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• 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]

Abstract Air pollution is widely believed to cause healthy risks and influence nations' economic dimensions. This paper investigates the impact of air pollution on housing prices in China's 286 prefectural-level cities during 2005–2013. To address the endogeneity problem of PM 2.5 concentrations in our regression, we propose an instrument variable strategy based on ventilation coefficient. The estimation results suggest that a 10% increase in PM 2.5 concentrations causes a 2.4% reduction in local housing prices. Air pollution also hinders the progress of urbanization, limits cities' human capital formation and changes people's expectations of housing prices that we interpret as three potential mechanisms behind our main findings. [ABSTRACT FROM AUTHOR]

Abstract: By means of computational fluid dynamic (CFD) simulations, this paper investigated how rural winds transport relatively clean air into high-rise urban areas to dilute airborne pollutants. Two ventilation concepts for indoor environments were applied: the age of air to quantify the time taken by rural young air to reach a given place after it enters an urban area and the air exchange efficiency to evaluate the efficiency of rural winds flushing the entire urban canopy layer. Several square building arrays with street aspect ratios (building height/street width, H/W) ranging from 1.5 to 5.3 and building area densities of 0.25 (medium) or 0.4 (compact) were considered as the approaching wind is parallel to the main street whose length varies from street scales to neighborhood scales (330–510 m to 1.03–1.65 km in full-scale). Results show that considerable young rural air enters windward entries but a major fraction of air is vertically driven out as flowing deeper into such high-rise building arrays. So air exchange efficiencies are less than 50% in street-scale arrays, and smaller in longer (neighborhood-scale) or narrower arrays. For the neighborhood-scale medium arrays, considering the power-law velocity profile in the upstream free flow, a taller array gains a larger inflow rate across its windward entry and experiences younger air and greater air exchange efficiency than a lower one. If all buildings are theoretically open-based in a neighborhood-scale compact array, air becomes much younger everywhere and the air exchange efficiency doubles. In arrays of buildings with different heights, the secondary streets in front of taller buildings get younger air due to the downward flows within them. Although further investigations are still required before providing a practical framework, this paper is one of the first attempts to find ways in improving the ventilation performance in high-rise cities like Hong Kong. [Copyright &y& Elsevier]