Which areas in the United States are most seriously affected by air pollution?

The most seriously affected areas by air pollution in the United States are urban downtowns. These regions typically experience higher levels of air pollution due to the concentration of vehicles, industrial facilities, and population density. Urban areas often have significant emissions from transportation and energy production, which lead to increased levels of pollutants such as nitrogen oxides, particulate matter, and volatile organic compounds.

High-elevation slopes facing moving air masses are generally less populated and may also benefit from the dispersion of pollutants due to wind patterns. Coastal areas, while they can have localized pollution issues, often have more natural dispersion mechanisms due to ocean breezes. Rural farmlands may experience some air pollution, particularly from agricultural practices, but they do not have the same level of persistent, concentrated pollution sources found in urban downtowns. Therefore, urban downtowns stand out as the areas most seriously affected by air pollution in the United States.