Any visible or invisible particle or gas found in the air that is not part of the original, normal composition. Natural: forest fires, pollen, dust storm
Unnatural: man-made; coal, wood and other fuels used in cars, homes, and factories for energy
Any visible or invisible particle or gas found in the air that is not part of the original, normal composition.Natural: forest fires, pollen, dust stormUnnatural: man-made; coal, wood and other fuels used in cars, homes, and factories for energy