green areas, and between low-tech and high-tech solutions to generally, the IPCC has shown that human sources of air planning challenges. Scale has become the determining factor pollution include combustion from fossil energy production, of urban transformation: working at the neighborhood level is motorized traffic (ground, air, and maritime), household different to working at the city level. heating, industrial emissions, and emissions from agricultural areas. B- Environmental pollution and health However, the direct correlation between pollution and It is now well known that pollution, which is frequently a diseases is difficult to establish because air quality in cities byproduct of urban landscapes, is linked to climate change. is the result of a complex interaction between natural and The burning of fossil fuels, which increases CO emissions,2 human environmental conditions. For Mayer (1999), “During exacerbates both climate change and air pollution. These are transmission, air pollutants are dispersed and diluted. Some among the most important causes of global warming. The others are subjected to photochemical reactions. Ambient air COVID-19 pandemic has made it crystal clear that cities can pollution shows temporal and spatial variability.”46 However, influence human beings’ health and affect how diseases are Hoffman (2019) has more recently shown that “important health spread. Demographers and epidemiologists have highlighted effects of ambient air pollution include, but are not limited to, the health-related benefits and risk factors inherent in city life. cardiovascular and cerebrovascular disease, chronic respiratory Among the risk factors, Hoffmann (2019) discusses “sedentary disease and infections, and lung cancer, with heart disease lifestyles and exposure to air pollution, noise, heat islands and being responsible for most . . . estimated annual premature lack of green space.” She draws on scientific research that deaths.”47Young children and aging populations are particularly demonstrates the link between pollution and death rates. She suffering the negative health effects of air pollution.48 emphasizes that “among environmental risk factors, ambient air pollution is the most important cause of disease.”43 The COVID-19 pandemic has heightened policymakers’ awareness of health issues. For example, reducing the Efforts still need to be made in this area. In developing negative health impacts of urban air pollution can be countries, one relevant key concern is the global division of accomplished at different regulatory levels: international labor. Some manufacturing activities are located in countries (via the WHO), national, and local. In most cases, city-level that lack regulation or have more flexible policies when it initiatives designed to reduce air pollution—for example, comes to defining what acceptable levels of pollution are. And bicycle lanes, soft mobility programs, low emission zones, and some Western needs distort the economies of agriculture- renewable sources of energy—can also have synergistic effects based economies, because they commandeer resources such in terms of environmental change, heat stress, reduction of as land and water at the expense of the local population’s noise exposure, and potential increases in citizens’ physical needs. According to Mayer (1999), “The air pollution path of activity. Promoting the expansion of public transport options the urban atmosphere consists of emission and transmission (including by introducing new bus, streetcar, and subway of air pollutants resulting in the ambient air pollution. Each part services) and encouraging active transportation (for instance, of the path is influenced by different factors. Emissions from cycling and walking) could be the most promising strategies motor traffic are a very important source group throughout the when it comes to planning a healthy city. The ways in which world.”44 city transportation policies are defined influence quality of life in cities and affect the quality of living spaces and transport. According to Hoffmann (2019), “Traffic is the most important Moreover, city policy also deals with the quality of the air that determinant of within-city exposure contrasts, since people people breathe and of the water that they drink; populations live, work, and commute in close proximity to traffic.”45 More are now just as aware of the importance of good air and water (43) Hoffmann B. (2019). Air Pollution in Cities: Urban and Transport Planning Determinants and Health in Cities. In: Nieuwenhuijsen M., Khreis H. (eds) Integrating Human Health into Urban and Transport Planning. Springer, Cham. https://doi.org/10.1007/978-3-319-74983-9_21 (44) Mayer, H. (1999). Air pollution in cities. Atmospheric environment, 33(24-25): 4029-4037. (45) Hoffmann B. (2019). Air Pollution in Cities: Urban and Transport Planning Determinants and Health in Cities. In: Nieuwenhuijsen M., Khreis H. (eds) Integrating Human Health into Urban and Transport Planning. Springer, Cham. https://doi.org/10.1007/978-3-319-74983-9_21. (46) Mayer H. (1999). Air pollution in cities. Atmospheric environment, 33(24-25): 4029-4037. (47) Hoffmann B. (2019). Air Pollution in Cities: Urban and Transport Planning Determinants and Health in Cities.In: Nieuwenhuijsen M., Khreis H. (Eds) Integrating Human Health into Urban and Transport Planning. Springer, Cham. https://doi.org/10.1007/978-3-319-74983-9_21 (48) World Health Organization (WHO) (2018).Air pollution and child health: prescribing clean air.WHO reference number: WHO/CED/PHE/18.01. https://www.who.int/ ceh/publications/air-pollution-child-health/en/ 42 Quélin and Smadja | HEC PARIS | SMART CITIES | The sustainable program of six leading cities | 2021