Natural air pollution problems on the Earth are as old as the Earth itself. Volcanoes, fumaroles, natural fires, and desert dust have all contributed to natural air pollution. Humans first emitted air pollutants when they burned wood and cleared land (increasing windblown dust). More recently, the burning of coal; chemicals; oil, gasoline, kerosene, diesel, jet and alcohol fuels; natural gas; and waste and the release of chemicals have contributed to several major air pollution problems on a range of spatial scales. These problems include outdoor urban smog, indoor air pollution, acid deposition, Antarctic ozone depletion, global ozone reduction, and global warming.

Urban smog is characterized by the outdoor buildup of gases and particles emitted from vehicles, smokestacks, and other human sources, or formed chemically in the air from emitted precursors. Smog affects human and animal health, structures, and vegetation. Urban smog occurs over scales of tens to hundreds of kilometers.

Indoor air pollution results from the emission of pollutant gases and particles in enclosed buildings and the transport of pollutants from outdoors into buildings. Indoor air pollutants cause a variety of human health effects. Indoor air pollution occurs over scales of meters to tens of meters.

Acid deposition occurs when sulfuric acid, nitric acid, or hydrochloric acid in the air deposits to the ground as a gas or dissolved in rainwater, fogwater, or particles. Acids harm soils, lakes, forests, and structures. In high concentrations, they can harm humans. Acid deposition occurs over scales of meters to thousands of kilometers.