Motor vehicle emissions are composed of the by-products that comes out of the exhaust systems or other emissions such as gasoline evaporation. These emissions contribute to air pollution and are a major ingredient in the creation of smog in some large cities.[2][3][4][5]
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Mono-nitrogen oxides NO and NO2 react with ammonia, moisture, and other compounds to form nitric acid vapor and related particles. Small particles can penetrate deeply into sensitive lung tissue and damage it, causing premature death in extreme cases. Inhalation of such particles may cause or worsen respiratory diseases such as emphysema, bronchitis it may also aggravate existing heart disease.[7][8][9] In a 2005 U.S. EPA study the largest emissions of NOx came from on road motor vehicles, with the second largest contributor being non road equipment which is mostly gasoline and diesel stations.[9]
When oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight, ground level ozone is formed, a primary ingredient in smog. A 2005 U.S. EPA report gives road vehicles as the second largest source of VOCs in the U.S. at 26% and 19% are from non road equipment which is mostly gasoline and diesel stations.[10] 27% of VOC emissions are from solvents which are used in the manufacturer of paints and paint thinners and other uses.[11]
Ozone is beneficial in the upper atmosphere, but at ground level ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity.[12] In the United States, ozone is responsible for an estimated $500 million in reduced crop production each year.[13]
Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries.[14] Carbon monoxide is colorless, odorless and tasteless, but highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily tissues. In the U.S. 60% of carbon monoxide is caused by on road vehicles.[15]
Chronic (long-term) exposure to benzene (C6H6) damages bone marrow. It can also cause excessive bleeding and depress the immune system, increasing the chance of infection. Benzene causes leukemia and is associated with other blood cancers and pre-cancers of the blood.[16][17]
The health effects of inhaling particulate matter have been widely studied in humans and animals and include asthma, lung cancer, cardiovascular issues, and premature death. Because of the size of the particles, they can penetrate the deepest part of the lungs.[18] A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM.[19] In a 2006 publication, the U.S. Federal Highway Administration (FHWA) state that in 2002 about 1 per-cent of all PM10 and 2 per-cent of all PM2.5 emissions came from the exhaust of on-road motor vehicles (mostly from diesel engines).[20]
Carbon dioxide is a greenhouse gas. Motor vehicle CO2 emissions are part of the anthropogenic contribution to the growth of CO2 concentrations in the atmosphere which is believed by a majority of scientists to play a significant part in climate change. Motor vehicles are calculated to generate about 20 per-cent of the European Union's man-made CO2 emissions, with passenger cars contributing about 12 per-cent.[21] The European Union average new car CO2 emissions figure dropped by 5.4 per-cent in the year to the first quarter of 2010, down to 145.6 g/km.[22]
| Component | Emission Rate | Annual pollution emitted |
|---|---|---|
| Hydrocarbons | 2.80 grams/mile | 77.1 pounds (35.0 kg) |
| Carbon Monoxide | 20.9 grams/mile | 575 pounds (261 kg) |
| NOx | 1.39 grams/mile | 38.2 pounds (17.3 kg) |
| Carbon Dioxide - Green house gas | 0.916 pounds per mile (258 g/km) | 11,450 pounds (5,190 kg) |
The California Air Resources Board (C.A.R.B.) found in studies that 50% or more of the air pollution (smog) in Southern California is due to car emissions.[24]