* Transportation: The transportation sector is the largest source of air pollution in the United States, accounting for nearly 30% of total emissions. Cars, trucks, and airplanes emit a variety of pollutants, including carbon monoxide, nitrogen oxides, and particulate matter.

* Power plants: Power plants are the second-largest source of air pollution in the United States, accounting for about 20% of total emissions. Power plants emit a variety of pollutants, including carbon dioxide, sulfur dioxide, and nitrogen oxides.

* Industrial facilities: Industrial facilities are the third-largest source of air pollution in the United States, accounting for about 15% of total emissions. Industrial facilities emit a variety of pollutants, including volatile organic compounds, hazardous air pollutants, and particulate matter.

* Residential and commercial buildings: Residential and commercial buildings are the fourth-largest source of air pollution in the United States, accounting for about 10% of total emissions. Residential and commercial buildings emit a variety of pollutants, including carbon monoxide, nitrogen oxides, and particulate matter.

* Agriculture: Agriculture is the fifth-largest source of air pollution in the United States, accounting for about 5% of total emissions. Agriculture emits a variety of pollutants, including ammonia, methane, and nitrous oxide.