Megacity In China Research Articles

Differentiating the Contributions of Particle Concentration, Humidity, and Hygroscopicity to Aerosol Light Scattering at Three Sites in China

AbstractThe scattering of light by aerosol particles dictates atmospheric visibility, which is a straightforward indicator of air quality. It is affected by numerous factors, such as particle number size distribution, particle mass concentration (PM2.5), ambient relative humidity (RH), and chemical composition. The latter two factors jointly influence the aerosol liquid water content (ALWC). Here, the particle backscattering coefficient (βp) under ambient RH conditions is investigated to differentiate and quantify the contributions of aerosol properties and meteorology using comprehensive observational datasets acquired at three megacities in China, that is, Beijing (BJ), Nanjing (NJ), and Guangzhou (GZ). Overall, the temporal variations in βp under ambient RH conditions are consistent with those in ALWC at the three sites. The PM2.5 in BJ is systematically higher than in NJ and GZ, while ambient RH and aerosol hygroscopicity in NJ are much higher than in BJ and GZ. Notable differences in the variations of βp with related factors at the three sites are demonstrated. βp is more sensitive to particle hygroscopicity and mass in NJ and ambient RH in BJ. The relative contributions of these factors to βp at the three sites under different pollution conditions are differentiated and quantified. The factor with the largest impact on the variability in βp shifts from particle mass to ambient RH as air quality deteriorated to heavy pollution in BJ. The opposite is true in NJ. In GZ, the contributions of these factors to changes in βp under different pollution conditions are similar, both dominated by PM2.5.

Real-time, single-particle chemical composition, volatility and mixing state measurements of urban aerosol particles in southwest China

To investigate the volatility of atmospheric particulates and the evolution of other particulate properties (chemical composition, particle size distribution and mixing state) with temperature, a thermodenuder coupled with a single particle aerosol mass spectrometer was used to conduct continuous observations of atmospheric fine particles in Chengdu, southwest China. Because of their complex sources and secondary reaction processes, the average mass spectra of single particles contained a variety of chemical components (including organic, inorganic and metal species). When the temperature rose from room temperature to 280°C, the relative areas of volatile and semi-volatile components decreased, while the relative areas of less or non-volatile components increased. Most (> 80%) nitrate and sulfate existed in the form of NH4NO3 and (NH4)2SO4, and their volatilization temperatures were 50–100°C and 150–280°C, respectively. The contribution of biomass burning (BB) and vehicle emission (VE) particles increased significantly at 280°C, which emphasized the important role of regional biomass burning and local motor vehicle emissions to the core of particles. With the increase in temperature, the particle size of the particles coated with volatile or semi-volatile components was reduced, and their mixing with secondary inorganic components was significantly weakened. The formation of K-nitrate (KNO3) and K-sulfate (KSO4) particles was dominated by liquid-phase processes and photochemical reactions, respectively. Reducing KNO3 and BB particles is the key to improving visibility. These new results are helpful towards better understanding the initial sources, pollution formation mechanisms and climatic effects of fine particulate matter in this megacity in southwest China.

The impacts of weather conditions on metro ridership: An empirical study from three mega cities in China

Understanding the impacts of weather conditions on metro ridership can provide insights to improve the resilience of metro systems. However, there are few studies to examine the weather-metro ridership relationship in multiple cities with a framework to obtain generalizable and robust results. This study aims to fill this gap by establishing reliable models to investigate the impacts of weather conditions on metro ridership in three mega cities with different weather conditions in China, namely Beijing, Shanghai and Shenzhen. We collect daily metro ridership and weather parameters of three cities for a 12 month period in 2019, and the multiple linear regression models with 9-term moving average are utilized to investigate the weather-metro ridership relationship in each city. The metro ridership residual is selected as the dependent variable, and independent variables include weather variables, seasonal variables, comprehensive comfort index and air quality index. In addition, socioeconomic characteristics are also considered in the generalized linear mixed-effect models with multiple cities. Results highlight that independent variables have significant impacts on metro ridership in all models. Although significances of variables are various in different models, most variables have the same influence direction in different models on both weekdays and weekends. As a whole, temperature residual, spring, summer, and fall have a positive impact on metro ridership, while relative humidity residual, wind speed residual, and precipitation are negatively associated with metro ridership. Besides, the ridership on weekends is more severely affected by weather conditions compared to that on weekdays. In the overall models, socioeconomic characteristics are significant on weekdays, but they are insignificant on weekends. It should be noted that the comprehensive comfort index and air quality index are significantly associated with metro ridership in specific models, and they should be considered in further weather-ridership modeling. The findings can deepen our understandings about weather-metro ridership relationship and the differences among cities, which would provide valuable information for scheduling and management of metro systems.

Air pollution risk assessment related to fossil fuel-driven vehicles in megacities in China by employing the Bayesian network coupled with the Fault Tree method

Vehicle emissions have become one of the key pollution sources affecting air quality and human health in China's megacities. How to curb excess vehicle emissions has become a key pain point of urban air pollution prevention and control. This work tries to explore an effective integrated approach/framework to quantitatively assess the risk factors of excess vehicle emissions (EVE) and their impact on air quality for China's typical megacities. Bayesian Network is employed as the assessment tool by coupling with the Fault Tree method to curb the above problem for the first time. Four megacities (Beijing, Tianjin, Hangzhou, and Guangzhou) in China are selected as case studies, and the risk factors leading to EVE are identified to construct the Bayesian Network model. At the same time, some accurate quantisation algorithms of the occurrence probability of root nodes were proposed for the target megacities from 2014 to 2019. The analysis results show that the variation trend of the probability of EVE has a good positive correlation with the variation trend of air quality in some megacities. From 2014 to 2019, the no-occurrence probability of EVE in Beijing, Tianjin, and Hangzhou increased from 0.4972, 0.4973, and 0.6314 to 0.6491, 0.6846, and 0.7564; the good air quality rate increased from 47.1%, 47.9%, and 59.2%–65.8%, 60%, and 78.6%. Based on the developing trend of the historical data/information and considering the impact of new energy vehicles, the no-occurrence probability of EVE in Beijing and Tianjin is predicted to be increased from 0.6888 to 0.7929 in 2020 to 0.8561 and 0.8645 in 2025. This work may provide a novel approach and perspective that can realise accurate traceability of key risk factors, quantitative risk assessment and prediction function of urban vehicle emissions for sustainable development of China's megacities.

Bioaccessibility and health risk assessment of trace metals in Nanjing park dust

The bioaccessibility, chemical fractions, and total concentrations of Hg, As, Mn, Ni, Cd, Cr, Cu, Pb and Zn were determined in 17 urban park dust samples collected from a megacity in China. The geoaccumulation index indicated heavy Hg pollution, moderate Cd pollution, and slight to moderate Cu, Pb and Zn pollution. The inhalation bioaccessibility measured by the Artificial Lysosomal Fluid method decreased in the order of Cd > Zn > Mn > Ni > Pb > As > Cr > Cu. The ingestion bioaccessibility measured by the Physiologically Based Extraction Test decreased in the order of Cd > Zn > Mn > Cu > Pb > As > Ni > Cr. The modified European Community Bureau of Reference method was used to extract the chemical fractions of trace metals. As (87%), Cr (87%), and Hg (99%) were predominantly found in residual fraction (F4), whereas Cd was predominantly found in water soluble and exchangeable fraction (F1 34%) and carbonate, oxidizable and reducible fraction (F2 27%). The first two chemical fractions of the trace metals were closely correlated with their bioaccessibilities. The carcinogenic and non-carcinogenic risks of exposure to trace metals in park dust were assessed using inhalation bioaccessibility and ingestion bioaccessibility. The hazard indexes of all investigated trace metals were below the safe level of 1. The carcinogenic risks of As, Ni, Cd and Cr were also below the acceptable level (10−6), indicating that there was no non-carcinogenic or carcinogenic risk from trace metals in the park dust.

A new method to explore the abnormal space of urban hidden dangers under epidemic outbreak and its prevention and control: A case study of Jinan City

AbstractIn recent years, the proliferation of coronavirus disease has profoundly affected the world. The vitality of urban space is difficult to recover in the short term. Therefore, in the early stage of human-to-human transmission of the epidemic, we need to determine the potential urban agglomeration space as soon as possible, the timely find of hidden danger areas, and carry out spatial optimization to prevent the further spread of the epidemic. This becomes the urgent problem at the moment. Jinan is the capital city of Shandong Province, and the mega-city of China. The study is focused on the main urban area within the bypass. This study used spatial data methods such as spatial grammar and GIS technology. First, we analyzed the spatial topological properties of urban road network during the epidemic. Then, we carried out spatial autocorrelation analysis on the topological attributes to get the shape of urban spatial clustering layout during the epidemic. Finally, the thesis crawled through various types of infrastructure points-of-interest and conducted nuclear density analysis to get the dynamic trend of urban space in Jinan. The research results showed that there is significant space for agglomeration in the main urban area of Jinan. The areas with strong agglomeration are basically located in tourism areas, school areas, business areas, living circle areas of residential communities in Licheng and Lixia districts, transportation hub areas in Tianqiao District, and high-tech industrial areas in Lixia District. Topography, water body, greening, and parks could effectively reduce the concentration of human flow, and are important areas to relieve the potential abnormal epidemic. This study provided a new method for detecting epidemic prevention and control areas, optimizing urban space layout and formulating prevention and control strategies in the early stage of human-to-human epidemic transmission and lack of case surveillance data and control measures.

Panacea or Pandora's Box? An institutional analysis of the contested long-term rental apartments development in China

The dramatic growth of long-term rental apartments (LRAs) in China's megacities since 2015, spurred by a series of state policies encouraging the development of the private rental sector (PRS), has culminated in many LRA firms encountering capital chain rupture and even going bankrupt within a short period. As a result, thousands of tenants were rendered homeless and many property owners were left unpaid. The present study analyses the boom and bust of LRA development in China under housing financialisation and explores the relationship between the transformative institutions – characterised by policy deregulation/re-regulation – and market performance stimulated by capital speculation. The findings of this study reveal the institutional changes in China's PRS to have been closely linked to the socio-economic changes emanated from endogenous opportunism and exogenous shocks. Specifically, the policy drift in the PRS was closely associated with deregulation and capital speculation, while policy layering was employed to institutionalise, regulate and legalise the PRS, thus mitigating the housing shortage crisis and ensuring the retention of social stability. Adapting to the volatile politico-economic circumstances as a form of punctuated equilibrium, policies governing the PRS require constant assessment and reflection to safeguard people's basic housing rights.

Winter brown carbon over six of China's megacities: light absorption, molecular characterization, and improved source apportionment revealed by multilayer perceptron neural network

Abstract. Brown carbon (BrC) constitutes a large fraction of organic carbon and exhibits strong light absorption properties, thus affecting the global radiation budget. In this study, we investigated the light absorption properties, chemical functional bonds, and sources of BrC in six megacities in China, namely Beijing, Harbin, Xi'an, Chengdu, Guangzhou, and Wuhan. The average values of the BrC light absorption coefficient and the mass absorption efficiency at 365 nm in northern cities were higher than those in southern cities by 2.5 and 1.8 times, respectively, demonstrating the abundance of BrC present in northern China's megacities. Fourier transform infrared (FT-IR) spectra revealed sharp and intense peaks at 1640, 1458–1385, and 1090–1030 cm−1, which were ascribed to aromatic phenols, confirming the contribution of primary emission sources (e.g., biomass burning and coal combustion) to BrC. In addition, we noted peaks at 860, 1280–1260, and 1640 cm−1, which were attributed to organonitrate and oxygenated phenolic groups, indicating that secondary BrC also existed in the six megacities. Positive matrix factorization (PMF) coupled with multilayer perceptron (MLP) neural network analysis was used to apportion the sources of BrC light absorption. The results showed that primary emissions (e.g., biomass burning, tailpipe emissions, and coal combustion) made a major contribution to BrC in the six megacities. However, secondary formation processes made a greater contribution to light absorption in the southern cities (17.9 %–21.2 %) than in the northern cities (2.1 %–10.2 %). These results can provide a basis for the more effective control of BrC to reduce its impacts on regional climates and human health.

Characterizing formation mechanisms of secondary aerosols on black carbon in a megacity in South China

Refractory black carbon (rBC) aerosols emitted from incomplete combustion are important climate forcers. Understanding the chemical characteristics and evolution of rBC-related components is particularly crucial to assess rBC environmental impacts. Here, we explored the chemical components of rBC in Shenzhen, China, using a soot-particle aerosol mass spectrometer (SP-AMS). The observations showed that the rBC coating was mainly composed of secondary aerosols with an average mass contribution of 84.7 %. Among them, secondary organic coating occupied ∼57.7 % of the total coating mass. Exploration of the relationship between secondary organic aerosol (SOA) coating and Ox (=NO2 + O3, an indicator of the extent of photochemical processing) showed that SOA coating was generated mainly through photochemical oxidation during the day. Similarly, sulfate coating, with a small mass fraction of 0.9 %, was also dominated by photochemical oxidation. In contrast, nitrate coating responded positively to ambient relative humidity, especially at night, indicating that it was driven by heterogeneous reactions. In addition, the increased ratio of nitrate on rBC to bulk nitrate at night suggested that black carbon surface could facilitate nocturnal nitrate formation.

Real-time variabilities in microplastic abundance and characteristics of urban surface runoff and sewer overflow in wet weather as impacted by land use and storm factors

Urban surface runoff (USR) and drainage system overflows during wet weather (WWF) play a key role in shaping water pollution. Particularly, the impact of large amounts of microplastic pollution on urban water bodies is unclear. We conducted an in-field investigation in six central urban drainage systems along Suzhou Creek in the Shanghai megacity of China and identified the impacts of storm factors and land use on the real-time dynamic changes in microplastic abundance and characteristics in USR and WWF. Microplastic abundances ranged from 228.3 ± 105.4–4969.51 ± 348.8, 309.3 ± 144.3–5195.8 ± 425.5, and 130.0 ± 30.0–8500.0 ± 1241.0 particles/L in the traffic and residential catchment USR, and the WWF, respectively. Under similar storm factor conditions, we observed correlations between environmental factors and microplastic abundance, especially the polymer type, verifying the significant role of land use. The microplastic abundance were 90.2 particles/L higher in the traffic catchment USR than in the residential catchment USR. Notably, we found unique microplastic polymers comprising ethylene vinyl acetate copolymer and thermoplastic elastomers in the residential and traffic catchment USR, respectively. However, land use had a minimum impact on the size and shape of microplastics: small-sized and film microplastics dominated in both USR types. We found statistical evidence of the widespread correlations between microplastic abundance and storm factors (accumulated storm depth and WWF flow) in both USR and WWF. The first flush phenomenon of microplastic dynamics was found in both USR and WWF. Microplastic characteristics also changed dynamically with storm time. With heavy storm factors, polypropylene and small-sized (<1 mm) microplastics in USR events increased and then decreased. This was also true for WWF events in granular and polyethylene terephthalate microplastics. Our results can facilitate the targeted mitigation of emerging pollutants to enhance stormwater management strategies and prevent future contamination.

Aquatic environmental fates and risks of benzotriazoles, benzothiazoles, and p-phenylenediamines in a catchment providing water to a megacity of China

Wearing of vehicle parts could release many chemical additives into the environment, such as benzotriazoles (BTRs), benzothiazoles (BTHs), and p-phenylenediamines (PPDs), which are potentially toxic to wildlife and humans. This study investigated the occurrence, source, and risks of BTRs, BTHs, and PPDs in a source catchment providing water to Guangzhou, a megacity in South China, covering groundwater, surface water, and stormwater. The results showed that BTRs and BTHs were predominant in surface water and groundwater. Unexpectedly, the BTR and BTH concentrations were lower in surface water than groundwater in a third of the paired samples. For the first time, 6PPD-quinone, a toxic ozonation product of N-(1,3-dimethylbutyl)-N′-phenyl-1,4-phenylenediamine (6PPD), was extensively detected in source waters. Stormwater decreased the BTR concentrations but increased the 6PPD-quinone concentrations in surface water owing to their affiliation to suspended particles. From natural to urban segments of Liuxi river, a downstream increasing trend in BTR and BTH concentrations was observed, confirming that they are indicative of urban anthropogenic activities. Strong correlations between industrial activities and BTR or BTH concentrations in surface water indicated that industrial activities were their main sources. Six compounds were prioritized as potentially persistent, mobile, and toxic (PMT) chemicals, combing our monitoring results and REACH criterion. This study improves our understanding of the environmental fates and risks of water-soluble tire-wear chemicals, which provides important information for chemical management, and indicates attention should be paid to the risk posed by 6PPD-quinone in the source water.

Seismogenic Structure and Tectonic Mechanism of the 2021 Mw 5.0 Yancheng Earthquake in the South Yellow Sea Basin, East Asia

AbstractOn 17 November 2021, a moment magnitude (Mw) 5.0 earthquake occurred off the Yancheng city in the South Yellow Sea. This earthquake has caused ground motions and been felt by people in a few megacities in east China, for example, Shanghai, Nanjing. However, due to limited seismic data, the focal fault and mechanism of this earthquake remain unknown. Here, we combine the seismic profiles, seismicity, focal mechanism, well data with regional tectonics to investigate the seismotectonics of this event and the possible role of fluid migration in triggering the earthquake. Our new results suggest that two sets of preexisting strike-slip faults were developed near the epicenter of the Yancheng earthquake, including the north–northeast-trending fault F1, the North Wunansha fault, and the northwest-trending fault F5. These preexisting faults have been reactivated entirely or partly with dextral and sinistral motions during the Miocene to Quaternary. Fault F1 runs through the epicenter of the Yancheng earthquake and is therefore interpreted to be the seismogenic fault. Various igneous complexes and associated hydrothermal vent complexes have been identified in the vicinity of the reactivated fault F1 and other strike-slip faults. Combined with the published igneous rock ages from nearby region, the igneous and hydrothermal activities were suggested to be continue until the Miocene and Quaternary, which are coincident with the reactivation of the preexisting strike-slip faults. The reactivation of the preexisting fault, and igneous and associated hydrothermal activities were suggested to be caused by the subduction of Pacific and Philippine Sea plates and collision of India and Eurasia plate. The hydrothermal fluids may have migrated through the preexisting fault F1 and other strike-slip faults, which enhanced the reactivation of these faults and in turn promoted the fault slip, eventually triggering the Yancheng earthquake and other historical events in the study area.

Study of the Hierarchical Relationships and Renovation of Support Systems in Existing Residential Areas in Shenzhen, China

The existing residential area in Shenzhen, China mainly refers to a specific multi-story brick and concrete residential area built in the 1980s-1990s. After 30-40 years of use, the structures in these settlements have experienced different degrees of deterioration. As a megacity in southern China, Shenzhen has engaged in a diversified transformation to maintain and renew existing residential area, including comprehensive environmental improvements, facade and roof transformations, elevator installations, and pipeline replacements. However, there has been a lack of systematic reviews of different renovation practices and their effects on existing residential areas. Based on concept of “ level ” from open buildings, this study reviews the hierarchical relationships in existing residential areas in Shenzhen, dividing the residential building support systems into four parts: the enclosed structures, components attached to facades, the public space in a building, and public pipelines. The study reviewed nine typical case settlements using field investigations and analysis, and summarized the mode and degree of the renovation or transformation, the rights and responsibilities of the subjects involved, and the purpose of the current support system elements. This facilitates a systematic review of the problems emerging during a renovation. This study provides a new perspective and theoretical basis for reviewing the renovation of existing residential areas in China.

Does urban green space justly improve public health and well-being? A case study of Tianjin, a megacity in China

Urban green space (UGS) planning and design can not only influence economic development and the ecological environment but also have a significant impact on urban public health. Facing the increasingly serious public health crisis in megacities, promoting environmental justice in UGS, and improving the health and well-being of urban residents have become critical issues to be addressed in response to the global urban sustainable development goals (SDGs). Using data from a survey of 682 residents in the central district of Tianjin, we constructed a structural equation model based on theoretical analyses of spatial justice, social stratification, and Rawls' theory to reveal injustices in the accessibility of health benefits of UGS among residents of different socioeconomic status (SES) and explore the ways in which SES affects residents' health and well-being via UGS. The results indicate that: (1) Increasing the intensity of green space exposure can improve residents' health and well-being, but due to the urban green space premium effect, inequities exist among residents of different SES in enjoying the health benefits of UGS, thus deepening health inequality in megacities. (2) SES can influence residents' health and well-being through three paths: “green premium mechanism”, “green exposure mechanism”, and “green chain mechanism”, and green space premium and green space exposure play a mediating role in the influence of SES on residents' health and well-being. (3) To promote environmental justice in UGS, provide urban human care, and guarantee public health equality, the UGS in China's megacities needs to be further explored in terms of UGS layout optimization, service quality improvement, and management system guarantee.

Measuring urban ecological network resilience: A disturbance scenario simulation method

Human disturbance of urban ecosystems is intensifying, as is ecological fragmentation. As such, effective connections between green spaces must be established and restored to form structurally resilient urban ecological networks. In this study, we focused on indicators of city-scale ecological network resilience. We constructed a network model, analyzed the disturbance simulation results, and identified key nodes. Shenzhen, a megacity in China was selected for empirical research. First, we used Floyd algorithm to extract least-cost paths and then generate the corridor network, constructing an ecological network model with 386 nodes and 4910 edges. Second, focusing on the nodes of the constructed ecological network, we adopted a selected attack strategy to conduct dynamic simulations, using two parameters, network efficiency and maximum connectivity, to evaluate the resilience of the ecological network to changes under various disturbance scenarios. The results showed that the ecological network structure in the study area was relatively stable, and the first 30 % of nodes substantially impacted network resilience. The outcomes reflect the state of urban ecosystems that have been disturbed by socio-economic systems and are practically important for formulating adaptive spatial planning and management policies.

Impact of climate change on coastal water quality and its interaction with pollution prevention efforts

The impact of climate change on nearshore coastal water quality and its interaction with pollution prevention efforts (e.g., the development of green and gray water infrastructure) still lack systematic investigation. This study performed a holistic analysis of the impact of climate change on the salinity and concentrations of total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl.a) in Shenzhen Bay between Shenzhen and Hong Kong, the two most developed megacities in South China, based on three-dimensional hydrodynamic and water quality modeling. The major study findings were as follows. First, Chl.a was the most sensitive parameter, and its bay-wide average concentration in 2100 was predicted to be approximately 13% and 46% higher than those in 2015 under mild and rapid climate change scenarios, respectively. Second, sea level rise was found to be a major driver of all four water quality parameters, while temperature and radiation mainly influenced Chl.a and precipitation mainly influenced nutrients. Third, water quality responses to climate change were highly heterogeneous over the bay. Even under a mild climate change scenario, the highest location-specific changes (2100 vs. 2015) in salinity and TN, TP and Chl.a concentrations were projected to be approximately 21%, 19%, 25%, and 65%, respectively. Fourth, changes in seasonal variation due to climate change may lead to an enhanced ecological risk of algal blooms. Finally, the effect of reducing TN and TP concentrations by proposed water infrastructure development was found to be significantly weakened (nearly 40% and 20% for TN and TP, respectively, under a mild climate change scenario), while the negative effect (i.e., increase in the Chl.a concentration) was notably accelerated. Regional cooperation is critical for protecting the water quality of the bay, particularly under climate change. The insights obtained in this study are applicable to other coastal water zones around the world with similar socioeconomic backgrounds and climatic conditions.

Leverage of resource efficiency over environmental emissions: Case of a megacity in China

Material metabolism in a Chinese megacity, Shanghai, was investigated with an integrated approach. Production-based raw material input, city-wide waste output and carbon emissions were compiled for the period 1995–2020, by computing hundreds of products and by-products. Decoupling of these resource and environmental flows from economic development was assessed, and the socio-economic and technical drivers were decomposed. The research demonstrated a hypothesis that flows of primary resources, waste, and carbon emissions displayed a certain level of synchronicity in the past decades. An order effect was seen with waste indicators usually performing better than carbon indicators, and carbon indicators are better than resource indicators in terms of material/environmental intensity and decoupling. There might be a resource leverage leading to the synchronicity of environmental emissions. Improvement in resource efficiency was decomposed as the most significant driver to urban metabolism, bringing about >33 % of resource reduction, 32 % of carbon mitigation, and 30 % of waste diminution from the 2010 values. A greater extent in emission reduction than resource use was attributed to the decrease of fossil fuels share in total resource use and carbon intensity per energy consumption. Continuous increase in post-use waste flows caused a rebound of waste indicators in the recent five-year period (2016–2020) and broke up the synchronicity. This potentially foresees the shift of material metabolism from production to consumption side in major cities in China and calls for reforms of environmental policies.

Longitudinal effects of school policies on children's eating behaviors and weight status: findings from the childhood obesity study in China megacities.

To examine longitudinal effects of school policies on children's weight status and eating behaviors, and study how these effects may vary by children's age, sex, and baseline weight status in China. Data were collected in 2015, 2016, and 2017 in an open cohort of 3298 children aged 6-17, their parents, and schools in five large cities across China (Beijing, Shanghai, Xi'an, Nanjing, and Chengdu). Children's weight, height, and waist circumference were measured, and their eating behaviors were self-reported. The 1691 children with such repeated measures in ≥ two waves were included in longitudinal data analysis with mixed effects models, testing the associations. Having school vicinity food stall policy was associated with less frequent consumption of fast food (β = -0.14, p < 0.01) and snack (β = -0.84, p < 0.01). More significant associations were found between school policies and unhealthy eating behaviors for girls and children aged 6-11 than their counterparts. Among children without overweight or central obesity at baseline, having school cafeteria food policy was associated with lower risks for overweight and obesity (OR = 0.33, 95% CI: 0.17-0.63) and central obesity (OR = 0.47, 95% CI: 0.26-0.85). This existed for girls, but not for boys. School vicinity food stall policy was associated with lower BMI (β = -0.20, 95% CI: -0.37, -0.03) among all children and in girls (β = -0.28, 95% CI: -0.50, -0.05) without overweight at baseline. School policies could reduce children's unhealthy eating behaviors and obesity risk in megacities in China. Children's age, sex, and baseline weight status modify the effects. School policies are important to fight the growing childhood obesity epidemic.

Coupling Efficiency Assessment of Food–Energy–Water (FEW) Nexus Based on Urban Resource Consumption towards Economic Development: The Case of Shenzhen Megacity, China

The population aggregation and economic development caused by urbanization significantly influence the efficiency of urban resource consumption. However, the coupling interactions between crucial resource consumptions such as food, energy and water (FEW) and urbanization processes within highly urbanized areas has not been well-studied. In this study, we constructed an assessment framework for the coupling efficiency measurement of FEW resource consumptions in 10 administrative districts across Shenzhen megacity during 2012–2020, based on the data envelopment analysis (DEA). This study demonstrated that, from the perspective of the FEW nexus, increasing efficiencies in the energy consumption of most districts improved the municipal FEW efficiency, while more than half of the districts did not achieve water resource efficiencies throughout the period. Concerning regional economic development, 80% of the districts improved coupling FEW efficiencies by 2020, the average values of which were higher for Yantian, Nanshan, Luohu and Dapeng, and lower for Baoan, Longgang and Guangming, with a downtrend only being observed in Guangming. Overall, the value of the coupling FEW efficiency of Shenzhen megacity rose by 35% from 2012 to 2020. Correlation analysis showed that synergistic effects of efficient resource consumption occurred in most districts, and economic urbanization was the main driving factor of regional FEW efficiencies within Shenzhen megacity. This study provides instructive insights into the status of urban resource consumption and suggests that the coordination of FEW management should be further improved by fiscal intervention to maintain economic development with the limited resources available, which would have valuable implications for synergistic FEW governance in megacities in China and elsewhere.

The dominant role of aerosol-cloud interactions in aerosol-boundary layer feedback: Case studies in three megacities in China

Interactions between aerosols and meteorology have received increasing attention in recent decades. Through interactions with radiation, aerosols involve in thermodynamic processes and cause cloud adjustment, referred to as the direct and semi-direct effects respectively. They also involve in cloud microphysical processes by severing as cloud condensation nuclei or ice nuclei, referred to as indirect effect. Aerosol direct effect is found to potentially exacerbate air quality by stabilizing the planetary boundary layer (PBL). However, their impacts through the interaction with clouds, including semi-direct and indirect effect remain unclear. In this study, we conducted model simulations to evaluate the direct, semi-direct and indirect effects of aerosols in PBL structure and surface PM2.5 concentration during three heavy haze events under overcast conditions. Overall, the aerosol-PBL feedback results in a 22%–36% decrease of PBL height and 5%–28% increase of PM2.5 concentration. The indirect effect always has the largest impact on PBL and PM2.5 pollution, accounting for 59%–84% of the changes. The semi-direct effect is the weakest on average, although it can exceed the direct effect at certain times and locations. Black carbon aerosols play the vital role in both the direct and semi-direct effects. Our findings promote the understanding of heavy haze formation, and highlight the dominant role of aerosol-cloud interaction in the feedback process of aerosols to PBL structure and air quality.