Within the Mojave Desert Air Quality Management District (MDAQMD), sources of air pollution range from large industrial facilities and mining operations to smaller everyday sources such as gas stations, landscaping equipment, and household activities. 

Mobile sources, particularly on-road motor vehicles, remain among the largest contributors to regional air pollution.  These sources include light- and heavy-duty vehicles operating on roads and highways and, during idling, using gasoline, diesel, and other fuels.

The chart below shows emission sources of oxides of nitrogen (NOₓ), one of the primary precursors to ground-level ozone formation.  As shown, on-road vehicles account for the largest share of NOₓ emissions within the District.  Stationary sources - including industrial facilities, boilers, cement plants, power generation, and manufacturing operations - account for a smaller share of the overall emissions inventory.

While MDAQMD’s regulatory authority primarily applies to stationary sources of air pollution, mobile sources are largely regulated by the California Air Resources Board (CARB) and the U.S. Environmental Protection Agency (EPA).  Because ozone formation is heavily influenced by mobile-source emissions within and outside the District, regional coordination remains essential to improving air quality.

Although some pollutants occur naturally at low concentrations, human activity can significantly increase pollutant levels and create unhealthy air quality conditions.  Learn more about common air pollutants, their sources, and associated health effects.