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What Causes Air Pollution?

Air Quality Toolkit for Local Governments

The Sources of Air Pollution
A number of sources – activities that cause pollution to be emitted into the air – contribute to poor air quality and ground-level ozone formation. Human-generated sources are categorized as follows:


Are classified as on-road and non-road vehicle sources. On-road sources include vehicles traveling on roads to transport passengers or freight. Non-road sources include gas and diesel powered vehicles, engines and other equipment used for aircraft, construction, agriculture, recreation, and more.


Nearly two-thirds of ozone-causing emissions come from the direct actions of people who live and work in the region and the services they require.


Are smaller emissions sources that collectively account for a significant portion of air pollution. These include producers such as lawn mowers, certain types of trees, home and personal care products, after-market auto care products, paints and solvents, residential and commercial heating, and breweries and other small production businesses, among others.


Are fixed-site producers of pollution such as power plants, chemical plants, oil refineries, manufacturing facilities, small industrial processes, and other industrial operations. Large sources that have specific locations and release pollutants in quantities above a certain threshold are known as point sources. The State of Colorado requires that the producers of these sources file an Air Pollution Emission Notice (APEN) with the Colorado Department of Public Health and Environment, which maintains a Stationary Source Emissions Inventory.