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The map of radiative cooling potential shows that the radiative cooling power can reach up to 100 W/m2 for its application in different climatic zones. However, the effect of building deployment on the city-scale application of radiative cooling is generally ignored in majority of existing studies, which overestimates the cooling benefit. This paper investigates the cooling benefit of implementing radiative cooling on a city-scale by considering building deployment. To determine the effect of building deployment on the radiative cooling potential, the city of Xi'an in China is modeled using COMSOL and verified with real weather data. Then, the thermal response of buildings with radiative cooling envelopes is discussed in detail. Finally, carbon emission reduction is derived at the city-scale by applying radiative cooling considering building deployment. The results show that the estimated radiative cooling power is approximately decreased by 14.7% for the ideal broadband surface and 47.1% for the ideal selective surface on the selected day by considering building deployment on a city-scale. Furthermore, carbon emission reductions of 0.52 gCO 2 /(m2⋅h) and 0.16 gCO 2 /(m2⋅h) can be achieved from the roof and walls on the selected day by applying radiative cooling material on both the roof and walls. This study can provide guiding significance for the large-scale application of radiative cooling in cities. [ABSTRACT FROM AUTHOR]

• Spatial distribution prediction of pollutants based on machine learning. • A new approach to planning urban ventilation corridors. • Cleanliness assessment of the air at the compensation spaces should be made mandatory. • Urban ventilation corridors worsen air quality in the central city. Urban ventilation corridors are effective in improving urban air quality and alleviating heat island problems, and are widely used in cities around the world. This paper studies typical smog-polluted cities in China to examine whether urban ventilation corridors will worsen air pollution in cities and then proposes countermeasures. First, this paper identifies compensation spaces outside the central urban area of Xi'an and then analyses the prevailing wind direction in these compensation spaces. Based on these findings, this paper identifies potential cold air passages and assesses the air cleanliness in these compensation spaces according to the spatial distributions of PM 2.5 and PM 10. The study finds that four compensation spaces are found outside the central urban area of Xi'an and seven potential cold air passages, including six expressways and one railway, and the PM 10 and PM 2.5 concentrations in three of the four compensation spaces are higher than those in the central urban area. From the beginning (located in the compensation space) to the end (located in the action space) of the cold air passages P1 and P2, PM 2.5 decreased by 11.88% and 11.82%, and PM 10 decreased by 9.40% and 9.76%. This study discovers that if the urban compensation spaces are located in areas with high concentrations of pollutants, the polluted cold air will be introduced to the central urban area along the cold air passages due to the prevailing wind. Unlike previous studies which concluded that urban ventilation corridors improve air quality in central urban areas, this study demonstrates that urban ventilation corridors are at risk of exacerbating air pollution in central urban areas. Therefore, when planning urban ventilation corridors, a city should make an assessment of the air cleanliness of the compensation spaces mandatory to avoid worsening air pollution in the central urban area and creating an unsustainable climate environment due to the planning of urban ventilation corridors, which may further lead to economic losses and threats to public health. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eco-environment assessment of 3 756 urban residential quarters in Xi'an, China. • Factors affecting the ecological environment of residential quarters have been detected. • Specific reference construction values for the eco-environment of residential quarters have been proposed. Residential quarters are a critical component of urban areas, which significantly affects people's health and quality of life. In recent decades, the high-density and crowded residential quarters have become the mainstream organizational model of construction in China, because of the rapid and massive urbanization in many cities. This results in the contradiction between the eco-environment needs and the accommodation needs. Therefore, a systematic evaluation of the eco-environment in residential quarters is urgently needed to address the drawbacks of current residential quarters' planning and design. This paper aims to explore ways to improve the eco-environment with residential quarters from the perspective of China. We first used the Remote Sensing Ecological Index (RSEI) to evaluate the eco-environmental quality of 3, 756 residential quarters in the main urban areas of Xi 'an, China. Then, we quantitatively analyzed the landscape patterns of the impervious surfaces in these residential quarters. Finally, we characterized the impacts of residential quarters layout on the ecological environment by using the vegetation coverage (FVC), the normalized difference bare soil index (NDBSI), building density (BD), the residential density (RD), and the population density (PD) as main factors. The results are as follows: (1) Only 20.5 % of residential quarters with good eco-environments were distributed between the Second and Third Ring Road, indicating the need for improvement in creating livable eco-environments. (2) The shape of the impervious surface of excellent ecological quarters is complex and broken, the average patch area is smaller, and the degree of aggregation and combination of patches is lower compared to residential quarters with poor ecological quality. Therefore, it is recommended to reduce the connectivity of the impervious surface to improve the eco-environment of residential quarters. (3) Among the factors affecting RSEI of residential quarters, FVC, and NDBSI contribute more than other factors. For the construction of excellent eco-environments in residential quarters, we suggest that vegetation coverage should be no less than 0.4, the impervious surface coverage should be no more than 0.53, the building density should be between 0.28 ∼ 0.35, residential density should be no more than 0.22, and the population density of residential quarter should be under 0.29. Overall, for open and low-density residential quarters, the living environment can be improved by enriching vegetation and reducing impervious surfaces, while compact, high-density residential quarters can create a livable eco-environment by optimizing the impervious surface landscape patterns. [ABSTRACT FROM AUTHOR]

[Display omitted] • The failure mode of metro tunnel crossing the edge of land subsidence area is revealed. • The influence of land subsidence on the structural mechanical response are studied. • The damage position and affected range of metro tunnel under the influence of land subsidence are discovered. • The countermeasures are discussed according to different affected positions. Land subsidence is a prominent engineering geological problem faced by many cities in the world and poses a serious threat to urban infrastructures. Xi'an is one of the cities in China that has suffered the most serious land subsidence disasters and has thus faced the challenges in its ongoing metro construction. To solve this problem, in this paper we carried out a model test and numerical simulation of metro tunnel that crosses a land subsidence area and analyzed the mechanical response of the tunnel and the deformation and failure characteristics of the lining. The results show that the tunnel exhibits downward flexural deformation in the middle, slight warpage on both ends in the longitudinal direction, and local torsion in the horizontal direction in the presence of land subsidence, the maximum deformation of the ground surface is about 80% of the tunnel deformation. Furthermore, the vault and inverted arch are in opposite tension–compression states, and the lining stress decreases inside the subsidence area but increases outside it. When the actual subsidence reaches 225 cm, the metro tunnel crossing the edge of the land subsidence area has failed. We find that the deformation and failure of metro tunnel crossing land subsidence area is a combination mode of flexural tension–compression and local torsion, which affects 2.5 times the length of the intersection between the tunnel and the subsidence area. Also, some countermeasures and suggestions are proposed to deal with the adverse impacts of land subsidence on metro tunnels. [ABSTRACT FROM AUTHOR]

To reduce the vulnerability of urban areas facing high temperatures, it is useful to develop methods to obtain the urban heat island (UHI) intensity. However, it is hard to equip all cities with extensive measurement networks and alternative UHI diagnostic methods are needed. Accordingly, in this paper we evaluate and revise the diagnostic equation designed by Theeuwes et al. (2017) and analyze its application for Xi'an (China), based on long-term summer meteorology data. The evaluation of the default diagnostic equation shows that limited accuracy for Xi'an is caused by the sum of morphological parameters being used outside the original range of calibration. Subsequently, we propose an extended equation, which adds the building fraction to express the morphology of additional spatial categories. This new equation is calibrated against a 3-year dataset and independently validated with data from another year. In addition, a class prediction with three spatial categories is proposed, and verified by independent data of 20 stations in Xi'an in 2018, which enables this formula to be applied in more cities. Altogether, the extended diagnostic equation is an effective method to evaluate the daily maximum UHI intensity (UHI max) on neighborhood-scale, which can be generalized for a whole city area and presents internal intensity differences with multi-points. Image 1 • A diagnostic equation for the maximum urban heat island is applied in Xi'an (China). • Building fraction is added to the diagnostic equation to represent morphology. • Sky-view factor and vegetation fraction are used for spatial categorization. • The extended equation is an effective method for UHI max evaluation. [ABSTRACT FROM AUTHOR]

Highlights • The increases of commuting CO 2 emissions are several times larger than the urban size, population, and economics' developments. • Metro services reducing commuting CO 2 emissions near the metro stations is not statistically significant, possibly because the proportions of car users near the metro stations are similar to the two cities' average levels, which is caused by their higher household income and the longer travel time using the metro. • In Beijing, there are the smallest commuting CO 2 emissions in the outer suburbs due to job-housing balances, short distance and large percentage of non-motorized mode uses while the largest commuting CO 2 emissions in the inner sprawl suburbs due to car trips with long distance. Abstract To understand the changing relationships between commuting CO 2 emissions (CCE), travel behavior and urban forms, this paper provides a comparative study between the typical Chinese cities of Beijing (more developed) and Xi'an (rapidly developing). Further, the effects of metro services on reducing CCE were explored, and comparative analysis on CCE between the inner sprawling suburbs and outer suburbs was conducted. It was found that: (i) the increases in CCE are several times larger than the increases in urban size, population, and economic developments; (ii) metro services reducing CCE near metro stations is not statistically significant, maybe because the proportions of car users near the metro stations are similar to the two cities' average levels, which is caused by their higher household income and the longer travel time using the metro; (iii) in Beijing, there are smallest CCE in the outer suburbs due to job-housing balances, short distance and large percentage of non-motorized mode uses while largest CCE in the inner sprawl suburbs due to car trips with long distance. These findings indicate that to cope with the rapidly increasing CCE, more attention should be paid to developing strong industry and real-estate simultaneously; the improvement in the feeder bus and public bicycle systems should also be reinforced to reduce the total travel time of metro users; and satellite cities with job-housing balance are greatly needed. The implications will benefit efforts to reduce CCE and mitigate global climate change, and they also provide empirical evidence and reference values for other global cities. [ABSTRACT FROM AUTHOR]