Air pollutionUnited States

Air pollution is contamination of the air by gases, particles or other substances that can adversely affect human health, the environment or ecosystems.

Vehicles produce pollutants through fuel combustion, exhaust systems, brake wear, tyre wear and road-surface interaction. Moving traffic can also resuspend dust already present on the road.

Important traffic-related pollutants include nitrogen oxides, particulate matter, carbon monoxide and volatile organic compounds. Their relative importance depends on the vehicle, fuel and driving conditions.

Nitrogen dioxide (NO2) is an air pollutant associated particularly with combustion processes and road traffic. High concentrations are commonly found near busy roads and densely trafficked urban areas.

Particulate matter consists of tiny solid particles or liquid droplets suspended in the air. Road traffic can produce particles from exhaust, brakes, tyres and road surfaces.

No. Carbon dioxide is primarily regulated as a greenhouse gas because of its contribution to climate change. Local air-quality pollution generally focuses on substances such as nitrogen dioxide, particulate matter, ozone and other pollutants that directly affect air quality and health.

Fully electric vehicles produce no combustion-engine exhaust emissions while driving, but they can still contribute to non-exhaust particulate emissions through tyres, brakes and road wear.

Yes. Concentrations of traffic-related pollutants can be higher close to heavily trafficked roads because many emissions occur close to ground level and near where people live and travel.

A low-emission zone is an area where access by more polluting vehicles is restricted in order to reduce traffic-related air pollution. Access criteria may depend on factors such as fuel type, vehicle category and emission standard.

Measures include cleaner vehicles, stricter emission standards, effective emission-control equipment, low-emission zones, public transport, cycling and walking, as well as traffic-management measures that reduce unnecessary congestion and emissions.