Urban Environmental Changes in South America: A Study on Air Pollution and Urban Heat Island over Rio de Janeiro

South American cities are great examples of late urbanization. They lack essential basic services, such as health care, mobility, water resources, and sewage supply. They are cities with different sites, historical formations, and urban spatial organization, with different environmental problems and impacts due to their millionaire populations. The Metropolitan Area of Rio de Janeiro (MARJ) is an essential example of South American metropolises. It is the second pole of demographic concentration and economic activities in Brazil, containing a large volume of activities and flows, which offers more specialized goods and services and a high urbanization rate. It is an area of intense soil occupation and many transformations throughout history and resulted in a series of modifications in the environmental system, water resources, and geomorphological, biogeographic, and atmospheric systems. In the context of the urban climate of the South American cities, this paper aims to identify the areas with the most significant potential for concentrating air pollutants and the convergence of the urban heat island in the Metropolitan Area of Rio de Janeiro (MARJ) in the current decade (2001–2020). Physical, atmospheric, and urban factors will be considered to control and define the pollution and heat in this important South American metropolis. The chapter is divided into two parts: The first one is related to air pollutants concentration in MARJ, defined from aerial basins; the second part refers to the mapping of the hot spaces (or urban heat island—UHI) in MARJ, using the land surface temperature (LST), normalized difference vegetation index (NDVI), and index‐based built‐up index (IBI). The results show that MARJ’s consolidated urban areas are the focus of air pollution and the urban heat island effect. The areas correspond to roads with a high flow of vehicles or close to air-polluting industries in lowland areas have a high potential to concentrate pollutants. Similarly, the urban areas, with high population density and built area, are the warmest and converge to the urban heat island with high LST and IBI, and low NDVI values. On the opposite, areas with a higher incidence of vegetated areas (high NDVI), with rugged landscape and without the presence of heavy industries, have a low concentration of pollutants and low LST and IBI values.