Megacity In China Research Articles

Spatial distribution, risk estimation and source apportionment of potentially toxic metal(loid)s in resuspended megacity street dust.

The levels of potentially toxic metal(loid)s (PTMs) As, Cu, Co, Cr, Hg, Mn, Ni, Pb, and Zn in resuspended street dust (<100μm particles) from a megacity in north China were determined. The sources of PTMs in resuspended street dust were analyzed using multivariate statistical analysis and positive matrix factorization methods that combined the spatial distributions of PTMs. Average levels of Zn, As, Pb, Cu, Co, and Hg exceeded those found in local soil samples, while those of Cr, Mn, and Ni were less than their background levels found in local soil. The overall contamination of PTMs in resuspended street dust was characterized as moderately contaminated and as uncontaminated to moderately contaminated. The ecological risk associated with Hg was very high, while the ecological risks associated with Cu, Co, Cr, Mn, Ni, Pb, and Zn were low. The overall ecological risk of PTMs was defined as high, driven by Hg. The non-carcinogenic risks of PTMs to inhabitants fell within safety limits, and the carcinogenic risks of As, Co, Cr, and Ni were below receivable values. A comprehensive analysis of PTMs sources revealed that Co, Zn, Cu, and Pb were principally associated with traffic emissions, which accounted for about 38.3% of these PTMs' contents. Mn, Ni, and Cr were mainly generated by natural source, which contributed to about 41.5% of these PTMs' concentrations. Hg and As were primarily derived from coal-related industrial source, which accounted for 77.9% of Hg and 62.9% of As in resuspended street dust. This study demonstrates that coal-related industrial discharges and traffic emissions are the main anthropogenic sources of PTMs contamination in resuspended street dust in the study area.

Polyethylene scaffold net and synthetic grass fragmentation: a source of microplastics in the atmosphere?

Microplastics (MPs) implications in the atmosphere are of current global concern. Currently, there is a growing interest regarding source appointment, fate, level of toxicity, and exposure intensity of ambient air MPs. Recent data suggest that polyethylene (PE) dominates ambient MPs in China's megacities. Albeit understanding of PE sources is limited and restricted to typical sources polluting terrestrial and marine environments. However, the air is a distinct environmental component and may have some separate pollution sources as well as the relative contribution of different sources could also contrast in different environments. Urbanization and fast construction activity resulting from increased economic growth in these places might be a potential source of ambient PE. Recently, the use of scaffold netting on construction sites and synthetic grass as land covering sheets has been on the rise. Generally, these PE items are often inferior and composed of recycled material, making them more prone to degradation. Also, because these items were continually exposed to open air, there is a considerable risk of fragmentation and atmospheric mixing. Therefore, unchecked and excessive usage of these materials can be risky. Here, PE's physical and chemical characteristics, transport and health risks in urban air are discussed here.

Urban Heat Islands Significantly Reduced by COVID‐19 Lockdown

AbstractThe significant reduction in human activities during COVID‐19 lockdown is anticipated to substantially influence urban climates, especially urban heat islands (UHIs). However, the UHI variations during lockdown periods remain to be quantified. Based on the MODIS daily land surface temperature and the in‐situ surface air temperature observations, we reveal a substantial decline in both surface and canopy UHIs over 300‐plus megacities in China during lockdown periods compared with reference periods. The surface UHI intensity (UHII) is reduced by 0.25 (one S.D. = 0.22) K in the daytime and by 0.23 (0.20) K at night during lockdown periods. The reductions in canopy UHII reach 0.42 (one S.D. = 0.26) K in the daytime and 0.39 (0.29) K at night. These reductions are mainly due to the near‐unprecedented drop in human activities induced by strict lockdown measures. Our results provide an improved understanding of the urban climate variations during the global pandemic.

PM2.5-bound phthalates and phthalate substitutes in a megacity of southern China: spatioseasonal variations, source apportionment, and risk assessment.

Plasticizers are ubiquitous pollutants in the environment, whereas few efforts have been made to elucidate their emission sources in the atmosphere. In this research, the spatioseasonal variations and sources of particle-bound (PM2.5) phthalates (PAEs) and their substitutes (APs) at residential sites in seven districts and at four potential point-source sites across a megacity in South China were revealed. The total concentrations of PAEs ranging from 10.7 to 528ng/m3 were substantially higher than those of APs (1.45.58.5ng/m3). Significant spatial variations in the concentrations of the pollutants were observed, which were generally higher at the sites with intensive industrial activities and the point-source sites. Most atmospheric plasticizer levels peaked in summer, probably due to the temperature-promoted volatilization. Seven sources of plasticizers were identified by the positive matrix factorization (PMF) model. The sources in less industrialized districts are mainly associated with domestic and commercial emissions and with industry in the industrialized districts. Specifically, plastics and personal care products together contributed 60% of the plasticizers in the atmosphere of this city, followed by solvents and polyester industry sources. The incremental lifetime cancer risk of inhalation exposure to bis(2-ethylhexyl) phthalate in the study city is below the acceptable level. Relatively higher risks were found for residents living around sites with intensive industrial activities and around wastewater treatment plant.

Secondary organic aerosol formation and aging from ambient air in an oxidation flow reactor during wintertime in Beijing, China

Secondary organic aerosols (SOA) constitute a large fraction of atmospheric aerosols, yet our knowledge of the formation and aging processes of SOA in megacities of China is still limited. In this work, the formation and aging processes of SOA in winter in Beijing was investigated using a high-resolution aerosol mass spectrometer (AMS) and an oxidation flow reactor (OFR). Our results showed that the OA enhancement from OH aging peaked at ∼3.9 equivalent days with an average enhancement of 0.9 (±0.3) μg m−3. Positive matrix factorization analysis of AMS-OFR data identified three primary OA (POA) and two SOA factors. While the concentrations of POA factors decreased as a function of photochemical age, the two SOA factors showed clear enhancements by 2.5 and 4.3 μg m−3 at ∼3.9 and ∼2.6 days of equivalent photochemical age, respectively. The average contribution of SOA to the total OA was 47% in ambient air and 87% in OFR-oxidized ambient air. The elevated oxygen-to-carbon (O/C) ratio from 0.49 to 0.77–0.82 and the decreased hydrogen-to-carbon (H/C) from 1.37 to ∼1.1 highlighted the formation of more oxidized SOA during photochemical aging in winter in Beijing. The ubiquitous SOA enhancement as a function of OA levels indicated the significant formation potential of SOA in winter, and it varied differently among different episodes. In particular, we observed a maximum SOA enhancement of 38.6 μg m−3 during a biomass burning event. This result demonstrates that photochemical oxidation of ubiquitous biomass burning emissions can be a large source of SOA in winter in North China Plain.

Exploring Built Environment Influence on Taxi Vacant Time in Megacities: A Case Study of Chongqing, China

Driven by the emission peak and carbon neutrality targets, traditional cruising taxis are also under pressure to reduce emissions, and reducing taxi vacant time is an effective way to reduce emissions. This paper aims to examine the influence mechanism of built environment characteristics on vacant time of taxi trips from the supply-side perspective. To do so, the study uses a one week of taxi trajectory data of 2019 provided by a taxi company in Chongqing, a megacity in China. We take the divided square grid cell as the study units, calculate the taxi vacant time of 168 (7 × 24) hourly slots for each grid, and then calculate the built environment indicators of the grids with Point of Interest (POI) and vector road network data. A generalized additive model (GAM) based on panel data is constructed to investigate the influence mechanism of built environment on taxi vacant time. The results show that the time-varying trend of taxi vacant time is opposite to the time-varying trend of taxi trips and is similar to taxi trips in spatial distribution with significant spatial dependence. Taxi vacant time is negatively correlated with taxi trips. POI mixture, the number of enterprises, governmental agencies, and shopping services are negatively correlated with vacant time, while the number of sports and leisure services, hotel services, healthcare services, financial and insurance services, and living services are positively correlated with vacant time. An interesting finding is that metro stations significantly increase the vacant taxi time in the region. Average traffic flow speed, road density, the number of bus stops, catering services, residence communities, and motor vehicle services show strong nonlinear relationships with taxi vacant time, and their influence effects are alternately positive and negative. The study provides useful insights for understanding mechanisms of the role of built environment on taxi vacant time and has important implications for driver searching strategy improvement, taxi management measures development, spatial and temporal scheduling of taxi capacity resources, and urban transportation facilities layout planning.

City profile: Wuhan 2004–2020

As an inland megacity in central China, Wuhan has witnessed a rapid economic revival and comprehensive transformation in the past 16 years. Due to the adaptive urban governance toward national and global changes, Wuhan has shown its strength by leading in regional growth and development. By adopting statistics, data visualization, observations, and surveys, we profiled Wuhan through the perspective of an organic assemblage framework, which shows how political restructuring, pro-growth development strategies, and concerns for livability and crisis mitigation played the key roles in organizing resources for sustainable development in globalization. It also adds insight concerning strong urban governance at the interstices of time, space, and institutions.

A license plate recognition data to estimate and visualise the restriction policy for diesel vehicles on urban air quality: A case study of Shenzhen

Diesel vehicles for road freight are primary contributors to PM2.5 and NOX emissions in numerous cities. Shenzhen, which is a megacity in China, has made efforts to promote the transition to green transport by implementing license plate restrictions. Nevertheless, it is still unclear whether the restrictions have greatly improved urban air quality. An effective framework for accurately estimating and visualising the effect of restriction policy on a large scale is still lacking. Therefore, this study aims to develop a novel method to visualise and evaluate the effect of license plate restriction policy by bridging diesel truck's license plate recognition data to emission inventories. The results reveal that the impact of the peak restriction on air quality was limited if it only affected nonlocal diesel vehicles. While the promotion of eco-friendly vehicles could reduce PM2.5 and NOX emissions. The findings could provide references for other cities or countries to estimate air pollution from diesel vehicles and recognise high emission zones at a large scale and thus create effective policies and initiatives.

Fine Particle pH and its Impact on PM2.5 Control in a Megacity of Central China

Fine particle (PM2.5) acidity greatly affects the formation of secondary aerosol, and the drivers of PM2.5 pH variation are vital in understanding its effects. Moderate PM2.5 acidity was found in Wuhan, a megacity of Central China, wherein 80% of PM2.5 hold pH values ranging from 2–4. Total ammonia (NHx) and sulfate contributed 79.1–93.7% to pH changes in spring and winter, while relative humidity was the largest contributor (33.7–36.3%) in summer and fall. By sensitivity simulations, PM2.5 remained acidic with pH changes less than 0.5 units in spring, summer and fall in foreseeable future even when the concentration varied by two orders of magnitude. While pH changes in winter were three times those in the other seasons, and NHx changes was suggested as the indicator of PM2.5 pH variation in winter. Furthermore, the impact of pH on PM2.5 responses to emissions control was evaluated. The pH has opposite influences on the effect of SO2 and NOx control in reducing PM2.5, the former being more effective at low pH and the latter being more effective at high pH due to ammonium and nitrate gas-particle partitioning. The effect of NHx control on PM2.5 reduction is nonlinearly affected by pH. It is directly effective at low pH, but more ammonia control is required before achieving effectiveness at high pH. For the current particulate pH of 3–4 in Wuhan, both SO2 and NOx control are beneficial for PM2.5 reduction. However, NHx control is less effective before it is reduced by approximately 20%.

Leverage of Resource Efficiency Over Environmental Emissions: Case of a Megacity in China

Leverage of Resource Efficiency Over Environmental Emissions: Case of a Megacity in China

Green Infrastructure and Air Pollution: Evidence from Highways Connecting Two Megacities in China

Green Infrastructure and Air Pollution: Evidence from Highways Connecting Two Megacities in China

Chemical Composition, Sources and Secondary Processes of Aerosols in a Megacity of China

Chemical Composition, Sources and Secondary Processes of Aerosols in a Megacity of China

Optimization of Landscape Ecological Security Patterns and Planning in Low Hilly Areas —A Case Study of Beigong Town, Fengtai District, Beijing City, China

With the continuous expansion of mega-cities in China, the landscape pattern of the original urban-rural area is broken, resulting in serious fragmentation of landscape patches in the fringe area of the urban center and threatening urban ecological security. Therefore, how to consider the needs for construction and development based on securing ecological security patterns is a key consideration for the fringe areas of megacities. The study takes Beigong Town as the research object and uses the MSPA model analysis method to extract nine ecological source sites that are important for ecological network construction. Then, the study constructs a comprehensive ecological resistance surface based on the MCR minimum cumulative resistance model, generates minimum cost paths to simulate regional potential corridors, and constructs the ecological security pattern in Beigong Town. The study further combines the current situation of land use in Beigong Town to optimize the ecological safety pattern and proposes the planning control systems, which provides the basis for the next planning and construction.

Health Impact of Exposure to Paes in Household Dust on Children in Nine Mega-Cities in China: An On-Site Observational Study

Health Impact of Exposure to Paes in Household Dust on Children in Nine Mega-Cities in China: An On-Site Observational Study

Correlating indoor and outdoor temperature and humidity in megacities in China

Since people spend much more time indoors, indoor conditions may be better indicators of personal exposure than outdoor. Several studies have explored the associations between indoor and outdoor temperature, humidity in USA or in tropical regions. Few studies examined these associations in China. In this study, we collected the daily indoor temperature and relative humidity (RH) in 1577 household in four megacities across temperate and subtropical regions in China, from March 2017 to July 2018. We use Pearson correlation analysis to examine their correlations with outdoor. We found that the correlation between indoor and outdoor RH was stronger in Northern China (r=0.76 V.S. r=0.58), while the correlation between indoor and outdoor temperature was stronger in Southern China (r=0.92 V.S. r=0.80). In the winter-spring months, there was no statistically significant linear relationship between indoor and outdoor temperature. However, the correlation between indoor and outdoor RH in high urbanized regions in winter-spring was stronger than that in low urbanized regions (r=0.85 V.S. r=0.70). This may be due to the comment use of air conditioning and ground heating in the high urbanized regions. This study provides insight for assessing the indoor-outdoor environment correlations in China.

Material Stock Accumulation Accelerating with Urbanization and Still Unsaturated When the Rate Reaches 80% in China's Megacities

Material Stock Accumulation Accelerating with Urbanization and Still Unsaturated When the Rate Reaches 80% in China's Megacities

Characterizing Formation Mechanisms of Secondary Aerosols on Black Carbon in a Megacity in South China

Characterizing Formation Mechanisms of Secondary Aerosols on Black Carbon in a Megacity in South China

Quantifying the Relative Contributions of Aqueous Phase and Photochemical Processes to Water-Soluble Organic Carbon Formation in Winter in a Megacity of South China

Quantifying the Relative Contributions of Aqueous Phase and Photochemical Processes to Water-Soluble Organic Carbon Formation in Winter in a Megacity of South China

Aquatic Environmental Fates and Risks of Benzotriazoles, Benzothiazoles, and P-Phenylenediamines in a Catchment Providing Water to a Megacity of China

Aquatic Environmental Fates and Risks of Benzotriazoles, Benzothiazoles, and P-Phenylenediamines in a Catchment Providing Water to a Megacity of China

Accelerated toluene degradation over forests around megacities in southern China

Toluene is a typical anthropogenic pollutant that has profound impacts on air quality, climate change, and human health, but its sources and sinks over forests surrounding megacities remain unclear. The Nanling Mountains (NM) is a large subtropical forest and is adjacent to the Pearl River Delta (PRD) region, a well-known hotspot for toluene emissions in southern China. However, unexpectedly low toluene concentrations (0.16 ± 0.20 ppbv) were observed at a mountaintop site in NM during a typical photochemical period. A backward trajectory analysis categorized air masses received at the site into three groups, namely, air masses from the PRD, those from central China, and from clean areas. The results revealed more abundant toluene and its key oxidation products, for example, benzaldehyde in air masses mixed with urban plumes from the PRD. Furthermore, a more than three times faster degradation rate of toluene was found in this category of air masses, indicating more photochemical consumption in NM under PRD outflow disturbance. Compared to the categorized clean and central China plumes, the simulated OH peak level in the PRD plumes (15.8 ± 2.2 × 106 molecule cm−3) increased by approximately 30% and 55%, respectively, and was significantly higher than the reported values at other background sites worldwide. The degradation of toluene in the PRD plumes was most likely accelerated by increased atmospheric oxidative capacity, which was supported by isoprene ozonolysis reactions. Our results indicate that receptor forests around megacities are not only highly polluted by urban plumes, but also play key roles in environmental safety by accelerating the degradation rate of anthropogenic pollutants.