Global synergy of carbon and pollution emissions among countries with different income levels and development stages.

The world was drift away on the sustainable development goals (SDGs), whatever global countries claimed fighting for. It's thus essential to illustrate the status of development and environmental quality simultaneously. Resource consumption and energy consumption as the basic needs in supporting human societal development, are commonly used, because they come from the same source and are most directly observed in the open air. We thus examined nexus of carbon and pollution emissions, which also directly indicate residents' livelihood and lifestyle. The possibility of the nexus shifts among income levels with population stack analysis was further investigated. Our findings indicate that the diverse nexus is strongly correlated with development levels, with urban areas being the primary contributor to high carbon and/or pollution emissions despite occupying only 0.5% of global territory. We conclude that expecting leapfrog stages of the nexus is unrealistic, as cross-income-level change requires approximately 80% of the population to significant change its livelihood and lifestyle. Therefore, we recommend setting science-based targets for decoupling carbon and pollution emissions from development are necessary, but should be adapted and tailored to each country's local practice.

High-resolution emission inventory of biogenic volatile organic compounds for rapidly urbanizing areas: A case of Shenzhen megacity, China.

The effects of volatile organic compounds on urban air quality and the ozone have been widely acknowledged, and the contributions of relevant biogenic sources are currently receiving rising attentions. However, inventories of biogenic volatile organic compounds (BVOCs) are in fact limited for the environmental management of megacities. In this study, we provided an estimation of BVOC emissions and their spatial characteristics in a typical urbanized area, Shenzhen megacity, China, based on an in-depth vegetation investigation and using remote sensing data. The total BVOC emission in Shenzhen in 2019 was estimated to be 3.84 × 109 g C, of which isoprene contributed to about 24.4%, monoterpenes about 44.4%, sesquiterpenes about 1.9%, and other VOCs (OVOCs) about 29.3%. Metropolitan BVOC emissions exhibited a seasonal pattern with a peak in July and a decline in January. They were mainly derived from the less built-up areas (88.9% of BVOC emissions). Estimated BVOCs comprised around 5.2% of the total municipal VOC emissions in 2019. This percentage may increase as more green spaces emerge and anthropogenic emissions decrease in built-up areas. Furthermore, synergistic effects existed between BVOC emissions and relevant vegetation-based ecosystem services (e.g., air purification, carbon fixation). Greening during urban sprawl should be based on a trade-off between BVOC emissions and ecosystem benefits of urban green spaces. The results suggested that urban greening in Shenzhen, and like other cities as well, need to account for BVOC contributions to ozone. Meanwhile, greening cites should adopt proactive environmental management by using plant species with low BVOC emissions to maintain urban ecosystem services while avoid further degradation to ozone pollution.

Interactions among spatial configuration aspects of urban tree canopy significantly affect its cooling effects.

Increasing urban tree canopy (UTC) has been widely recognized as an effective means for urban heat mitigation and adaptation. While numerous studies have shown that both percent cover of UTC and its spatial configuration can significantly affect urban temperature, the pathways governing these relationships are largely unexplored. Here we present a cross-city comparison aiming to fill this gap by explicitly quantifying the pathways on which percent cover of UTC and its spatial configuration affect land surface temperature (LST) using structural equation modeling (SEM), based on UTC mapped from high resolution imagery and LST derived from Landsat thermal bands. We found: 1) Although both the direct and indirect pathways significantly affected LST regardless of scales and cities, the direct pathway played a more important role in affecting LST in Baltimore, Beijing, and Shenzhen. In contrast, an opposite result was found in Sacramento, likely due to the effects of buildings and their interactions with UTC. 2) Similarly, the direct pathway of mean patch size (MPS) and mean shape index (MSI) played a more important role in affecting LST than their indirect effects via altering edge density (ED). Our results highlighted the necessity for discomposing the effects of different spatial configuration variables on LST. Understanding the pathways through which UTC affects LST can provide insights into urban heat mitigation and adaptation.

Beyond city expansion: multi-scale environmental impacts of urban megaregion formation in China.

Environmental degradation caused by rapid urbanization is a pressing global issue. However, little is known about how urban changes operate and affect environments across multiple scales. Focusing on China, we found urbanization was indeed massive from 2000 to 2015, but it was also very uneven, exhibiting high internal city dynamics. Urban areas in China as a whole became less green, warmer, and had exacerbated PM2.5 pollution. However, environmental impacts differed in newly developed versus older areas of cities. Adverse impacts were prominent in newly urbanized areas, while old urban areas generally showed improved environmental quality. In addition, regional environmental issues are emerging as cities expand, connect and interact to form urban megaregions. To turn urbanization into an opportunity for, rather than an obstacle to, sustainable development, we must move beyond documenting urban expansion to understand the environmental consequences of both internal city dynamics and the formation of urban megaregions.

Transformation of China's urbanization and eco-environment dynamics: an insight with location-based population-weighted indicators.

Within a short period, rapid urbanization has reshaped China's eco-environment, especially at the beginning of the new century. Many studies have focused on the changes in certain physical indicators of eco-environments; however, these indicators cannot directly explain or only slightly consider the eco-environmental benefits of urban residents. Therefore, we analysed location-based population-weighted eco-environmental changes with indicators of the vegetation index and fine particulate matter (PM2.5) concentration at each pixel in China's prefectures and combined the changes with urban expansion to provide an expanded understanding of the transformation of China's urbanization and its eco-environmental dynamics. We discovered that China's urban areas expanded by 38,350 km2 from 2000 to 2015 with an increase in the population-weighted vegetation and PM2.5 concentration, but the changes varied among different periods. From 2005 to 2010, urban areas expanded by 20,970 km2 with an increase in the population-weighted vegetation and PM2.5 concentration. The period from 2000 to 2005 was a key transforming period that experienced an urban expansion of 9081 km2 with a decrease in the population-weighted vegetation and an increase in the population-weighted PM2.5 concentration. An urban expansion of 8299 km2 with an increase in the population-weighted vegetation and a decrease of the population-weighted PM2.5 concentration occurred from 2010 to 2015. The results of this research indicate that China's urbanization and environmental changes have facilitated eco-environmental improvements.

A review of current air quality indexes and improvements under the multi-contaminant air pollution exposure.

The air quality is one of the major concerns in the urban environment due to the rapid changes in pollutant emissions driven by complex and intensive human activities. Therefore, quantification of the urban air quality has become an essential need for both urban residents and authorities to quickly assess air quality conditions. To reach this aim, the air quality index (AQI) is the primary way to better understand the urban air quality. However, the varied AQIs in different countries are difficult to directly compare due to the varied calculation methods. Thus, this research presents an updated review of the major AQIs worldwide by dividing them into two categories: single- and multi-contaminant-oriented AQIs. Single-contaminant-oriented AQIs are based on the maximum value of individual pollutants and are applied in most countries with location-dependent standards, such as the United States, China, the United Kingdom and New South Wales, Australia. However, these may greatly underestimate the impact of multiple contaminants, be difficult to dynamically update or to be compared internationally. Moreover, multi-contaminant-oriented AQIs are available in the literature, which consider the combined effects of exposure to multiple contaminants. Among these AQIs, arithmetic pollutant aggregation simply integrates pollutants in a linear or nonlinear way, and weighted pollutant aggregation further assigns varied weights from different perspectives. Combining the advantages and disadvantages of the existing AQIs, the general air quality health index (GAQHI) is proposed as a pollutant-aggregated, local health-based AQI paradigm suitable for the present complex multi-contaminant situation. It provides a direction for the construction of a more accurate, consistent and comparable AQI system and can help both researchers and governments improve human well-being and achieve sustainable development.

Factors responsible for forest and water bird distributions in rivers and lakes along an urban gradient in Beijing.

Urban rivers and lakes, in combination with nearby green spaces, provide important habitat for urban birds, but few urban studies have focused on forest and water birds simultaneously along an urban intensity gradient. In this study, we randomly chose 39 rivers and lakes along an urban gradient of Beijing to examine bird community parameters in relation to aquatic and terrestrial habitat conditions, aquatic life data, and water quality data. We selected models with the AICc (corrected Akaike information criterion) method, bivariate linear or generalized linear regressions, and structural equation modeling to determine distribution patterns of avian communities along an urban gradient and bird-environment relationships. We found that both forest and water bird species and individuals peaked at intermediate urbanization intensities, especially for abundance of both forest and water bird and water bird species richness and abundance. We suggest that the differences in the strength of response to urbanization and the similarities in the gradient distribution pattern between forest and water birds should receive more attention in future urbanization gradient studies. Significant correlation ship between species richness of resident water birds, fish foragers, and insectivore-frugivores, abundance of insectivores, insectivore-frugivores (negative), and granivores (positive) and impervious surface proportion within 1-km radius buffer of sampled sites became more evident after coverage of artificial surfaces exceeded a 50% threshold. Regressions showed that distance from the urban center, number of islands in waterbody, and proportion of gross or unarmored shoreline length were significantly and positively related to species richness and abundance of both forest and water birds. The availability of unarmored shoreline is a critical pathway through which urbanization detrimentally impacts avian diversity. Our results demonstrate how the urban intensity gradient affects the relative availability of food resources and habitat, which could provide practical applications for urban landscape planning and avian biodiversity conservation in urban areas.

China's Complex Urban Air Pollution: An Improved Understanding with Ground Operational Measurements.

Complex urban air quality has long been assessed by a single (or major) contaminant, for example, fine particulate matter (PM2.5), but scant attention has been given to multicontaminant air pollution, especially in countries with severe air pollution, for example, China. We thus proposed an improved method for quantifying both single- and multicontaminant air pollution. Our approach uses China's major cities as an example because they have an operational national urban air quality monitoring network. We found that our proposed method could remove the duplicated consideration under both single- and multicontaminant conditions, thus proving to be an improved and more accurate way to understand complex urban air pollution conditions. Our method involved monitoring 3 contaminants (PM2.5, PM10, and SO2 ) in cities in Shanxi, Shandong, Henan, and Hebei Provinces and 2 contaminants (PM2.5 and PM10) in the cities between the Yellow River and the Yangtze River, and these pollutants were the major contributors to multicontaminant air pollution. We argue that both the research community and the government should pay increased attention to multicontaminant air pollution beyond the current single major pollutant-based air pollution method when building a sustainable city. Integr Environ Assess Manag 2020;16:306-313. © 2020 SETAC.

Breathing the same air? Socioeconomic disparities in PM2.5 exposure and the potential benefits from air filtration.

Air pollution caused by particulate matter <2.5 µm in diameter (PM2.5) imposes a severe health burden to people worldwide. Across the globe, and even within cities, the health burden of air pollution is not equally shared by citizens. Despite being the region suffering from the most severe air pollution, studies examining the inequity of the burdens of air pollution in Asia are limited. We aim to fill in this gap by analyzing the relationship between PM2.5 pollution and residents' socioeconomic characteristics in Beijing, the icon city for PM2.5 pollution. Our results show that household income and education were negatively correlated with ambient air quality (r = -0.62; p < 0.05 and r = -0.73; p < 0.01 respectively) in 2014. We found in Beijing air quality is worse where residents have less income and lower education rates and are less capable to protect themselves from the potential health risk. To counter the effects of air pollution in Beijing, air filtration has been shown to be an effective means to reduce, at least, indoor PM2.5 levels. We illustrate through a simple scenario analysis that air filtration can reduce exposure (26-79%) to a similar extent as the structural mitigation programs (e.g. closing coal factories) achieved in recent years (53%). We argue government intervention is needed to convey the benefit of air filtration to the socioeconomically disadvantaged groups.

Urbanization strategy and environmental changes: An insight with relationship between population change and fine particulate pollution.

Fine particulate (PM2.5) pollution, along with the rapid urbanization process, has been given much attention in China during the recent decades. However, the relationships between urban population dynamics and PM2.5 changes have not been well examined. We therefore analyzed their relationship using full-coverage remotely sensed PM2.5 and population density data. The results showed that 1) both population density and PM2.5 concentration increased rapidly from 2000 to 2014, especially in East and Central China, as well as China's high population density urban areas and the major cities; 2) A total of 723 million people was exposed to PM2.5 pollution in 2014, an increase of 105 million from 2000; 3) most of the urban areas exhibited population density increase/decrease with PM2.5 concentration increase, while a total of 42% of China's territory, mainly in East and Central China's rural areas were found to have population decrease but PM2.5 concentration increase. We hope the results in this work can serve as an example to other countries in designing their urbanization strategy by paying more attention to environmental degeneration accompanying rapid development. CAPSULE ABSTRACT: Most of urban areas were observed to have population density increase/decrease along with PM2.5 concentration increase.

Multicontaminant air pollution in Chinese cities.

OBJECTIVE: To investigate multicontaminant air pollution in Chinese cities, to quantify the urban population affected and to explore the relationship between air pollution and urban population size. METHODS: We obtained data for 155 cities with 276 million inhabitants for 2014 from China's air quality monitoring network on concentrations of fine particulate matter measuring under 2.5 µm (PM2.5), coarse particulate matter measuring 2.5 to 10 µm (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2) and ozone (O3). Concentrations were considered as high, if they exceeded World Health Organization (WHO) guideline limits. FINDINGS: Overall, 51% (142 million) of the study population was exposed to mean annual multicontaminant concentrations above WHO limits - east China and the megacities were worst affected. High daily levels of four-contaminant mixtures of PM2.5, PM10, SO2 and O3 and PM2.5, PM10, SO2 and NO2 occurred on up to 110 days in 2014 in many cities, mainly in Shandong and Hebei Provinces. High daily levels of PM2.5, PM10 and SO2 occurred on over 146 days in 110 cities, mainly in east and central China. High daily levels of mixtures of PM2.5 and PM10, PM2.5 and SO2, and PM10 and SO2 occurred on over 146 days in 145 cities, mainly in east China. Surprisingly, multicontaminant air pollution was less frequent in cities with populations over 10 million than in smaller cities. CONCLUSION: Multicontaminant air pollution was common in Chinese cities. A shift from single-contaminant to multicontaminant evaluations of the health effects of air pollution is needed. China should implement protective measures during future urbanization.

The rapid but "invisible" changes in urban greenspace: A comparative study of nine Chinese cities.

Quantifying the spatial pattern and change of urban greenspace is a prerequisite to understanding the myriad ecosystem services provided by urban greenspace. Previous studies have largely focused on loss of greenspace due to urban expansion, using medium resolution imagery. This paper presents a comparison study on the spatiotemporal patterns of urban greenspace in nine major cities in China, using 2.5m resolution ALOS and SPOT image data collected in 2005 and 2010, respectively. The changes in urban greenspace were further compared with those based on the commonly used 30m Landsat TM data. The results show: 1) Urban greenspace was highly fragmented and heterogeneous, characterized by a mix of a large number of small-sized patches (smaller than 0.1ha) with relatively few dispersed large patches in nine cities. 2) In contrast to findings from previous research that greenspace in inner cities tends to remain largely unchanged, urban greenspace in all nine cities was highly dynamic, experiencing both gain and loss, with net change ranging from 0.51% to 11.26% over five years. Most of the changes in urban greenspace, however, tended to occur as small patches, and could only be revealed by high spatial resolution imagery. 3) Spatial patterns of greenspace varied greatly across cities in terms of patch size, patch and edge density, and shape. Urban greenspace became increasingly fragmented and complex in the southern cities, but the opposite in the northern cities. The high turnover dynamics of urban greenspace in cities proper provide opportunities for better design and planning to achieve urban sustainability, but also call for better protection of small-sized urban greenspaces in Chinese cities.