Understanding Emissions from Motor Vehicles
When fuel is burnt inside the combustion chamber of an engine chemical energy in the fuel is converted into heat and kinetic energy. The heat is lost to the atmosphere and the kinetic energy propels the car. The fuel itself is converted into low energy waste products which eventually come out of the exhaust pipe. Some of these can be harmful to human health and the environment, especially if released in large quantities.
There are two major concerns associated with car exhaust emissions:
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Air pollutants such as carbon monoxide, nitrogen oxides, particulate matter, volatile organic compounds, benzene and many others are emitted into the environment by motor vehicles. Air pollutants can contribute to urban air quality problems, for example photochemical smog, as well as adversely affect human health and the health of other living things. More information on the impacts and sources of air pollutants is available from the Department of Sustainability, Environment, Water, Population and Communities.
Data from the National Pollutant Inventory indicates that in Australia motor vehicles remain a major source of air pollutants in urban areas.
However, not all vehicles contribute the same amount of air pollution to the atmosphere. When you use the Green Vehicle Guide, look for vehicles which have a higher Air Pollution Rating.
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Motor vehicles emit greenhouse gases. In vehicles, the principal greenhouse gas is carbon dioxide but vehicles also produce nitrous oxide and methane, which contribute to climate change.
The road transport sector depends on petroleum based fuels. Growth in the Australian road transport task has led to a corresponding increase in fuel consumption, which in turn, has led to an increase in greenhouse gas emissions from the sector. In 2009, road transport accounted for 13.2% of Australia's total greenhouse gas emissions. Specifically passenger cars accounted for 7.5% and trucks/buses 5.5% of Australia's total greenhouse gas emissions. Greenhouse emissions from road transport have been increasing at an average rate of 1.4% per annum since 1990 .
The Australian Greenhouse Office maintains the National Greenhouse Gas Inventory which has more information on the emissions of greenhouse gases in Australia.
Again, not all vehicles will have the same impact on climate change. When you use the Green Vehicle Guide, a higher score on Greenhouse Rating means the car produces lower levels of carbon dioxide.
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 See 'National Inventory Report 2009 - Volume 1', at: http://www.climatechange.gov.au/~/media/publications/greenhouse-acctg/national-inventory-report-2009-vol1.pdf.