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The adverse health effects of PM 2.5 have been well demonstrated by many studies. However, as a component of PM 2.5 , evidence on the mortality risk of black carbon (BC) is still limited. In this study, based on the data of daily mean PM 2.5 concentration, BC concentration, meteorological factors, total non-accidental (all-cause) and cardiovascular mortality in Shanghai and Nanjing during 2015-2016, a semi-parameter generalized additive model (GAM) in the time series and the constituent residual approach were employed to explore the exposure-response relationship between BC and human mortality in these two megacities of Yangtze River Delta, China. The main objective was to separate the health effects of BC from total PM 2.5 , and compare the difference of mortality ER related to BC original concentration and adjusted concentration after controlling PM 2.5 . Results showed that there were all significantly associated with daily mortality for PM 2.5 and BC. The percentage excess risk (ER) increases in all-cause and cardiovascular categories were 1.68 % (95 % s 1.28, 2.08) and 2.16 % (95 % CI: 1.54, 2.79) with 1 μg/m 3 increment in original BC concentration in Shanghai. And the ER in Nanjing was smaller than that in Shanghai. After eliminating PM 2.5 confounding effects by a constituent residual approach, the BC residual concentration still had a strong significant ER. The ER for BC residual in Shanghai got an obvious increase, and ER of the cardiovascular mortality for all, females and males increased by 0.55 %, 1.46 % and 0.62 %, respectively, while the ER in Nanjing decreased slightly. It also revealed that females were more sensitive to the health risk associated with short-term BC exposure than males. Our findings provide additional important evidence and ER for mortality related to independent BC exposure. Therefore, BC emission reduction should be paid more attention in air pollution control strategies to reduce BC-related health burdens., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in or the review of the manuscript entitled., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A multiscale analysis of meteorological trends was carried out to investigate the impacts of the large-scale circulation types as well as the local-scale key weather elements on the complex air pollutants, i.e., PM 2.5 and O 3 in China. Following accompanying papers on synoptic circulation impact and key weather elements and emission contributions (Gong et al., 2022a; Gong et al., 2022b), an emission-driven Observation-based Box Model (e-OBM) was developed to study the impact mechanisms on O 3 trend and quantitatively assess the effects of variation in the emissions control over 2013-2020 for Beijing, Chengdu, Guangzhou and Shanghai. Compared with the original OBM, the e-OBM not only improves the performance to simulate the hourly O 3 peak concentration in daytime, but also reasonably reproduces the maximum daily 8-hour average (MDA8) O 3 concentrations in the four cities. Based upon the sensitivity experiments, it is found that the meteorology is the dominant driver for the MDA8 O 3 trend, contributing from about 32 % to 139 % to the variations. From the mechanistic point of view, the variations of meteorology lead to the enhancement of atmospheric oxidation capacity and the acceleration of O 3 production. Further evaluation to the emission changes in four cities shows that the O 3 -precursors relationships of the four cities have been changed from the VOC-limited regime in 2013 to the transition regime or near-transition regime in 2020. Though the NO x /VOCs ratios have been obviously decreased, the emission reductions up to 2020 were still not enough to mitigate O 3 pollution in these cities. It is emphasized in this study that the strengthened control measures with maintaining a certain ratio of NO x and VOCs should be implemented to further curb the increasing trend of O 3 in urban areas., 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 B.V. All rights reserved.)

The Sichuan Basin (SCB) of China is known for excessive ozone (O 3 ) pollution owing to high anthropogenic emissions combined with terrain-induced poor ventilation and weak wind fields against the surrounding mountains. While O 3 pollution has emerged as a prominent concern in southwestern China yet variations in O 3 levels during 2013-2020 are still unclear and the dominant factor in explaining the long-term O 3 trend throughout the SCB remains elusive due to uncertainties in emission inventory and variability associated with meteorological conditions. Here, we use extensive basin-wide ambient measurements to examine the spatial pattern and trend of O 3 and leverage OMI and TROPOMI satellites in conjunction with MEIC emission inventory to track emission changes. Sensitivity simulations are conducted by using WRF-CMAQ model to investigate the impacts of meteorological variability and emission changes on O 3 changes over 2013-2020. O 3 concentrations exhibit obvious interannual increases during 2013-2019 and a slight decrease in 2020. Both decreases in the MEIC emission inventory (-2.9% yr -1 ) and OMI NO 2 column density (-3.1% yr -1 ) reflects the declining trend in NO x emissions over 2013-2020, while anthropogenic VOCs were not adequately regulated during 2013-2017, which explained the majority of deteriorated O 3 pollution from 2013 to 2017. Furthermore, attribution analysis based on CMAQ simulations indicate that the unexpected aggravated O 3 levels in 2019 is not only modulated by disproportional reductions in VOCs and NO x emissions, but also associated with unfavorable meteorological conditions featured by profound heatwaves and frequent stagnant conditions. In 2020, the abnormal meteorological conditions in May leads to substantial increase of O 3 by 26.8 μg m -3 as compared to May 2019, while the considerable enhancement was fully offset by low O 3 levels over the whole period which attributes to substantial emission reductions. This study reveals the long-term trend of O 3 levels and precursor emissions and highlights the effects of meteorological variability and emission changes on O 3 pollution over the SCB, with strong implications for designing effective O 3 control measures., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The Sichuan Basin (SCB) located in southwestern China has long been considered the most polluted city cluster with exposure to unhealthy levels of ozone (O 3 ) at times. However, the features of O 3 regional transport and source contributions in SCB are poorly understood. In this study, ambient measurements, ERA5 reanalysis dataset, IASI O 3 column, and the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) modeling system coupled with the Integrated Source Apportionment Method (ISAM) module were used to investigate the formation mechanism and sources of a severe O 3 episode in spring 2020 over the SCB. In the first stage of the O 3 episode, a high-pressure system persisted over the western SCB and caused northeasterly wind fields, leading to enhanced regional transport from the northern boundary with the O 3 contribution from the boundary exceeding 50% across the SCB. As the synoptic pattern evolved, southeasterly winds dominated the SCB and the stagnant zone over the Chengdu Plain confined O 3 originating from the southern SCB and Chongqing city, leading to the accumulation of precursors and elevated O 3 levels. During the O 3 episode, transportation and industrial sources were major contributors to O 3 formation especially for the Chengdu Plain and Chongqing city. In addition, the O 3 -rich air mass in the nocturnal residual layer that formed over Chongqing city was transported to the Chengdu Plain through southeastern corridor at 400-1600m above ground-level under the prevailing southeasterly winds. With sunrise and the development of the atmospheric boundary layer, the O 3 -rich air mass in the residual layer (RL) was entrained to the ground-level via vertical mixing, which further enhanced O 3 pollution across the Chengdu Plain. Our results revealed the mechanism of regional transport via northeastern and southeastern corridors during an O 3 episode and demonstrated the need for joint emission regulation across the SCB to mitigate O 3 pollution., 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 © 2021 Elsevier Ltd. All rights reserved.)

Visibility has been continuously and stably observed for more than half a century, while particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM 2.5 ) was not introduced to the national monitoring system in China until 2013. It is a scientific issue as to whether visibility can be used as an alternative to assess the health risks of air pollution in periods and areas without pollutant monitoring data. A generalized additive model (GAM) was adopted to estimate the impacts of seasonal changes in visibility on mortality in Beijing, China. Moreover, we estimated the contributions of particulate matter in the health effects of visibility by adjusting for dry extinction coefficient (β dryext ) and PM 2.5 in the model, respectively. We found that the acute health impacts of visibility varied by season, with the highest risks in winter. For respiratory mortality, the effect estimates per 1 km decrease in visibility were 0.40% (95% CI: 0.17-0.62%) in spring, 0.10% (95% CI: -0.14-0.34%) in summer, 0.27% (95% CI: 0.09-0.45%) in autumn, and 0.62% (95% CI: 0.38-0.85%) in winter. For cardiovascular mortality, the effect estimates per 1 km decrease in visibility were 0.20% (95% CI: 0.08-0.31%) in spring, 0.16% (95% CI: 0.04-0.27%) in summer, 0.25% (95% CI: 0.13-0.37%) in autumn, and 0.24% (95% CI: 0.13-0.35%) in winter. The seasonal pattern of health impacts related to visibility reflected the seasonal variations in the characteristics of air pollution emission sources and meteorological conditions that are unfavorable for pollutant dispersion. Particulate matter, particularly PM 2.5 , made significant contributions to the health impacts of visibility. The results indicated that controlling pollutant emissions in winter would be of significant importance to improve air quality and mitigate the health hazard of air pollution in Beijing. Our study also provides further evidence on the feasibility of using visibility to assess the health impacts of particulate matter pollution., 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 © 2020 Elsevier B.V. All rights reserved.)

Exposure to particulate matter of smaller than 2.5 μm in diameter (PM 2.5 ) is linked to increased human mortality, and could be further complicated by concurrent ambient air temperatures. Published reports indicate that the association between ambient temperatures and mortality due to PM 2.5 exposure is dissimilar across different geographic areas. Thus, it is unclear how ambient temperatures at different geographic locations can together modulate the influence of PM 2.5 on mortality. In this paper, we examined how temperature modulated the association between mortality and PM 2.5 exposure in 15 Chinese cities during 2014-2016. For analysis, First, Poisson generalized additive models under different temperature stratifications (<10th, 10-90th, and >90th temperature percentiles) was used to estimate PM 2.5 associations to mortality, which were specific to different cities. Second, we used a meta-analysis to combine the effects at each temperature stratum and region (southern and northern China). Results revealed that high temperatures (daily mean temperature >90th percentile) robustly amplified observed associations of mortality and PM 2.5 exposure, and the modifications were heterogeneous geographically. In the northern regions, a 10 μg/m 3 increment in PM 2.5 was associated with 0.18%, 0.28%, and 1.54% increase in non-accidental mortalities and 0.33%, 0.39%, and 1.32% increase in cardiovascular mortalities at low, moderate, and high temperature levels, respectively. In the southern regions, a 10 μg/m 3 increment in PM 2.5 was associated with 0.52%, 0.62%, and 1.90% increase in non-accidental mortalities and 0.55%, 0.98%, and 2.25% increase in cardiovascular mortalities at low, moderate, and high temperature levels, respectively. It is concluded that temperature altered PM 2.5 -mortality associations in southern and northern China synergistically, but the effect was more pronounced in the south. Therefore, geography and temperature need to be considered when studying how PM 2.5 affects health., Competing Interests: Declaration of competing interestcoi We declare no competing interests. The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Previous studies of the residents' willingness to pay (WTP) for air quality improvement are likely suffering various endogeneity biases. Exploiting the unique opportunity of a recent quasi-experiment operation of the world's first SFT (Smog Free Tower) in China's northwestern city Xi'an, this paper reliably calibrates local residents' WTP for less exposure to haze by analyzing the price responses of housings in the neighborhoods of SFT. The hedonic regression is applied in the DID (difference-in-difference) setting, with further assistances of the PSM (propensity score matching) method, quantile regression and placebo test. The regression results consistently suggest that housing price responded positively to the installment of the SFT, and the impact estimates are closely centered around 4%. The study also indicates high-priced housings response much more to the operation of the SFT than cheap-priced housings, suggesting uneven distribution of welfare gains of air quality improvement. A cost-benefit analysis of the SFT project indicates that the economic benefits of this project far outweigh the costs involved. The paper concludes with discussions of policy implications of this paper for environment governance., Competing Interests: Declaration of competing interests 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. The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:, (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Numerous studies have examined the correlation between economic growth and air pollution, but few focuses on the nexus between environmental regulation and <2.5 μm (PM 2.5 ) fine particle matter. Using Spatial Durbin Model (SDM) and Spatial Two-stage Least Squares (2SLS) methods to analyze 277 Chinese cities over the period 2002-2010, this paper finds inverted U-shaped relationships between PM 2.5 concentration and formal/informal environmental regulations for the whole and eastern and western regions. By removing the depression year of 2008, regulation effect on pollution strengthened, indicating that the main task for local governments in crisis is to avoid GDP decline rather than official promotion. Further, green technological innovation and industrial structure optimization induced by environmental regulation is shown to be beneficial for haze pollution mitigation. Some policy recommendations are proposed in conclusion., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The alternative transportation strategy implemented during the 2008 Summer Olympic Games in Beijing provided an opportunity to study the impact of the control measures and weather conditions on air quality and asthma morbidity. An ecological study compared the 41 days of the Olympic Games (8 August-17 September 2008) to a baseline period (1-30 June). Also, in order to emphasize the impact of weather conditions on air quality, a pollution linking meteorological index (Plam) was introduced to represent the air pollution meteorological condition. Our study showed that the average number of outpatient visits for asthma was 12.5 per day at baseline and 7.3 per day during the Olympics-a 41.6% overall decrease. Compared with the baseline, the Games were associated with a significant reduction in asthma visits (RR 0.58, 95%CI: 0.52-0.65). At 16.5 visits per day, asthma visits were also significantly higher, during the pre-Olympic period (RR 1.32, 95% CI: 1.15-1.52). The study also showed that the RR of asthma events on a given day, as well as the average daily peak ozone concentration during the preceding 48-72 h, increased at cumulative ozone concentrations of 70 to 100 ppb and 100 ppb or more compared with ozone concentrations of less than 70 ppb (P < 0.05). We concluded that along with "good" weather conditions, efforts to reduce traffic congestion in Beijing during the Olympic Games were associated with a prolonged reduction in air pollution and significantly lower rates of adult asthma events. These data provide support for efforts to reduce air pollution and improve health via reductions in motor vehicle traffic.

Severe outdoor haze pollution has brought about associated public health impacts for China in recent years. Haze pollution therefore has become one of the most serious environmental problems in China. To alleviate this, the government issued its National Air Pollution Control NACAP (NAPCAP) in 2013 containing pollution reduction targets for 2017 and beyond. However, there are doubts whether these targets can be achieved. This paper examines this issue by modeling the statistical relationship between PM 2.5 concentration and air pollutant emissions (SO 2 , NO x , etc.), together with wind and neighboring transfer impacts at the city level, to identify ways of calculating intended maximum emission levels in the Beijing-Tianjin-Hebei area. The results indicate that local air pollutant emissions, lagged PM 2.5 concentrations, wind speed, and PM 2.5 concentrations in adjacent areas have a significant impact on PM 2.5 concentrations in the Beijing-Tianjin-Hebei area. The 2017 haze concentration control targets could not be achieved through the current NAPCAP plan, with PM 2.5 concentration levels in many locations being predicted as between two and three times those targeted. However, the 2017 concentration target can be fulfilled given the pollutant reduction rates of NAPCAP plus Enhanced Measures of Air Pollution Control for Beijing-Tianjin-Hebei region (EMAPC) under the same wind conditions as 2016. There are large deviations between the simulation and monitor values of PM 2.5 concentration when it is less windy, and the simulation value of most cities are generally lower than the monitor values. The unsuccessful implementation of pollutant reduction measures and inaccuracy of the monitor data are two possible reasons to explain the relatively large deviations involved. Finally, some preliminary institutional causes of haze pollution and solutions for its control in the Beijing-Tianjin-Hebei area are discussed. [ABSTRACT FROM AUTHOR]

This paper presents an energy-environment-economy model that described technology-specific information and integrated resource depletion to simulate China’s long-term CO 2 emissions and economic development under fossil fuel supply constraints towards 2050. The modeling approach and findings not only support the theoretical of relationship between physical resources depletion and economic growth to some extent, but also provide practical significance for policy making that can be shared with other developing countries. The results indicate that energy supply constraints will play a crucial role in China’s future economic development, causing a 7.9% decrease in GDP compared to the 2050 baseline and a peak of CO 2 emissions at 11.2 Gt around 2034 under a resource constraint scenario, which can be considered as a new baseline considering fossil fuel depletion. Moreover, under a low carbon scenario considering low carbon measures, economic growth is less dependent on fossil fuel consumption, and CO 2 emissions will peak earlier in 2030, and the negative impact on GDP from finite fossil fuel supply can be alleviated by 5.5% by 2050. The low carbon scenario is a good way to achieve both CO 2 mitigation and low-carbon growth, which may lead to a complete restructuring of the China’s energy-economic system. To achieve the economic restructure towards low carbon economy, Chinese government should take into account the crucial role of fossil fuels supply constraints, set reasonable and moderate future GDP growth targets, and strictly implement the low carbon measures including accelerating technical progress, non-fossil fuel development, energy structure improvement and the upgrading of industrial structure and household consumption patterns. [ABSTRACT FROM AUTHOR]

Along with China's modern industrialization, challenges on smog crisis are raising dramatically in the past decade. The sources of municipal smog are multiple and complex, one of which is construction dust emission due to the rapid urbanization. In literature, there are studies focusing on the end-pipe treatment of construction dust; however, very little research has been conducted from the perspective of dust mitigation in developing countries. To fill in this research gap, this paper investigates the current situation of construction dust prevention and control in China, with the aim of providing insights for mitigating dust pollution caused by the construction industry. Through a combination of the content analysis, on-site observation, questionnaire survey and interviews with experienced professionals, a total of 11 related regulations are thoroughly reviewed, and the main sources of construction dust production are identified. A case study is further presented to demonstrate the prevailing dust control measures on site. Recommendations are proposed in order to increase the awareness of related stakeholders, including formulation of targeted regulations, establishment of an appropriate charging scheme, development of a feasible monitoring system, and enhancement of training and dissemination. [ABSTRACT FROM AUTHOR]

Abstract: Air pollution problems caused from the development of infrastructures are getting serious, in which air flow is reduced and heat is trapped among high-rise buildings. In order to mitigate these problems, various methods have been developed in previous studies. Extensive green roof has been identified as one of the most important means to mitigate these problems and implement sustainable development principles in the building features. Governments world-wide have been introducing various policies and regulations for promoting extensive green roof particularly for building projects. However, the existing buildings in many large cities such as Hong Kong display few extensive green roof features. Hong Kong is one of the most densely populated cities with many high-rise buildings. This paper examines the major barriers encountered in promoting extensive green roof systems for the existing buildings in Hong Kong. Case study approach is adopted to investigate how and why the barriers can hinder the implementation of extensive green roof features. Research results show that lack of promotion and incentives from governments and the increase maintenance cost are identified as the top barriers to the implementation. The paper concludes by providing further suggestions and actions that can help mitigate these existing barriers. [Copyright &y& Elsevier]

Three years of measurement of PM2.5 with 5-min time resolution was conducted from 2005 to 2007 in urban and rural environments in Beijing to study the seasonal and diurnal variations in PM2.5 concentration. Pronounced seasonal variation was observed in the urban area, with the highest concentrations typically observed in the winter and the lowest concentrations generally found in the summer. In the rural area, the maximum in PM2.5 concentration usually appeared during the spring, followed by a second maximum in the summer, while the minimum generally occurred in the winter. Significant diurnal variations in PM2.5 concentration were observed in both urban and rural areas. In the urban area, the PM2.5 concentration displays a bimodal pattern, with peaks between 7:00 and 8:00 a.m. and between 7:00 and 11:00 p.m. The minimum generally appears around noon. The morning peak is attributed to enhanced anthropogenic activity during rush hours. The decreases of boundary layer height and wind speed in the afternoon companying with increased source activity during the afternoon rush hour result in the highest PM2.5 concentration during evening hours. In the rural area, the PM2.5 concentration shows a unimodal pattern with a significant peak between 5:00 and 11:00 p.m. The seasonal and diurnal variations in PM2.5 concentration in the urban area are mostly dominated by the seasonal and diurnal variability of boundary layer and source emissions. The year-to-year variability of rainfall also has an important influence on the seasonal variation of PM2.5 in the urban area. The seasonal and diurnal wind patterns are more important factors for PM2.5 variation in the rural area. Southerly winds carry pollutants emitted in southern urban areas northward and significantly enhance the PM2.5 concentration level in the rural area. [Copyright &y& Elsevier]

Previous studies indicated that exposure to air pollution was associated with the progress of atherosclerosis, but evidence is very limited in China and even in the world. This study aims to assess the associations of long-term exposures to air pollution and greenness with the occurrence of carotid plaque. Participants of this cohort study were urban residents and office workers who visited Hebei General Hospital for routine physical examination annually from September 2016 through to December 2018. Eligible participants were people diagnosed the absence of carotid plaque clinically at their first hospital visit and were followed up at their second or third hospital visit. Exposure to particulate matter with aerodynamic diameter less than 2.5 μm (PM 2.5), nitrogen dioxide (NO 2) and ozone (O 3) were estimated using an inverse distance weighted (IDW) method. The level of greenness was assessed using the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI). The associations were evaluated using Cox proportional hazards regression models. Among 4,137 participants, 575 showed the occurrence of carotid plaque during the follow-up period. After controlling for potential confounders, the hazard ratios (HRs) and 95% confidence intervals (95%CIs) of carotid plaque associated with per interquartile range (IQR) increase in PM 2.5 , NO 2 , and O 3 were 1.78 (1.55, 2.03), 1.32 (1.14, 1.53) and 1.99 (1.71, 2.31), respectively. Increased EVI and NDVI were significantly associated with lower risk of carotid plaque [HR (and 95%CI): 0.84 (0.77, 0.93) and 0.87 (0.80, 0.94)]. PM 2.5 significantly mediated 80.47% or 93.00% of the estimated association between EVI or NDVI and carotid plaque. In light of the significant associations between air pollution, greenness and carotid plaque in this study, continued efforts are needed to curb air pollution and plan more green space considering their effects on vascular disease. Image 1 • Higher air pollution was associated with higher risk of carotid plaque. • Higher greenness was associated with lower risk of carotid plaque. • PM 2.5 significantly mediated the association of greenness with carotid plaque. [ABSTRACT FROM AUTHOR]

• Bivariate LISA statistic is effective to reveal the city typologies. • L pgdp H pm2.5 cities have 60% more coal-fired power plants than L pgdp H pm2.5 cities. • L pgdp H pm2.5 cities have 2.3 times as many iron and steel plants as L pgdp H pm2.5 cities. • Local economic transition benefits for nearby air quality in northern cities of China. • Air pollution policies should consider city typologies instead of being uniform over China. Air quality has proven to be closely related to economic levels. China is a vast country with substantial economic level and air quality disparities among cities. Consequently, policy-makers face challenges in implementing regional collaborative governances. Here, we use the bivariate local indicator of spatial association (LISA) statistic to reveal the spatial heterogeneous relationship between local per capita GDP and nearby air quality, especially fine particulate matter (PM 2.5). This study was conducted in 256 prefecture-level cities for the year 2015. The results show that 20, 28, 30, 28, and 187 cities were identified as the H pcgdp H pm2.5 , L pcgdp L pm2.5 , L pcgdp H pm2.5 , H pcgdp L pm2.5 , and 'not significant' typologies, respectively. Furthermore, L pgdp H pm2.5 cities are mainly located in the northern China, whereas H pcgdp L pm2.5 cities are mainly distributed in the Guangdong provinces. The underlying causes may be attributed to the differences in economic structures. We found that L pgdp H pm2.5 cities has approximate 60% more coal-fired power plants, 2.3 times iron and steel plants than those of H pgdp L pm2.5 cities, whereas the latter attracted 5.1 times as much investment capitals from foreign, Hong Kong, Macao and Taiwan as the former. This indicates the industries of H pgdp L pm2.5 cities have higher technology levels and lower emission intensities. Thus, policy makers should accelerate economic transformation, especially in Shandong, Hebei, and Henan provinces. Overall, our findings suggest that not only bivariate LISA statistic is a simple and useful approach to distinguish city typologies, but also provide the evidences for those cities responsible for air quality of adjacent cities. [ABSTRACT FROM AUTHOR]

Surface particulate matter with an aerodynamic diameter of <2.5 μm (PM2.5) and column-integrated aerosol optical depth (AOD) exhibits substantial diurnal, daily, and yearly variabilities that are regionally dependent. The diversity of these temporal variabilities in urban and rural areas may imply the inherent mechanisms. A novel time-series analysis tool developed by Facebook, Prophet, is used to investigate the holiday, seasonal, and inter-annual patterns of PM2.5 and AOD at a rural station (RU) and an urban station (UR) in Beijing. PM2.5 shows a coherent decreasing tendency at both stations during 2014–2018, consistent with the implementation of the air pollution action plan at the end of 2013. RU is characterized by similar seasonal variations of AOD and PM2.5, with the lowest values in winter and the highest in summer, which is opposite that at UR with maximum AOD, but minimum PM2.5 in summer and minimum AOD, but maximum PM2.5 in winter. During the National Day holiday (1–7 October), both AOD and PM2.5 holiday components regularly shift from negative to positive departures, and the turning point generally occurs on October 4. AODs at both stations steadily increase throughout the daytime, which is most striking in winter. A morning rush hour peak of PM2.5 (7:00–9:00 local standard time (LST)) and a second peak at night (23:00 LST) are observed at UR. PM2.5 at RU often reaches minima (maxima) at around 12:00 LST (19:00 LST), about four hours later (earlier) than UR. The ratio of PM2.5 to AOD (η) shows a decreasing tendency at both stations in the last four years, indicating a profound impact of the air quality control program. η at RU always begins to increase about 1–2 h earlier than that at UR during the daytime. Large spatial and temporal variations of η suggest that caution should be observed in the estimation of PM2.5 from AOD. [ABSTRACT FROM AUTHOR]

Abstract North China Plain (NCP) is one of heavily polluted regions that is characterized by a mixture of a myriad of anthropogenic and natural aerosols. A substantial spatial and temporal variations of aerosols and their compositions there poses a good testbed for the validation of model simulations. Aerosol optical depth (AOD) and PM 2.5 (particulate matter with aerodynamic diameter < 2.5 μm) concentration products from the Modern Era Retrospective-Analysis for Research and Applications, version 2 (MERRA-2) are evaluated using available independent ground-based in situ and remote sensing products in the NCP. The comparison of MERRA-2 aerosol species to the observations is also performed. Although several satellite and ground-based AOD products are assimilated into the MERRA-2, MERRA-2 AOD is systematically smaller than independent sunphotometer measurements. The biases range from 0.09 (13%) in the summer to 0.17 (33%) in the spring and show little spatial dependence. Daytime AOD variations are captured by the MERRA-2, although MERRA-2 has relatively lower AOD. MERRA-2 produces lower PM 2.5 concentration relative to surface measurements in all seasons except in summer. The largest bias is found in the winter (44 μgm−3). On the contrary, summer MERRA-2 PM 2.5 is close to surface-measured PM 2.5 (with bias of 0.4 μgm−3). MERRA-2 was unable to reproduce diurnal PM 2.5 variation. Evaluation of MERRA-2 aerosol species in the winter of 2014 suggests that MERRA-2 could not keep track of dramatic day-to-day variation of aerosols and their species. Potential causes for this deficiency may include a lack of nitrate aerosols (accounting for 20% of PM 2.5 concentrations during heavily polluted days). This fault cannot be remedied by assimilation of satellite AODs because they are often missing. Highlights • MERRA-2 underestimates AOD but produces consistent daytime variation as sunphotometer data. • MERRA-2 produces extremely lower PM 2.5 concentration relative to surface measurements in the winter. • Assimilation of satellite AOD cannot remedy MERRA-2 PM 2.5 error associated with lack of nitrate simulation. • Missing satellite AOD product during haze episodes needs further consideration. [ABSTRACT FROM AUTHOR]

It's urgent to clarify the quantitative relationship between declining fine−particle (PM 2.5) concentrations and increasing ozone (O 3) levels as ozone pollution is increasingly severe in China. Here, we analyze the ground–based data of aerosol optical properties, particulates, and gaseous pollutants collected in a simultaneous observation in Kunming, locate in the Yunnan–Guizhou Plateau, from June 2014 to May 2017. The data exhibit slightly rising levels of PM 2.5 , O 3 , and carbon monoxid (CO), declining AOD (aerosol optical depth) but increasing AE (Angstrom exponent). Both the seasonal PM 2.5 and CO concentrations were low in the wet season and high in the dry season. The seasonal ozone levels and AE almost increased monotonically while the seasonal AOD decreased wavelike. Overall, the maximum daily 8 h average (MDA8) O 3 concentrations positively related to PM 2.5 concentrations with temperature>22 °C, RH<45%, and AOD<1.0 in the wet season. Generally, MDA8 O 3 concentrations didn't fluctuate with PM 2.5 concentrations in the dry season. High SSA (single scattering albedo) corresponded to high MDA8 O 3 concentrations and low SSA corresponded to low MDA8 O 3 concentrations in the wet season. However, lower SSA values in the dry season were observable. Most high MDA8 O 3 concentrations (>100 μg m−3) in the wet season occurred with AE at 1.0–1.5. High MDA8 O 3 concentrations (>100 μg m−3) in dry season appeared with an AE range of ~0.75–1.75. Low MDA8 O 3 concentrations occurred with AOD>2.0 and RH>75%, despite T>20 °C. The biomass−burning/urban aerosols were dominant (71.11% in the wet season and 74.40% in the dry season). The PSCF (Potential Source Contribution Function) results revealed the air pollutants from inside and outside China will have great impacts on the pollutant levels in Kunming besides the local emissions. Particularly, the severe pollution in India may aggravate Kunming's air pollution. • High SSA corresponded to high MDA8 O 3 concentrations and positive MDA8 O 3 − PM 2.5 relations were observable with SSA>0.95. • Most high MDA8 O 3 concentrations (>100 μg m−3) in the wet season occurred with AE at 1.0–1.5. • Biomass−burning/urban aerosols were dominant, accounting for over 70% of the whole aerosol types. • The air pollutants from outside China may have an important impact on the pollutant levels in Kunming. [ABSTRACT FROM AUTHOR]

Both PM 2.5 and visibility are important physical parameters to measure the air pollution condition. This paper first provided a new normalization approach for the relationship between PM 2.5 and visibility in heavy pollutant region, which realized a mathematical calculation for two different physical parameters based on non-dimensional data process (also called Min-Max normalization). The normalization relationship showed a power function (y = axb) with high correlation coefficients. The inflection points of the maximum power function curvature composed the theoretical threshold range of PM 2.5 for improving or deteriorating the visibility. In the case city of north China, the threshold range of PM 2.5 was 112–121 μg·m−3 corresponding to the visibility range 4.5–5.9 km. Within the threshold range, the mean concentration of main pollutant components was 106 μg·m−3. The mean extinction coefficient, b ext of 743.5 Mm−1, was mainly contributed by organic matter (34%), ammonium nitrate (19%), ammonium sulfate (18%) and elemental carbon (13%). When PM 2.5 was below the range, the visibility increased significantly with the slow decrease of PM 2.5. When PM 2.5 exceeded the range, the visibility reduced seriously due to the saturated extinction contribution of the main pollutants. The new normalization approach theoretically revealed the significance of threshold and how to improve visibility by controlling PM 2.5 at different pollution stages. Unlabelled Image • A new normalization approach was first applied to establish the mathematical relationship of PM 2.5 and visibility. • The normalization mathematical relationship was a power function with high correlation coefficients. • The maximum curvature of the function composed the theoretical threshold of PM 2.5 to improve or deteriorate visibility. • The extinction coefficients of aerosol components were quite different at different pollution stages. • The threshold range has guiding significance how to control PM 2.5 for the blue sky in heavy polluted cities. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) play key roles in the formation of particulate matter (PM) and oxidants and hence enhance the summertime air pollution. With data analysis from various field observations (urban station: Haidian, HD; suburb station: Changping, CP; regional background station: Shangdianzi, SDZ) in June 2011, we found that the mean O 3 concentrations throughout the observation period can be arranged in order: SDZ＞CP＞HD. The mean PM concentrations can be arranged in order: HD＞CP＞SDZ. The mean concentration of total VOCs at HD was close to that at CP, but much higher than that at SDZ. Oxygenated volatile organic compounds (OVOCs) made the largest portion of VOCs (~40%) at the three stations, followed by alkanes and alkenes. Good positive correlations between the concentrations of PM and O x (=O 3 ＋NO 2) at high air temperature (≥30 °C at HD and CP; ≥28 °C at SDZ) and low RH (≤60%) were found in the daytime (07:00–18:00 LT). However, the PM concentrations were partly negatively correlated with O x at lower temperatures (≤26 °C at HD and CP; ≤22 °C at SDZ) and higher RH (≥80%). The PM concentrations were found either positively (HD and CP) or negatively (SDZ) correlated with aromatics at high temperature and low RH. The aging degree of air masses at the three stations can be arranged in order: SDZ＞CP＞HD. This can qualitatively explain the different PM−aromatics correlations. Our data suggested the other groups of VOCs may promote the increase of PM concentrations unless the PM levels become higher than 140 μg m−3 under humid conditions. This study confirms the importance of VOCs in the formation of summertime PM and oxidants over Beijing. Image 1 • Parallel photochemical formations of PM and O 3 caused positive PM-O x correlations. • Positive PM-aromatics correlations were found at HD and CP, but negative at SDZ. • OVOCs made the largest portion of VOCs (~40%) in the high ozone episode. • VOCs may promote the increase of summertime PM concentrations under humid conditions. [ABSTRACT FROM AUTHOR]

Visibility can be used as a highly relevant visual indicator of the air pollution level. Published data on the correlations between visibility and health outcomes are very limited in China, and the health effects of slight haze on the human body have not been clarified. A semi-parametric generalized additive model (GAM) was used to assess the acute health effects of visibility on respiratory–cardiovascular mortality in Beijing, China. The correlation between visibility and PM 2.5 as well as the contributions of PM 2.5 to the health effects of visibility were analysed. Stratification model was employed to investigate the health effects of slight haze. The mortality risk of impaired visibility on the current exposure day peaked and was statistically significant for all the mortality outcomes. Every 1 km decrease in visibility corresponded to a 0.78% (95% CI: 0.62–0.95%) increase in total respiratory mortality and 0.54% (95% CI: 0.45–0.61%) increase in total cardiovascular mortality. Older people (age ≥65) were at a higher risk than the younger age group under impaired visibility. PM 2.5 had a negative logarithmic relationship relative to visibility. After adjustment for PM 2.5 , the risk estimates for both respiratory and cardiovascular mortality reduced. Short-term exposure to low visibility was significantly associated with increased respiratory and cardiovascular mortality in Beijing. The health risk of impaired visibility was particularly high, even in slight haze. The hazardous effects of visibility can be partially attributed to the effects of PM 2.5. These results can provide useful reference for relevant agencies to determine whether an adjustment to the haze warning level is warranted. Our findings indicate that visibility can be used as an alternative indicator for air quality assessments if air pollution data are insufficient or not available, particularly in developing countries. Image 1 • Studies on association between visibility and health outcomes are rare in China. • Exposure to impaired visibility is significantly related to increased mortality. • Health effects of impaired visibility can be partially explained by PM 2.5. • Health risk of impaired visibility is intense, even in slight haze. [ABSTRACT FROM AUTHOR]

Spatiotemporal patterns of global air pollution are of great significance to environmental management and public health. Studies have revealed the changes in the concentration of dust and sea-salt removed fine particulate matter (PM 2.5) pollution (DSRPP). However, the spatial characteristics of DSRPP on multiple scales remain unclear. Therefore, we combined the latest global estimates of the PM 2.5 dataset and landscape metrics to investigate the spatiotemporal patterns of DSRPP across global and national scales from 2000 to 2016. We found that the area of DSRPP increased from 1,146,800 km2 to 3,929,800 km2 between 2000 and 2016, a factor of 2.43. The DSRPP became more structurally fragmented and geometrically complex, with the patch density and the landscape shape index of DSRPP increasing by 133.3% and 24.5%, respectively. More than 90% of the DSRPP were concentrated in the middle income countries, especially in India and China. Specifically, the DSRPP in China exhibited a sprawling process before 2007 but a dissipating process after 2007 under the great efforts of the Chinese government in mitigating air pollution, while DSRPP in India remained an aggregation trend. The potential threat to public health posed by the DSRPP increased over time. Populations living in the areas with the DSRPP increased by 141.2% from 2000 to 2016 due to the deterioration of air quality and demographic change. Thus, we suggest that effective actions should be taken to control the main sources of anthropogenic emissions and mitigate the negative effects of DSRPP on public health in the future, especially in the middle income countries such as China and India. Image 1 • The area of global DSRPP increased by a factor of 2.43 from 2000 to 2016. • The global DSRPP became more spatially fragmented and complex from 2000 to 2016. • China's DSRPP sprawled before 2007 but dissipated thereafter through emission control. • The threat of global DSRPP to public health increased over time. [ABSTRACT FROM AUTHOR]