The emissions from petrol and diesel combustion engines include carbon dioxide (CO2) and carbon monoxide (CO). Partially burnt fuel is present in the exhaust gases forming a complex cocktail of hydrocarbons (HCs) such as methane (CH4). Particulate matter (PM) and nitrogen oxides (NOx) is also produced and is especially prevalent in diesel exhaust.
Road transport emissionsReturn to top
Vehicle emissions contribute to the increasing concentration of gases that are leading to climate change. In order of significance, the principal greenhouse gases associated with road transport are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Road transport is the third largest source of UK greenhouse gases and accounts for over 20% of total emissions. Of the total greenhouse gas emissions from transport, over 85% are due to CO2 emissions from road vehicles. The transport sector is the fastest growing source of greenhouse gases.
Road transport also remains the main source of many local emissions including benzene, 1,3-butadiene, carbon monoxide (CO), nitrogen oxides (NOx) and particulates (PMs). Within urban areas, the percentage of contributions due to road transport is particularly high - in London road transport contributes almost 80% of particulate emissions. There is a growing body of evidence to link vehicle pollutants to human ill health including the incidence of respiratory and cardio-pulmonary disease and lung cancer.
In 1998 the Committee on the Medical Effects of Air Pollutants estimated that up to 24,000 people die prematurely each year in the UK as a direct result of air pollution. Similar findings are emerging from international research. According the World Health Organisations estimates air pollution was responsilbe for the death on 3.7 million people under the age of 60 in 2012.
References: Holgate, S. Quantification of the Effects of Air Pollution on Health in the United Kingdom. The Stationery Office, London, 1998
EU vehicle emissions standards Return to top
European directives have been instrumental in reducing what are known as the regulated emissions. These include carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HCs) and particulate matter less than 10 microns in size (PM10). First introduced in 1992, these form a set of rolling regulations designed to become more stringent year on year. Currently limits for new cars and light-duty vans must conform to 'Euro IV' standards.
The effect of tighter Euro standards on vehicle emissions has been to accelerate the introduction of greener vehicle technologies. For petrol cars, this has been achieved in part through the use of the three-way catalytic converter and the move to fuel injection systems. For diesels, NOx and particulate emissions have been reduced through the development of direct injection engines and diesel particulate filters (DPFs).
These technological advances, together with the cleaner fuels that made these developments possible, have led to a dramatic reduction in regulated pollutants; so much so, that a car manufactured today produces twenty times fewer emissions than a car made in 1970. Car manufacturers are well aware that future cars will have to conform to yet tighter regulations – indeed, while Euro V came into force in 2010, tighter standards will come into force in 2015 (Euro VI).
In contrast to the legislation for regulated pollutants, there was until recently no current EU law which limits the amount of carbon dioxide produced by cars. However, in 2009, the European Parliament passed new car CO2 legislation that sets an emissions cap of 130 g/km averaged over all new vehicles produced by each manufacturer by 2015. The 130 g/km average will be the equivalent of 58 mpg for diesel engines and 52 mpg for petrol engines.
An extended target is set to be an average of 95 g/km by 2021. Manufacturers exceeding targets from 2012 have to pay a penalty for each car registered, which amounts to €5 for the first g/km of over the limit, €15 for the second g/km, €25 for the third, and €95 for each subsequent gram. From 2019, stricter penalties will be introduced with every exceeding gram costing the manufacturer €95.
EU emissions standards for passenger cars (in g/km)
|Euro Standard||Implementation date*||CO
|Euro I||July 1993||2.72||-||-||-||0.97||0.14|
|Euro II||January 1997||1.00||-||-||-||0.70||0.08|
|Euro III||January 2001||0.64||-||-||0.50||0.56||0.05|
|Euro IV||January 2006||0.50||-||-||0.25||0.30||0.025|
|Euro V||September 2010||0.500||-||-||0.180||0.230||0.005|
|Euro VI||September 2015||0.500||-||-||0.080||0.170||0.005|
|Euro I||July 1993||2.72||-||-||-||0.97||-|
|Euro II||January 1997||2.20||-||-||-||0.50||-|
|Euro III||January 2001||2.30||0.20||-||0.15||-||-|
|Euro IV||January 2006||1.00||0.10||-||0.08||-||-|
|Euro V||September 2010||1.000||0.100||0.068||0.060||-||0.005**|
|Euro VI||September 2015||0.100||0.100||0.068||0.060||-||0.005**|
|* Market placement (or first registration) dates, after which all new engines placed on the market must meet the standard. EU emission standards also specify Type Approval dates (usually one year before the respective market placement dates) after which all newly type approved models must meet the standard.
** Applies only to vehicles with direct injection engines.
Effects of vehicle emissionsReturn to top
Carbon Dioxide (CO2)
While carbon dioxide is non-toxic, its main environmental effect is as a greenhouse gas. Each year an estimated 30 billion tonnes of carbon dioxide are emitted due to human activity, 2% of which originates from the United Kingdom.
To illustrate the scale of the impact of these emissions as a result of human activities, the atmospheric concentration of carbon dioxide (from all sources) has increased by 31% since 1750. The present concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years. Over the last two decades, about three-quarters of the anthropogenic emissions of carbon dioxide have been a result of burning of fossil fuels, the rest being predominantly due to land-use change (eg deforestation).
By enhancing the greenhouse effect, greenhouse gas emissions are leading to increases of the Earth's atmospheric, land and sea temperatures. During the 20th century the global average surface temperature (the average of near surface air temperature over land and sea surface temperature) increased by 0.6 (+/-0.2)degC. This temperature is predicted to increase by 1.4-5.8degC by 2100 (1990 baseline). Based on palaeo-climate data, the projected rate of warming is very likely to be without precedent during at least the last 10,000 years. The concomitant rises in sea levels and resulting climatic change will be of great (and as yet unknown) significance to all patterns of life on Earth.
Carbon Monoxide (CO)
Produced during the incomplete combustion of carbon compounds such as fossil fuels, this gas is known to be deleterious to human health. During respiration it readily combines with haemoglobin in the blood thus hindering the body's ability to take up oxygen. It is thought therefore to aggravate respiratory and heart disease.
Carbon monoxide also contributes to global warming to a small degree. This it does indirectly after first taking part in chemical reactions within the atmosphere. One such reaction would be with oxygen, forming carbon dioxide and thus contributing to the enhanced greenhouse effect.
Nitrogen Oxides (NOx)
As a result of the high temperatures occurring during combustion, nitrogen combines with oxygen from the air forming oxides of nitrogen (NO, NO2, N2O etc.). These gases are known to be responsible for acid deposition via the formation of nitric acid. Nitrogen dioxide (NO2) is toxic even in small concentrations and is known to cause and aggravate human respiratory diseases. Nitrous oxide (N2O) also contributes directly to global warming and is responsible for around 7% of the enhanced greenhouse effect.
Particulates, commonly known as 'black smoke', are fine particles produced by incomplete combustion, the burning of lubrication oil and by the presence of impurities within the fuel. Typically with a dimension of the order of 10 microns or less (known as 'PM10'), they are known to cause and aggravate human respiratory diseases and are thought to be carcinogenic. The World Health Organisation has issued a report stating that there are no concentrations of airborne micro-sized particulate matter that are not hazardous to human health.
Volatile Organic Compounds (VOCs)
Volatile organic compounds consist of a number of different chemicals including hydrocarbons (eg methane), which are released during the production, refining, storage and combustion of fossil fuels. The largest environmental risks of VOCs are due to the presence of benzene and 1,3-butadiene, which are both carcinogens and are easily inhaled due to their volatile nature. Other chemicals in this category are responsible for the production of tropospheric ozone, which is toxic even in low concentrations.
Methane is a significant greenhouse gas and is released during the drilling for oil and gas and during the combustion of petroleum products. Around 5% of methane emissions are due to the production and use of fuels used for road transport.
Tropospheric Ozone (O3)
In the stratosphere, ozone absorbs ultraviolet light, therefore reducing the number of harmful rays reaching living organisms at the Earth's surface. However, at ground level (the troposphere), ozone is toxic to animals and plants. Ozone is thought to be responsible for aggravating human respiratory disease and is known to reduce crop yields.
While the concentration of stratospheric ozone is being depleted by the action of chlorofluorocarbons and other chemicals, exhaust emissions from road vehicles are increasing the concentration of ozone at ground level. Although there are a number of sources of man-made tropospheric ozone, transport is known to be a major contributor of emissions through the action of sunlight on emitted VOCs.
Lead is known to affect the mental development of young children and is known to be toxic. It was originally introduced into petroleum products as an 'anti-knock' additive to improve combustion in a spark-ignition (petrol) engine. At its peak, road transport was responsible for three quarters of airborne lead in the UK. However, due to the introduction of unleaded petrol and the elimination of leaded fuels in Europe in 2000, the amount of lead emitted has fallen by over 80%.
References: Motor Vehicle Pollution, Reduction Strategies Beyond 2010. Organisation for Economic Co-operation and Development, Paris; Holgate, S. Quantification of the Effects of Air Pollution on Health in the United Kingdom. The Stationery Office, London, 1998; One in three child deaths in Europe due to environment. World Health Organisation, June 2004. Available online: http://www.euro.who.int/mediacentre/PR/2004/20040617_1; Environmental Impacts of Road Vehicles in Use. Cleaner Vehicles Task Force, Department of the Environment, Transport and the Regions, 1999, The Stationery Office, London; Climate Change UK Draft Programme, 2000. Department of the Environment, Transport and the Regions. The Stationery Office, London.
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