This article was updated on the 19th August 2019.
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Vehicle exhaust emissions are created when the air-fuel mixture burning inside internal combustion engines releases carbon dioxide back into the atmosphere. Diesel-powered, gasoline-powered, and hybrid vehicles all produce vehicle exhaust emissions; as the fuel used to power them contains hundreds of differently structured hydrocarbons that burn at different rates in different ways.
Vehicle exhaust emissions are also generated by the evaporation of fuel within the vehicle when the vehicle stops, and during fueling.
The composition of exhaust emissions from gasoline-powered or diesel-powered vehicles differs depending on the individual vehicle’s operating characteristics, as well as the type of fuel used. The majority of vehicle exhaust emissions are composed of carbon dioxide, nitrogen, water vapor, and oxygen in unconsumed air.
Carbon monoxide, unburned fuel, nitrogen oxides, and particulate matter such as mercury are also present in vehicle exhaust emissions in smaller quantities. A number of these substances play a significant role in vehicle-related air pollution, and carbon dioxide – a greenhouse gas – contributes to climate change.
The US Environmental Protection Agency calculates transportation as the largest source of greenhouse gas emissions in the United States, contributing to 29% of the total emissions.
Why are Vehicle Exhaust Emissions a Problem?
Vehicle exhaust emissions are a major contributor to air pollution and also cause health problems. A number of the compounds found in vehicle exhaust emissions are known to be carcinogenic in significant, long-term exposures such as those experienced by people living in large cities.
Sulfur dioxide and carbon monoxide found in vehicle exhaust emissions contribute to the creation of tropospheric or ground-level ozone. Tropospheric or ground-level ozone is developed from the interaction between two or more precursor pollutants such as nitrogen oxide and volatile organic compounds in the presence of sunlight.
This type of tropospheric ozone is believed to be responsible for poor air quality especially during the summer months and contributes to higher levels of respiratory illness as well as cancer in cities.