An aerosol is a suspension of liquid or solid particles in a gas. Examples are smoke, clouds, and dust.
Ambient aerosols are a complicated mixture of particles emitted from various sources after atmospheric reactions. The aerosol makeup is dynamic, diverse, and largely depends on local emission profiles and meteorological conditions. To date, researchers in the field are still trying to obtain more information on the aerosol chemical and physical characteristics so that they can eventually appropriately identify the sources and effectively control air pollution problems.
Aerosols are regulated by the EPA by particulate matter (PM) standards PM10 and PM2.5 based on their aerodynamic size. The hightest concetrations of aerosols are found in urban areas due to fossil fuel combustion due to transportation and industrial sources.