Urban street canyons formed by high-rise buildings restrict the dispersion of vehicle emissions, which pose severe health risks to the public by aggravating roadside air quality. However, this issue is often overlooked in city planning. This paper reviews the mechanisms controlling vehicle emission dispersion in urban street canyons and the strategies for managing roadside air pollution. Studies have shown that air pollution hotspots are not all attributed to heavy traffic and proper urban design can mitigate air pollution. The key factors include traffic conditions, canyon geometry, weather conditions and chemical reactions. Two categories of mitigation strategies are identified, namely traffic interventions and city planning. Popular traffic interventions for street canyons include low emission zones and congestion charges which can moderately improve roadside air quality. In comparison, city planning in terms of building geometry can significantly promote pollutant dispersion in street canyons. General design guidelines, such as lower canyon aspect ratio, alignment between streets and prevailing winds, non-uniform building heights and ground-level building porosity, may be encompassed in new development. Concurrently, in-street barriers are widely applicable to rectify the poor roadside air quality in existing street canyons. They are broadly classified into porous (e.g. trees and hedges) and solid (e.g. kerbside parked cars, noise fences and viaducts) barriers that utilize their aerodynamic advantages to ease roadside air pollution. Post-evaluations are needed to review these strategies by real-world field experiments and more detailed modelling in the practical perspective.

Urban heat island (UHI), an iconic consequence of anthropogenic activities and climate condition, affects air pollution, energy use, and health. Therefore, better understanding of the temporal dynamics of UHI is required for sustainable urban planning to mitigate air pollution under a changing climate. Here, we present the evolution of UHI intensity (UHIi) and its controlling factors in the Seoul metropolitan area, Korea, over the last 56 years (1962–2017), which has experienced unique compressed economic growth and urban transformation under monsoon climate. The analysis demonstrated an inverted U-shape long-term variation of UHIi with the progress of urban transformation and economic climate which has not been reported in Asian cities before. Meanwhile, short-term variations in UHIi are related to both diurnal temperature range and duration after rainfall event unlike previous studies, and the UHIi was exacerbated by heat waves. Our findings suggest that the UHIi will exhibit different temporal dynamics with future changes in the monsoon climate, and heat waves in the urban area will be reinforced if current rapid urbanization continues without a shift toward sustainable and equitable development. Asian cities that are likely to face the similar urbanization trajectory and the implications are that urban (re)development strategy considers changes in rainfall magnitude and timing due to monsoon system variation under changing climate and plans to mitigate synergy between heat wave and UHI in this area.

Air pollutants emitted from vehicles in street canyons may be reactive, undergoing mixing and chemical processing before escaping into the overlying atmosphere. The deterioration of air quality in street canyons occurs due to combined effects of proximate emission sources, dynamical processes (reduced dispersion) and chemical processes (evolution of reactive primary and formation of secondary pollutants). The coupling between dynamics and chemistry plays a major role in determining street canyon air quality, and numerical model approaches to represent this coupling are reviewed in this article. Dynamical processes can be represented by Computational Fluid Dynamics (CFD) techniques. The choice of CFD approach (mainly the Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) models) depends on the computational cost, the accuracy required and hence the application. Simplified parameterisations of the overall integrated effect of dynamics in street canyons provide capability to handle relatively complex chemistry in practical applications. Chemical processes are represented by a chemical mechanism, which describes mathematically the chemical removal and formation of primary and secondary species. Coupling between these aspects needs to accommodate transport, dispersion and chemical reactions for reactive pollutants, especially fast chemical reactions with time scales comparable to or shorter than those of typical turbulent eddies inside the street canyon. Different approaches to dynamical and chemical coupling have varying strengths, costs and levels of accuracy, which must be considered in their use for provision of reference information concerning urban canopy air pollution to stakeholders considering traffic and urban planning policies.

Following formative work in the 1970s, disappearance in the 1980s, and reemergence in the 1990s, a chronological review shows that the past decade has witnessed increasing interest in the study of urban metabolism. The review finds that there are two related, non-conflicting, schools of urban metabolism: one following Odum describes metabolism in terms of energy equivalents; while the second more broadly expresses a city’s flows of water, materials and nutrients in terms of mass fluxes. Four example applications of urban metabolism studies are discussed: urban sustainability indicators; inputs to urban greenhouse gas emissions calculation; mathematical models of urban metabolism for policy analysis; and as a basis for sustainable urban design. Future directions include fuller integration of social, health and economic indicators into the urban metabolism framework, while tackling the great sustainability challenge of reconstructing cities.

In China, ambient fine particulate matter (PM₂.₅) causes a large health burden and raises specific concerns for policymakers. However, assessments of the health effects associated with air pollution from industrial land layouts remain inadequate. This study established a comprehensive assessment framework to quantify the health and economic impacts of PM₂.₅ exposure at different industrial geographical locations. This framework aims to optimize the spatial distribution of industrial emissions to achieve the lowest public health costs in Changsha, a representative industrial city in China. Health effects were estimated by applying the integrated exposure-response model and a long-range pollution dispersion model (CALPUFF). The value of statistical life (VSL) was used to monetize health outcomes. It was found that implementing an optimal industrial land layout can yield considerable social and financial benefits. Compared with the current industrial space layout, in 2030, the averted contribution by Changsha’s industrial sector to PM₂.₅-related mortality and corresponding economic losses will be 60.8% and 0.69 billion US dollars (USD), respectively. The results of optimization analyses highlighted that population density and emission location are significant factors affecting the health burden. This method can identify the optimal geographical allocation of industrial land with minimal expected health and economic burden. These results will also provide policymakers with a measurable assessment of health risks related to industrial spatial planning and the associated health costs to enhance the effectiveness of efforts to improve air quality.

Rapid urbanization, which is closely related to economic growth, human health, and micro-climate, has resulted in a considerable amount of anthropogenic heat emissions. The lack of estimation data on long-term anthropogenic heat emissions is a great concern in climate and urban flux research. This study estimated the annual average anthropogenic heat fluxes (AHFs) in Beijing–Tianjin–Hebei region in China between 1995 and 2015 on the basis of multisource remote sensing images and ancillary data. Anthropogenic heat emissions from different sources (e.g., industries, buildings, transportation, and human metabolism) were also estimated to analyze the composition of AHFs. The spatiotemporal dynamics of long-term AHFs with high spatial resolution (500 m) were estimated by using a refined AHF model and then analyzed using trend and standard deviation ellipse analyses. Results showed that values in the region increased significantly from 0.15 W· m−2 in 1995 to 1.46 W· m−2 in 2015. Heat emissions from industries, transportation, buildings, and human metabolism accounted for 64.1%, 17.0%, 15.5%, and 3.4% of the total anthropogenic heat emissions, respectively. Industrial energy consumption was the dominant contributor to the anthropogenic heat emissions in the region. During this period, industrial heat emissions presented an unstable variation but showed a growing trend overall. Heat emissions from buildings increased steadily. Spatial distribution was extended with an increasing tendency of the difference between the maximum and the minimum and was generally dominated by the northeast–southwest directional pattern. The spatiotemporal distribution patterns and trends of AHFs could provide vital support on management decision in city planning and environmental monitoring.

Urbanization usually pollutes the environment leading to alterations in key biogeochemical cycles. Therefore, understanding its effects on forest nitrogen (N) saturation is becoming increasingly important for addressing N pollution challenges in urban ecosystems. In this study, we compared soil (N availability, net N mineralization, net nitrification, and δ¹⁵N) and foliar (N concentrations and δ¹⁵N) variables in upstream, midstream and downstream forest stands of Bailongjiang River (BJR; more urbanized) and Wulongjiang River (WJR; less urbanized), the two branches of the Minjiang River Estuary. Total soil N, ammonium, nitrate, net N mineralization and nitrification rates, as well as soil δ¹⁵N were significantly higher in BJR compared with WJR forest stands. While no substantial difference in foliar N concentrations was noted between rivers, foliar δ¹⁵N was on average more than 2.5 times higher in BJR than WJR forest stands. Across the study area, foliar δ¹⁵N was positively related to soil δ¹⁵N, which also had positive linear relationships with soil nitrate concentrations, net N mineralization and net nitrification rates. Moreover, all variables except foliar δ¹⁵N and ammonium concentrations showed decreasing patterns in the order: upstream > midstream > downstream along the BJR forest stands. Soil ammonium and foliar values (N concentrations and δ¹⁵N) revealed clear patterns along the WJR, with the former increasing and the latter decreasing from the upstream to downstream forest stands. Our findings indicate an increase in urbanization-induced N inputs from the WJR to BJR and that forest stands along the BJR especially at the upstream have higher N availability and are shifting rapidly towards N saturation state. These results emphasize the need for effective N pollution control in urban environments through sustainable urban planning.

The cities of today present requirements that are dissimilar to those of the past. There are cities where the industrial and service sectors are in decline, and there are other cities that are just beginning their journey into the technological and industrial sectors. In general, the political and social realms have been restructured in terms of economics, which has resulted in an entirely different shape to the primitive structures of civilization. As people begin to understand the dynamic nature of landscapes, they stop seeing landscapes as a static scene. Sustainable cities must be simultaneously economically viable, socially just, politically well managed and ecologically sustainable to maximize human comfort. The present research suggests a multi-disciplinary approach for attaining a holistic understanding of urban environmental quality and human well-being in relation to sustainable urban development.

This study applies remote sensing technology to assess and examine the spatial and temporal Brightness Temperature (BT) profile in the city of Tel-Aviv, Israel over the last 30 years using Landsat imagery. The location of warmest and coldest zones are constant over the studied period. Distinct diurnal and temporal BT behavior divide the city into four different segments. As an example of future application, we applied mixed regression models with daily random slopes to correlate Landsat BT data with monitored air temperature (Tair) measurements using 14 images for 1989–2014. Our preliminary results show a good model performance with R² = 0.81. Furthermore, based on the model's results, we analyzed the spatial profile of Tair within the study domain for representative days.

Heavy metals in urban soils can compromise human health, especially in urban gardens, where gardeners may ingest contaminated dust or crops. To identify patterns of urban garden metal contamination, we measured concentrations and bioavailability of Pb, As, and Cd in soils associated with twelve community gardens in Los Angeles County, CA. This included sequential extractions to partition metals among exchangeable, reducible, organic, or residual fractions. Proximity to road increased all metal concentrations, suggesting vehicle emissions sources. Reducible Pb increased with neighborhood age, suggesting leaded paint as a likely pollutant source. Exchangeable Cd and As both increased with road proximity. Only cultivated soils showed an increase in exchangeable As with road proximity, potentially due to reducing humic acid interactions while Cd bioavailability was mitigated by organic matter. Understanding the geochemical phases and metal bioavailability allows incorporation of contamination patterns into urban planning.