undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities

rain containing acids that form in the atmosphere when industrial gas emissions (especially sulfur dioxide and nitrogen oxides) combine with water

pollution resulting from an industrial plant discharging pollutants into the atmosphere

unhealthy vapors rising from the ground or other sources

air pollution caused by fine particles of soot (as from power plants or diesel engines)

air pollution by a mixture of smoke and fog