our understanding of how landfall typhoons affect O 3 in the YRD and thus can be useful in forecasting O 3 pollution in regions strongly influenced by typhoon activities. [ABSTRACT FROM AUTHOR]

Aerosols and ozone have significant influences on air qualities, human health, and climate changes. To further understand the characteristics and interactions among different urban air pollutants in the west Yangtze River Delta (YRD) region, continuous measurements of low-layer atmospheric particles and trace gases have been performed at an urban site in Nanjing from September 2016 to February 2017 in this study. In the urban area of the west YRD, the mean PM 10 and O3 concentrations are 86.3 µ g m -3 and 37.7 ppb, respectively, with significant seasonal and diurnal variations. Particles, which are dominated by fine aerosols, are relatively scattering. And most of their optical properties have similar variations to the aerosol concentrations. Results also show that the west YRD could still suffer severe air pollution, although the seasonal mean aerosol concentrations have decreased in recent years. Even in cold seasons, O3 could exceed the National Ambient Air Quality Standards for about 40 days during the sampling period. Most of polluted episodes are caused by local and subregional emissions. A case study for a typical O3 and PM 2.5 episode in December 2016 demonstrates that the episode was generally associated with regional transport and a stable weather system. Air pollutants were mostly transported from the western areas with high emissions, as well as with an anticyclone and high-pressure system in this region. Correlation analysis reveals that the interactions between O3 and PM are complex, with a combination of inhibition and promotion under different conditions. The inhibition effect might result from the reduction of photolysis frequency near the surface due to aerosols in addition to their positive correlations with precursors, while the promotion effect is from the formation of secondary aerosols under high concentrations of oxidants and solar radiation. However, the interaction between O3 and BC shows an inhibiting effect due to its chemical stability. This also indicated a VOC-sensitive regime for photochemical production of O3 in this region. This study further improves insight into the characteristics and interactions of main pollutants and may contribute to the improvement of the simulation and prediction of aerosols and gases in the urban area of the YRD. [ABSTRACT FROM AUTHOR]

Abstract: Agricultural fires could affect tropospheric photochemistry by emitting trace gases, interacting with solar radiation or providing reactive surfaces for heterogeneous reactions. This study examines the effects of a typical agricultural fire event (8–13 June 2012) on ozone photochemistry over the Yangtze River Delta region, East China. The online coupled Weather Research and Forecasting‐Chemistry model is used, with the inclusion of a detailed agricultural fire emission inventory and seven heterogeneous reactions on soot surfaces. Comparisons with satellite and ground observational data indicate that the model is capable of reproducing the transport and evolution of this crop fire event. The precursor emissions from agricultural fires play a major role in modifying ozone photochemistry, with a maximal increase in ozone mixing ratio reaching 20 ppb (40%) near the fire zones in northern Anhui. The radiation feedback generates a small increase of surface NO2 levels by 2% and a decrease in surface O3 levels by 1% in the smoke plume. The effects due to heterogeneous uptake on soot are rather small, on average, changing the average O3, NO2, ˙OH, and HO2˙ concentrations by +0.8%, −0.5%, −0.7%, and +0.8%, respectively. This study highlights the complicated interactions between agricultural fire emissions and photochemistry. [ABSTRACT FROM AUTHOR]

The natural emissions of ozone precursors (NO x and VOCs) are sensitive to climate. Future climate change can impact O 3 concentrations by perturbing these emissions. To better estimate the variation of natural emissions under different climate conditions and understand its effect on surface O 3 , we model the present and the future air quality over the Yangtze River Delta (YRD) region by running different simulations with the aid of the WRF-CALGRID model system that contains a natural emission module. Firstly, we estimate the natural emissions at present and in IPCC A1B scenario. The results show that biogenic VOC emission and soil NO x emission over YRD in 2008 is 657 Gg C and 19.1 Gg N, respectively. According to climate change, these emissions in 2050 will increase by 25.5% and 11.5%, respectively. Secondly, the effects of future natural emissions and meteorology on surface O 3 are investigated and compared. It is found that the variations in meteorological fields can significantly alter the spatial distribution of O 3 over YRD, with the increases of 5–15 ppb in the north and the decreases of −5 to −15 ppb in the south. However, only approximately 20% of the surface O 3 increases caused by climate change can be attributed to the natural emissions, with the highest increment up to 2.4 ppb. Finally, Ra (the ratio of impacts from NO x and VOCs on O 3 formation) and H 2 O 2 /HNO 3 (the ratio between the concentrations of H 2 O 2 and HNO 3 ) are applied to study the O 3 sensitivity in YRD. The results show that the transition value of H 2 O 2 /HNO 3 will turn from 0.3 to 0.5 in 2008 to 0.4–0.8 in 2050. O 3 formation in the YRD region will be insensitive to VOCs under future climate condition, implying more NO x need to be cut down. Our findings can help us understand O 3 variation trend and put forward the reasonable and effective pollution control policies in these famous polluted areas. [ABSTRACT FROM AUTHOR]

Ozone pollution is of great concern in the Yangtze River Delta (YRD) region of China. The regional air pollution is significantly associated with dominant weather systems. In this study, the relationship between O 3 concentration and weather patterns over the YRD region is investigated. Specifically, based on the National Center for Environmental Prediction reanalysis data and the sums-of-squares technique, six typical weather patterns in 2017 are identified. It is found that higher O 3 concentrations tend to occur under the weather patterns 3, 4 and 5. These high mean O 3 concentrations are associated with the southerly flow introduced by the western Pacific subtropical high, the low pressure in the saddle field and the warm ocean current introduced by typhoon. Whereas the low mean O 3 concentrations under the weather patterns 1, 2 and 6 are linked to the northwesterly flow brought from the Siberian high. Moreover, when the light pollution appears, main synoptic weather systems get weakened and the wind speed is reduced at 850 hPa and surface. At the same time, the temperature increases due to the weakening of the northerly wind introduced by the Siberian high and the North China warm high, and the strengthening of the southerly wind introduced by a southwest vortex. The occurrence of the heavy pollution is highly related to these further enhanced synoptic processes. The downward motion is obviously enhanced due to the trough or ridge deepening at 500 hPa and the strong downdraft around the typhoon. Higher temperature, lower wind and stronger downward motion due to the minor changes of atmospheric circulation establish conditions conducive to the formation and accumulation of O 3. • Weather patterns and their effects on different O 3 pollution levels in the YRD is investigated. • Six typical weather patterns are identified, and three pollution levels under them are further discussed. • O 3 pollution is related to the high-pressure systems, the southwest vortex, and the tropical cyclones. • Weakened northerly flow, low wind speed and strengthened downward motion are primarily factors to severe O 3 pollution. [ABSTRACT FROM AUTHOR]

Severe haze events and their radiation feedbacks exert a profound impact on the weather and tropospheric chemistry. Using the on-line-coupled Weather Research and Forecasting with Chemistry (WRF-Chem) model, this study investigates the impacts of direct aerosol-radiation feedbacks on local air quality (i.e. particulate matter and ozone photochemistry) during a severe autumn haze episode in Nanjing megacity, eastern China. Pronounced radiation feedbacks are found for the predictions of meteorological and chemical variables. In response to the negative radiative forcing of scattering-dominant anthropogenic haze aerosols, the instantaneous irradiance and temperature at the surface lower by 130 W m−2and 1.1–1.4 °C, respectively, leading to a reduction of boundary layer height by 103.2–232.6 m (11–38%) and vertical wind speed by 0.1–0.8 mm s−1(2–30% at mid-day) during this haze event. Such a stable atmosphere favours the accumulation of fine particles (30.5 μg m−3, 28.7%) and NO2(6.0 ppb, 23.7%) in the urban pollution plume. The weaker turbulent mixing and photochemical activity associated with the enhanced titration loss, and reduced downward radiation and photolysis rate result in a 0.1−5.0 ppb (12.0%) reduction of near-surface ozone. The simulations highlight that the aerosol-radiation feedbacks play an important role in the atmospheric transport and chemistry of large urban pollution plumes. [ABSTRACT FROM PUBLISHER]

Black carbon aerosol (BC) has significant impacts on regional climate changes due to its absorption of solar radiation, which might lead to substantial variations in surface ozone (O 3) pollution. Therefore, the potential role of the BC warming effect on O 3 responses during summertime in China is investigated and quantified based on online-coupled regional climate-chemistry model (RegCM-Chem) simulations and multiple linear regression (MLR) analysis. The results suggest that the absorption of solar radiation can lead to considerable decreases in cloud amount, precipitation and relative humidity in most regions of China in summer, which further cause a warming of the low-layer atmosphere and an enhancement in the southerly East Asian summer monsoon. The variations in O 3 concentrations in response to the BC warming effect are almost as large as the observed O 3 growth in China from 2013 to 2017 (7.2%). They have significant regional specificity over China. Due to the warming effect of BC, the near-surface daily O 3 concentrations are increased in most areas of Central to East China, with an increase of 6.2%, while they are decreased in Southwest China, with a reduction exceeding 5.8%, implying that BC emission reductions favor the mitigation of ozone pollution in East China in summer. Further investigations via MLR analysis indicate that the BC-induced O 3 increases in Central and East China and O 3 decreases in Southwest China are strongly related to changes in relative humidity, while the BC-induced O 3 increases in North and Northeast China are likely linked to the changes in transportation. These results may help us better understand the mechanism of O 3 variation and can provide a scientific reference for BC and O 3 reduction strategies over China. [Display omitted] • BC and surface O 3 is found to be significantly and positively correlated at over 80% sites of China. • BC warming effect has a contribution to surface O 3 growth in Eastern China (EC) in summer. • Humidity and transportation changed by BC are mostly responsible for O 3 increase in EC. [ABSTRACT FROM AUTHOR]

Ozone (O 3) and fine particulate matter (PM 2.5) are the major air pollutants, and CO 2 is a critical greenhouse gas in East Asia. They three are active species in terms of radiation. Most importantly, both O 3 and PM 2.5 can interact with CO 2 through the terrestrial ecosystem, thus having effects on the regional climate. This study investigated the mutual interactions among O 3 , PM 2.5 , and CO 2 on the East Asia summer monsoon climate using the coupling regional climate-chemistry-ecology model, RegCM-Chem-YIBs. Two numerical experiments were performed with and without involving the interactions among the three species. The investigations showed that the mutual interactions finally resulted in changes to surface PM 2.5 , O 3 , and CO 2 of -6∼-2 μg/m3, 4∼6 μg/m3, and 3∼5 ppm, respectively, in northern China. While in southern China, surface PM 2.5 , O 3 , and CO 2 varied in the range of 2∼4 μg/m3, 1∼2 μg/m3, and -4∼-2 ppm. Surface downward shortwave radiation flux (SWF) and longwave radiation flux (LWF) increased in northern China, whereas showed decreasing in southern China. The lower atmosphere was warmed by 1∼2 K in north China, enlarging the air temperature gradient between land and sea, inducing easterly and southerly winds at 850 hpa in the region. On the contrary, surface cooling (-2∼-1K) exhibited northerly wind anomalies in southern China. The results indicated that the mutual interactions among the three species could significantly impact regional climate. We argue that future simulations should consider these interactions to better predict air pollution and climate changes in the target region. This work could help to comprehensively understand the climate effects of the mutual interactions among O 3 , PM 2.5 , and CO 2. The findings provide a scientific reference for the collaborative governance of regional climate and air pollution in East Asia. • Mutual interactions among O 3 , PM 2.5 , and CO 2 are considered in RegCM-Chem-YIBs. • More realistic simulations on meteorolgy and air pollution in East Asia were found when mutual interactions were involved. • The mutual interactions can significantly modify the summer monsoon climate in East Asia. [ABSTRACT FROM AUTHOR]

Dust aerosols could affect tropospheric photochemistry by interacting with solar radiation or providing reactive surfaces for heterogeneous reactions. This study examines the effects of a typical springtime dust storm (16–18 March, 2014) on ozone photochemistry over the downstream Nanjing megacity in eastern China. The on-line coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model is used, with the inclusion of eight heterogeneous reactions on dust surfaces. Comparisons with satellite data and visibility record indicate that the model is capable of reproducing the onset time and downstream transport of this dust event. Dust particles act as a sink for all these trace gases examined here. The net decreases of O 3 , NO 2 , NO 3 , N 2 O 5 , HNO 3 , OH, HO 2 and H 2 O 2 in the atmosphere are estimated as −6.1%, −16.0%, −37.4%, −13.9%, −47.7%, −6.0%, −9.2% and −29.7%, of which more than 80% can be explained by heterogeneous chemistry on dust surfaces. The decreases in ground photolysis rate and OH concentration, along with changes in other weather variables induced by dust aerosols (i.e., radiation and temperature) lead to lower photochemical activity and a small decrease of O 3 mixing ratio by roughly 0.5%. This study highlights the importance of dust interaction with ozone photochemistry, and also sets the stage for further investigation of the complicated dust impacts on tropospheric aerosol chemistry. [ABSTRACT FROM AUTHOR]

A continuous and heavy photochemical pollution episode when Typhoon Nari occurred during Sep. 14–19, 2001 in Hong Kong was studied by use of the new generation of regional air quality model WRF–chem V2.1, in which the meteorological model (WRF) and chemical model (chem) are fully coupled on line. In this episode, the regional air quality monitoring stations in Hong Kong recorded high concentrations of O3, CO and NO x for six days, the maximum concentration of O3 reached 191ppb, and the atmospheric visibility dropped to 1.8km. Investigations showed that WRF–chem can basically simulate this continuous photochemical pollution episode, with the best correlation coefficient of the simulated and the observed O3 concentrations being 0.84. The production and loss of O3 were significant in this episode, and the largest rates were 22.7 and −17.6ppbh−1, respectively. The simulated meteorological conditions showed high temperature, lower relative humidity, strong solar radiation, northerly airstream, and stable boundary layer structure in Hong Kong during the episode, these weather factors were conducive to formation and maintenance of photochemical pollution. It was also clear that the vertical transport played an important role in this episode. As controlled by downdraft at the outside of Typhoon system with more stable atmosphere, air pollutants were limited and accumulated in the low level of boundary layer, leading to high O3 concentration from photochemical formation. [Copyright &y& Elsevier]

With the enactment of Air Pollution Action Plan in 2013, the air quality improved in most Chinese cities, except that surface ozone (O 3) increased markedly. Some recent studies have examined this issue and presented controversial opinions, but only focus on summertime ozone increase. This study extends a comprehensive analysis of the influencing factors on China's ozone changes from 2013 to 2017 out of the summer season, combining satellite data, ground measurements and model analyses. The annual trends of air pollutants, e.g., increase in 95th percentile O 3 concentration (+1.4–8.7 μg m−3 yr−1), and decreases in fine particulate matter (PM 2.5 ; −4.0~−7.5 μg m−3 yr−1) and sulfur dioxide (−2.6~−9.7 μg m−3 yr−1) are uncovered by satellite and observational data. Model results show that the attributions of surface O 3 changes from 2013 to 2017 vary spatially and seasonally, and most regions are more affected by emission changes (−9.5–47.0 μg m−3) rather than meteorological changes (−8.1–21.3 μg m−3). In specific regions and seasons, e.g., south/southwestern and eastern China south of 35°N in May and July, the surface O 3 responses to climate variability could have an equal or even greater importance than emission changes. In these major pollution control regions, e.g. northern and mid-eastern China, the precursor emissions control (11–35%) contributes in the same degree as the changes in aerosol effects (35–38%) to surface ozone enhancement in the warm seasons. More scientific emission controls and climate adaptation strategies are required to attain the synergetic control of atmospheric particulate matter and ozone in China. Image 1 • Air pollution trends are uncovered by satellite data and observations. • The attributions of surface O 3 changes are more affected by emission changes. • O 3 response to atmospheric warming is dominant south of 30°N in warm season. • NO x and VOC s control contributed equally as aerosol effect in NCP and East China. [ABSTRACT FROM AUTHOR]

The vertical structure of ozone (O 3) and fine particulate matter (FPM) as well as their interactions are important for understanding the atmospheric chemistry process and their impact on climate. Through a ground-based lidar observation during April 18th-May 22nd 2017 and surface measurement during March 1st-May 31st 2017, this study obtained the vertical distribution of O 3 and aerosol extinction coefficient with their correlations during the springtime in the lower troposphere (LT) in Nanjing, eastern China. Surface average O 3 and PM 2.5 concentrations in spring were 39.89 ppb and 41.93 μg m−3. O 3 generally increased with height in the LT, while aerosol extinction coefficient decreased. The correlation between O 3 and aerosol extinction coefficient was −0.32 at 300 m, and 0.34 at 1747.5 m. An on-line coupled model Weather Research and Forecasting with Chemistry (WRF-Chem) was used to analyze the effect of aerosol's radiation feedback on ozone. Aerosol reduced the surface downward shortwave radiation by −25.66 W m−2, and increased the upwelling shortwave radiation at the top of atmosphere by 3.19 W m−2 in urban Nanjing. The photolysis rate of NO 2 and O1D were reduced by −1% and −0.7% near surface and increased by 0.3% and 0.2% at upper LT. Aerosol-included effect also led to a more stable planet boundary layer (PBL), with −0.24 °C and −0.05 m s−1 changes in temperature and wind speed at surface. However, the temperature and wind speed increased by 0.18 °C and 0.13 m s−1 at 1760 m, respectively. O 3 decreased by −3.70% at surface and increased by 0.89% at 2870 m. This study showed that aerosol can affect ozone through altering photolysis rate and atmospheric stability. Aerosol's radiation feedback has a complex effect on the vertical structure of ozone, which leads to ozone decrease near the surface and increase above the aerosol layer. • The vertical structure and the correlation of O 3 and PM 2.5 were analyzed. • O 3 increases with height in the lower troposphere, while aerosol decreases. • PM 2.5 reduces surface O 3 by reducing photolysis rate and increasing PBL stability. • PM 2.5 and O 3 are positive correlated at higher altitudes. [ABSTRACT FROM AUTHOR]