scholarly journals Air quality and health benefits from ultra-low emission control policy indicated by continuous emission monitoring: a case study in the Yangtze River Delta region, China

2021 ◽  
Vol 21 (8) ◽  
pp. 6411-6430
Author(s):  
Yan Zhang ◽  
Yu Zhao ◽  
Meng Gao ◽  
Xin Bo ◽  
Chris P. Nielsen
Keyword(s):  
Air Quality ◽  
Power Plants ◽  
Yangtze River Delta ◽  
Base Case ◽  
Continuous Emission ◽  
Power Sector ◽  
Low Emission ◽  
The Yrd ◽  
The Yangtze River Delta ◽  
Emission Policy

Abstract. To evaluate the improved emission estimates from online monitoring, we applied the Models-3/CMAQ (Community Multiscale Air Quality) system to simulate the air quality of the Yangtze River Delta (YRD) region using two emission inventories with and without incorporated data from continuous emission monitoring systems (CEMSs) at coal-fired power plants (cases 1 and 2, respectively). The normalized mean biases (NMBs) between the observed and simulated hourly concentrations of SO2, NO2, O3, and PM2.5 in case 2 were −3.1 %, 56.3 %, −19.5 %, and −1.4 %, all smaller in absolute value than those in case 1 at 8.2 %, 68.9 %, −24.6 %, and 7.6 %, respectively. The results indicate that incorporation of CEMS data in the emission inventory reduced the biases between simulation and observation and could better reflect the actual sources of regional air pollution. Based on the CEMS data, the air quality changes and corresponding health impacts were quantified for different implementation levels of China's recent “ultra-low” emission policy. If the coal-fired power sector met the requirement alone (case 3), the differences in the simulated monthly SO2, NO2, O3, and PM2.5 concentrations compared to those of case 2, our base case for policy comparisons, would be less than 7 % for all pollutants. The result implies a minor benefit of ultra-low emission control if implemented in the power sector alone, which is attributed to its limited contribution to the total emissions in the YRD after years of pollution control (11 %, 7 %, and 2 % of SO2, NOX, and primary particle matter (PM) in case 2, respectively). If the ultra-low emission policy was enacted at both power plants and selected industrial sources including boilers, cement, and iron and steel factories (case 4), the simulated SO2, NO2, and PM2.5 concentrations compared to the base case would be 33 %–64 %, 16 %–23 %, and 6 %–22 % lower, respectively, depending on the month (January, April, July, and October 2015). Combining CMAQ and the Integrated Exposure Response (IER) model, we further estimated that 305 deaths and 8744 years of life loss (YLL) attributable to PM2.5 exposure could be avoided with the implementation of the ultra-low emission policy in the power sector in the YRD region. The analogous values would be much higher, at 10 651 deaths and 316 562 YLL avoided, if both power and industrial sectors met the ultra-low emission limits. In order to improve regional air quality and to reduce human health risk effectively, coordinated control of multiple sources should be implemented, and the ultra-low emission policy should be substantially expanded to major emission sources in industries other than the power industry.

scholarly journals Air quality and health benefits from ultra-low emission control policy indicated by continuous emission monitoring: A case study in the Yangtze River Delta region, China

2020 ◽  
Author(s):  
Yan Zhang ◽  
Yu Zhao ◽  
Meng Gao ◽  
Xin Bo ◽  
Chris P. Nielsen
Keyword(s):  
Air Quality ◽  
Emission Control ◽  
Control Policy ◽  
Yangtze River Delta ◽  
Base Case ◽  
Power Sector ◽  
Low Emission ◽  
Industrial Boilers ◽  
The Yrd ◽  
Emission Policy

Abstract. To evaluate improved emission estimation from online monitoring data, we applied the Models-3/CMAQ (Community Multi-scale Air Quality) system to simulate the air quality of the Yangtze River Delta (YRD) region using two emission inventories without/with incorporated data from continuous emission monitoring systems (CEMS) at coal-fired power plants (Cases 1 and 2), respectively. The normalized mean biases (NMBs) of annual SO2, NO2, O3 and PM2.5 concentrations between observations and simulations in Case 2 were −3.1 %, 56.3 %, −19.5 % and −1.4 %, all smaller in absolute value than those in Case 1, at 8.2 %, 68.9 %, −24.6 % and 7.6 %, respectively. The results indicate that incorporation of CEMS data in the emission inventory helped reduce the biases between simulation and observation and can better reflect the actual sources of regional air pollution. Based on the CEMS data, the air quality changes and corresponding health impacts were quantified for different implementation levels of China's recent ultra-low emission policy. If only the coal-fired power sector met the requirement, the simulated differences in the monthly SO2, NO2, O3 and PM2.5 concentrations compared to those of Case 2, our base case for policy comparisons, were less than 7 % for all pollutants. The result implies only a minor benefit of ultra-low emission control if implemented in the power sector alone, attributed to its limited contribution to total emissions in the YRD after years of pollution control in the sector (11 %, 7 % and 2 % of SO2, NOX and primary particle matter (PM), respectively). If the ultra-low emission policy was enacted at both power plant and industrial boilers, the simulated SO2, NO2 and PM2.5 concentrations compared to the base case were 33 %–64 %, 16 %–23 % and 6 %–22 % lower respectively, depending on the month (January, April, July and October 2015). Combining CMAQ and the Integrated Exposure Response (IER) model, we further estimated that 305 deaths and 874 years of life loss (YLL) attributable to PM2.5 exposure could be avoided with the implementation of the ultra-low emission policy in the power sector in the YRD region. The analogous values would be much higher, at 10,651 deaths and 316,562 YLL avoided, if both power and industrial sectors met the ultra-low emission limits, accounting for 5.5 % and 6.2 % of the totals for the region, respectively. In order to improve regional air quality and to reduce human health risk effectively, coordinated control of various pollution sources should be implemented, and the ultra-low emission control policy should be substantially expanded to industrial boilers and other emission sources in non-power industries.

scholarly journals Modeling of the anthropogenic heat flux and its effect on regional meteorology and air quality over the Yangtze River Delta region, China

2016 ◽  
Vol 16 (10) ◽  
pp. 6071-6089 ◽  
Author(s):  
Min Xie ◽  
Jingbiao Liao ◽  
Tijian Wang ◽  
Kuanguang Zhu ◽  
Bingliang Zhuang ◽  
...  
Keyword(s):  
Air Quality ◽  
Urban Areas ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
Vertical Movement ◽  
Anthropogenic Heat ◽  
The Yangtze River ◽  
The Yrd ◽  
Surface O3 ◽  
The Yangtze River Delta

Abstract. Anthropogenic heat (AH) emissions from human activities caused by urbanization can affect the city environment. Based on the energy consumption and the gridded demographic data, the spatial distribution of AH emission over the Yangtze River Delta (YRD) region is estimated. Meanwhile, a new method for the AH parameterization is developed in the WRF/Chem model, which incorporates the gridded AH emission data with the seasonal and diurnal variations into the simulations. By running this upgraded WRF/Chem for 2 typical months in 2010, the impacts of AH on the meteorology and air quality over the YRD region are studied. The results show that the AH fluxes over the YRD have been growing in recent decades. In 2010, the annual-mean values of AH over Shanghai, Jiangsu and Zhejiang are 14.46, 2.61 and 1.63 W m−2, respectively, with the high value of 113.5 W m−2 occurring in the urban areas of Shanghai. These AH emissions can significantly change the urban heat island and urban-breeze circulations in the cities of the YRD region. In Shanghai, 2 m air temperature increases by 1.6 °C in January and 1.4 °C in July, the PBLH (planetary boundary layer height) rises up by 140 m in January and 160 m in July, and 10 m wind speed is enhanced by 0.7 m s−1 in January and 0.5 m s−1 in July, with a higher increment at night. The enhanced vertical movement can transport more moisture to higher levels, which causes the decrease in water vapor at ground level and the increase in the upper PBL (planetary boundary layer), and thereby induces the accumulative precipitation to increase by 15–30 % over the megacities in July. The adding of AH can impact the spatial and vertical distributions of the simulated pollutants as well. The concentrations of primary air pollutants decrease near the surface and increase at the upper levels, due mainly to the increases in PBLH, surface wind speed and upward air vertical movement. But surface O3 concentrations increase in the urban areas, with maximum changes of 2.5 ppb in January and 4 ppb in July. Chemical direct (the rising up of air temperature directly accelerates surface O3 formation) and indirect (the decrease in NOx at the ground results in the increase in surface O3) effects can play a significant role in O3 changes over this region. The meteorology and air pollution predictions in and around large urban areas are highly sensitive to the anthropogenic heat inputs, suggesting that AH should be considered in the climate and air quality assessments.

scholarly journals Source, transport and impacts of a heavy dust event in the Yangtze River Delta, China in 2011

2013 ◽  
Vol 13 (8) ◽  
pp. 21507-21540
Author(s):  
X. Fu ◽  
S. X. Wang ◽  
Z. Cheng ◽  
J. Xing ◽  
B. Zhao ◽  
...  
Keyword(s):  
Air Quality ◽  
Yangtze River ◽  
Eastern China ◽  
Yangtze River Delta ◽  
River Delta ◽  
Dust Particles ◽  
The Yangtze River ◽  
Dust Event ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. During 1 to 6 May 2011, a dust event was observed in the Yangtze River Delta region (YRD). The highest PM10 concentration reached over 1000 μg m−3 and the visibility was below 3 km. In this study, the Community Multi-scale Air Quality modeling system (CMAQ5.0) coupled with an in-line windblown dust model was used to simulate the formation, spatial and temporal characteristics of this dust event, and analyze its impacts on deposition and photochemistry. The threshold friction velocity for loose smooth surface in the dust model was revised based on Chinese data to improve the model performance. The comparison between predictions and observations indicates the revised model can reproduce the transport and pollution of the event. The simulation results show that the dust event was affected by formation and transport of Mongolian cyclone and cold air. Totally about 695 kt dust particles (PM10) were emitted in Xinjiang Province and Mongolia during 28 to 30 April, the dust band swept northern, eastern China and then arrived in the YRD region on 1 May 2011. The transported dust particles increased the mean surface layer concentrations of PM10 in the YRD region by 372% during 1 to 6 May and the impacts weakened from north to south due to the removal of dust particles along the path. Accompanied by high PM concentration, the dry deposition, wet deposition and total deposition of PM10 in the YRD reached 184.7 kt, 172.6 kt and 357.32 kt, respectively. These deposited particles are very harmful because of their impacts on urban environment as well as air quality and human health when resuspending in the atmosphere. Due to the impacts of mineral dust on atmospheric photolysis, the concentrations of O3 and OH were reduced by 1.5% and 3.1% in the whole China, and by 9.4% and 12.1% in the YRD region, respectively. The work of this manuscript is meaningful for understanding the dust emissions in China as well as for the application of CMAQ in Asia. It is also helpful to understand the formation mechanism and impacts of dust pollution in the YRD.

scholarly journals Enhanced sulfate formation through SO<sub>2</sub>+NO<sub>2</sub> heterogeneous reactions during heavy winter haze in the Yangtze River Delta region, China

2019 ◽  
Author(s):  
Ling Huang ◽  
Jingyu An ◽  
Bonyoung Koo ◽  
Greg Yarwood ◽  
Rusha Yan ◽  
...  
Keyword(s):  
Air Quality ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
Heterogeneous Reactions ◽  
Ammonia Emissions ◽  
The Yangtze River ◽  
Uptake Mechanism ◽  
Sulfate Formation ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Rapid sulfate formation is recognized as key characteristics of severe winter haze in China. However, air quality models tend to underestimate sulfate formation during heavy haze periods and heterogeneous formation pathways have been proposed as promising mechanisms to reduce gaps between observation and model simulation. In this study, we implemented a reactive SO2 uptake mechanism through the SO2+NO2 heterogeneous reactions in the Comprehensive Air Quality Model with extensions (CAMx) to improve simulation of sulfate formation in the Yangtze River Delta (YRD) region for the first time. Parameterization of the SO2+NO2 heterogeneous reactions is based on observations in Beijing and considered both impact of relative humidity and aerosol pH on sulfate formation. Ammonia is reported to be critical for the formation of secondary inorganic aerosols and estimation of ammonia emissions is usually associated with large uncertainties. Sensitivity tests were conducted to evaluate the importance of the SO2+NO2 heterogeneous reactions as well as ammonia emissions on modelled sulfate concentrations during a period with several heavy haze episodes in the YRD region. Base case model results show large underestimation of sulfate concentrations by 36 % under polluted conditions in the YRD region. Adding the SO2+NO2 heterogeneous reactions or doubling ammonia emissions alone leads to slight model improvement (~ 6 %) on simulated sulfate concentrations in the YRD region. However, model performance significantly improved when both the SO2+NO2 heterogeneous reactions and doubled ammonia emissions were included in the simulation: predicted sulfate concentrations during polluted periods increased from 23.1 µg m−3 in the base scenario to 29.1 µg m−3 (representing an increase of 26 %). Aerosol pH is crucial for the SO2+NO2 heterogeneous reactions and our calculated aerosol pH is always acidic and increased by 0.7 with doubled ammonia emissions. Modelling results also show that this reactive SO2 uptake mechanism enhanced sulfate simulations by 1 to 5 µg m−3 for the majority of eastern and central part of China, with more than 20 µg m−3 increase of sulfate concentrations over the north-eastern plateau. These findings suggest that the SO2+NO2 heterogeneous reactions could be important for sulfate formation in the YRD region as well as other parts of China. In addition, ammonia emissions need to be carefully estimated. More studies are needed to improve the parameterization of the SO2+NO2 heterogeneous reactions based on local data further evaluate this mechanism in other regions. Substantial efforts are needed to improve the accuracy of ammonia emissions inventory.

scholarly journals The influence of spatiality on shipping emissions, air quality and potential human exposure in the Yangtze River Delta/Shanghai, China

2019 ◽  
Vol 19 (9) ◽  
pp. 6167-6183 ◽  
Author(s):  
Junlan Feng ◽  
Yan Zhang ◽  
Shanshan Li ◽  
Jingbo Mao ◽  
Allison P. Patton ◽  
...  
Keyword(s):  
Air Quality ◽  
Yangtze River ◽  
Human Exposure ◽  
Yangtze River Delta ◽  
River Delta ◽  
The Yangtze River ◽  
Inland Water ◽  
The Yrd ◽  
The Impact ◽  
The Yangtze River Delta

Abstract. The Yangtze River Delta (YRD) and the megacity of Shanghai are host to one of the busiest port clusters in the world; the region also suffers from high levels of air pollution. The goal of this study was to estimate the contributions of shipping to regional emissions, air quality, and population exposure and to characterize the importance of the geographic spatiality of shipping lanes and different types of ship-related sources for the baseline year of 2015, which was prior to the implementation of China's Domestic Emission Control Areas (DECAs) in 2016. The WRF-CMAQ model, which combines the Weather Research and Forecasting model (WRF) and the Community Multi-scale Air Quality (CMAQ) model, was used to simulate the influence of coastal and inland-water shipping, port emissions and ship-related cargo transport on air quality and on the population-weighted concentrations (which is a measure of human exposure). Our results showed that the impact of shipping on air quality in the YRD was primarily attributable to shipping emissions within 12 NM (nautical miles) of shore, but emissions coming from the coastal area between 24 and 96 NM still contributed substantially to ship-related PM2.5 concentrations in the YRD. The overall contribution of ships to the PM2.5 concentration in the YRD could reach 4.62 µg m−3 in summer when monsoon winds transport shipping emissions onshore. In Shanghai city, inland-water going ships were major contributors (40 %–80 %) to the shipping impact on urban air quality. Given the proximity of inland-water ships to the urban populations of Shanghai, the emissions of inland-water ships contributed more to population-weighted concentrations. These research results provide scientific evidence to inform policies for controlling future shipping emissions; in particular, in the YRD region, expanding the boundary of 12 NM from shore in China's current DECA policy to around 100 NM from shore would include most of shipping emissions affecting air pollutant exposure, and stricter fuel standards could be considered for the ships on inland rivers and other waterways close to residential regions.

scholarly journals An important mechanism of regional O<sub>3</sub> transport for summer smog over the Yangtze River Delta in East China

2018 ◽  
Author(s):  
Jun Hu ◽  
Yichen Li ◽  
Tianliang Zhao ◽  
Jane Liu ◽  
Xiao-Ming Hu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
The Yangtze River ◽  
Easterly Wind ◽  
Summer Smog ◽  
The Yrd ◽  
Surface O3 ◽  
The Yangtze River Delta

Abstract. Severe ozone (O3) pollution episodes plague a few regions in Eastern China at times, e.g., the Yangtze River Delta (YRD). The formation mechanisms including contributing meteorological factors of these severe pollution events remain elusive. A severe summer smog stretched over the YRD region from August 22 to 25, 2016 with hourly surface O3 concentrations exceeding 300 µg m−3 on August 25 in Nanjing, located in the western YRD. The weather pattern of this episode was characterized by near-surface prevailing easterly wind and continuous high air temperature. The formation mechanism of this O3 episode over the YRD area, particularly the extreme values over western YRD, was investigated using observation data and simulation with the Weather Research and Forecasting model with Chemistry (WRF-Chem). The O3 pollution episode was generally well simulated by the WRF-Chem air quality model. On August 24, the high O3 levels with the peak values of 250 µg m−3 occurred in the daytime mixing layer over the eastern YRD area. During nighttime, a shallow stable boundary layer formed near the surface, which decoupled the residual layer (RL) above it from the surface. O3 in the decoupled RL remained nearly constant, resulting an O3-rich reservoir, due to lack of NO titration and absence of dry deposition. The prevailing easterly wind in the lower troposphere transported the O3-rich air mass in the nocturnal RL from the eastern to western YRD. Consequently, the O3 concentrations in the RL over the western YRD area increased to 170 µg m−3 in the wee hours of August 25, 2016. Due to the growth of the convective boundary layer after the sunrise, entrainment of O3-rich RL air and boundary layer mixing contributed considerably to the rapid increase of surface O3. Process analysis indicated vertical mixing contributed ~ 40 µg m−3 h−1 of O3 accumulation over Nanjing in the morning of August 25, 2016, which played an important role in contributing to the severe daytime O3 pollution in the western YRD area. The mechanism of regional O3 transport through the nocturnal RL has a great implication for understanding O3 pollution in air quality change.

scholarly journals Air quality and emissions in the Yangtze River Delta, China

2010 ◽  
Vol 10 (10) ◽  
pp. 23657-23703
Author(s):  
L. Li ◽  
C. H. Chen ◽  
C. Huang ◽  
Y. J. Wang ◽  
H. Y. Huang ◽  
...  
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
River Delta ◽  
Pollution Monitoring ◽  
The Yangtze River ◽  
Monthly Average ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Regional trans-boundary air pollution has become an important issue in the field of air pollution modeling. This paper presents the results of the implementation of the MM5-CMAQ modeling system in the Yangtze River Delta (YRD) for the months of January and July of 2004. The meteorological parameters are obtained by using the MM5 model. A new regional emission inventory with spatial and temporal allocations based on local statistical data has been developed to provide input emissions data to the MM5-CMAQ modeling system. The pollutant concentrations obtained from the MM5-CMAQ modeling system have been compared with observational data from the national air pollution monitoring network. It is found that air quality in winter in the YRD is generally worse than in summer, due mainly to unfavorable meteorological dispersion conditions. In winter the pollution transport from Northern China to the YRD reinforces the pollution caused by large local emissions. The monthly average concentration of SO2 in the YRD is 0.026 ± 0.011 mg m−3 in January and 0.017 ± 0.009 mg m−3 in July. Monthly average concentrations of NO2 in the YRD in January and July are 0.021 ± 0.009 mg m−3, and 0.014 ± 0.008 mg m−3 respectively. Visibility is also a problem, with average deciview values of 26.4 ± 2.95 dcv in winter and 17.6 ± 3.3 dcv in summer. The ozone concentration in the downtown area of a city like Zhoushan can be very high, with the highest simulated value reaching 107 ppb. Our results show that ozone and haze have become extremely important issues in the regional air quality. Thus, regional air pollution control is urgently needed to improve air quality in the YRD.

scholarly journals Changes in source contributions of particulate matter during COVID-19 pandemic in the Yangtze River Delta, China

2021 ◽  
Author(s):  
Jinlong Ma ◽  
Juanyong Shen ◽  
Peng Wang ◽  
Shengqiang Zhu ◽  
Yu Wang ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Yangtze River ◽  
Organic Aerosol ◽  
Yangtze River Delta ◽  
The Yangtze River ◽  
Emission Reductions ◽  
Source Contributions ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Within a short time after the outbreak of coronavirus disease 2019 (COVID-19) in Wuhan, Hubei, the Chinese government took a nationwide lockdown to prevent the spread of the pandemic. The quarantine measures have significantly decreased the anthropogenic activities, and thus improving the air quality. To study the impacts caused by the lockdown on specific source sectors and regions in the Yangtze River Delta (YRD), the Community Multiscale Air Quality (CMAQ) model was used to investigate the changes in source contributions to fine particulate matter (PM2.5) from January 23 to February 28, 2020, based on different emission control cases. Compared to Case 1 (without emission reductions), the total PM2.5 mass for Case 2 (with emission reductions) decreased by larger than 20 % over the entire YRD and the reduction ratios of its components were 15 %, 16 %, 20 %, 43 %, 34 %, and 35 % in primary organic aerosol (POA), elemental carbon (EC), sulfate, nitrate, ammonium, and secondary organic aerosol (SOA), respectively. The source appointment results showed that PM2.5 concentrations from transportation decreased by 40 % while from residential and power decreased by less than 10 % due to the lockdown. Although all sources decreased, the relative contribution changed differently. Contributions of residential increased by more than 10 % to 35 %, while that of the industry decreased to 33 %. Considering the regional transport, the total PM2.5 mass of all regions decreased 20–30 % in the YRD with the largest decreased value of 5.0 μg m−3 in Henan, Hebei, Beijing, and Tianjin (Ha-BTH). In Shanghai, the lower contributions from local emissions and regional transmission (mainly Shandong and Ha-BTH) led to the reduced PM2.5. This study suggested adjustments of control measures for various sources and regions. Also, it was necessary to strengthen the regional collaboration at a large scale to improve the air quality in the YRD.

scholarly journals Integrated studies of a regional ozone pollution synthetically affected by subtropical high and typhoon system in the Yangtze River Delta region, China

2016 ◽  
Vol 16 (24) ◽  
pp. 15801-15819 ◽  
Author(s):  
Lei Shu ◽  
Min Xie ◽  
Tijian Wang ◽  
Da Gao ◽  
Pulong Chen ◽  
...  
Keyword(s):  
Air Quality ◽  
Yangtze River ◽  
Western Pacific Subtropical High ◽  
Yangtze River Delta ◽  
Western Pacific ◽  
Subtropical High ◽  
The Yangtze River ◽  
The Yrd ◽  
The Yangtze River Delta ◽  
The Western Pacific

Abstract. Severe high ozone (O3) episodes usually have close relations to synoptic systems. A regional continuous O3 pollution episode was detected over the Yangtze River Delta (YRD) region in China during 7–12 August 2013, in which the O3 concentrations in more than half of the cities exceeded the national air quality standard. The maximum hourly concentration of O3 reached 167.1 ppb. By means of the observational analysis and the numerical simulation, the characteristics and the essential impact factors of the typical regional O3 pollution are comprehensively investigated. The observational analysis shows that the atmospheric subsidence dominated by the western Pacific subtropical high plays a crucial role in the formation of high-level O3. The favorable weather conditions, such as extremely high temperature, low relative humidity and weak wind speed, caused by the abnormally strong subtropical high are responsible for the trapping and the chemical production of O3 in the boundary layer. In addition, when the YRD cities are at the front of Typhoon Utor, the periphery circulation of typhoon system can enhance the downward airflows and cause worse air quality. However, when the typhoon system weakens the subtropical high, the prevailing southeasterly surface wind leads to the mitigation of the O3 pollution. The integrated process rate (IPR) analysis incorporated in the Community Multi-scale Air Quality (CMAQ) model is applied to further illustrate the combined influence of subtropical high and typhoon system in this O3 episode. The results show that the vertical diffusion (VDIF) and the gas-phase chemistry (CHEM) are two major contributors to O3 formation. During the episode, the contributions of VDIF and CHEM to O3 maintain the high values over the YRD region. On 10–12 August, the cities close to the sea are apparently affected by the typhoon system, with the contribution of VDIF increasing to 28.45 ppb h−1 in Shanghai and 19.76 ppb h−1 in Hangzhou. In contrast, the cities far away from the sea can hardly be affected by the periphery circulation of typhoon system. When the typhoon system significantly weakens the subtropical high, the contribution values of all individual processes decrease to a low level in all YRD cities. These results provide an insight for the O3 pollution synthetically impacted by the western Pacific subtropical high and the tropical cyclone system.

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