How does urban sprawl contribute to air pollution?

Construction equipment emits fumes. There's more cars on the road, more industries. Basically, lots more fumes.

Urban sprawl refers to the expansion of poorly planned, low-density, auto-dependent development, which spreads out over large amounts of land, putting long distances between homes, stores, and work and creating a high segregation between residential and commercial uses with harmful impacts on the people living in these areas and the ecosystems and wildlife that have been displaced. Although some would argue that urban sprawl has its benefits, such as creating local economic growth, urban sprawl has many negative consequences for residents and the environment, such as higher water and air pollution, increased traffic fatalities and jams, loss of agricultural capacity, increased car dependency, higher taxes, increased runoff into rivers and lakes, harmful effects on human health, including higher rates of obesity, high blood pressure, hypertension and chronic diseases, increased flooding, decrease in social capital and loss of natural habitats, wildlife and open space. In its path, urban sprawl consumes immeasurable acres of forests, farmland, woodlands and wetlands and in its wake, leaves vacant storefronts, boarded up houses, closed businesses, abandoned and usually contaminated industrial sites, and traffic congestion, which can stretch miles from urban centers and is creating a hidden debt of unfunded infrastructure and services, urban decay, social dysfunction, and environmental degradation.