Air Pollution

There are very few areas of Britain that are safe from air pollution.  Government health standards are exceeded many days throughout the year - in rural areas as well as urban.  It is estimated that air pollution causes several thousand premature deaths every year.  The health of 1 in 5 people is at risk from air pollution in the U.K.  The people who are vulnerable are young children, pregnant women, the elderly, and people suffering from heart and lung diseases. 

The impact of air pollution on health can also be assessed in monetary terms: the cost of health care, the cost of days of work lost, the economic cost of premature deaths. The National Asthma Campaign has estimated that asthma costs the UK over £1 billion per year. Environmental economists have estimated the cost of air pollution from road transport at £19.7 billion per year.

Road transport is a major source of air pollution in the UK.  In London, traffic is responsible for 99% of carbon monoxide, 76% of nitrogen oxides and 90% of hydrocarbons.  The pie chart below shows the contribution made to greenhouse gases by the transport sector was a fifth of the total amount produced in the European Union in 2001 (European Environment Agency, 2002).

When pollution levels are high, the contribution of road transport is often greater. For example, analysis by government experts shows that when particulate levels exceed health standards, then road traffic's contribution is in the range of 75-85% (more details about carbon monoxide, nitrogen oxide, hydrocarbons and particulates are provided below).  Summertime smog, or ozone, is also caused by traffic.  It does not come directly from vehicles or factories but is created by chemical reactions between other nitrogen oxides and hydrocarbons. How traffic produces air pollution and steps we can take to reduce it are outlined next.  

Pollutants and How They are Caused

The internal combustion engine has been developed into a powerful, reliable and compact power unit.  These engines work by burning fuel in cylinders and expansion of this burning fuel pushes a piston down.  The piston in turn pushes a crankshaft around; much like a person's legs pushes the pedals around the crank on a pushbike.  The rotary motion of the crankshaft is then used to power the transmission that allows the vehicle to be driven at different speeds.  The big disadvantage of these engines is the combination of impurities in the fuel and the process of burning it produces pollutants.

The Four Stroke Internal Combustion Engine

The pollutants that are produced by internal combustion engines are: nitrogen dioxide, carbon monoxide, benzene, particulates and hydrocarbons.  The problems associated with these different pollutants are given below:

Nitrogen dioxide: May aggravate asthma symptoms. Can cause a tightening of the chest and reduced lung function. Can make airways more sensitive to allergens such as house dust mite. By disrupting the body's natural cleansing mechanisms nitrogen dioxide may increase the body's susceptibility to viral infections.

Carbon monoxide: Slows reflexes, impairs thinking and causes drowsiness by reducing the oxygen-carrying capacity of the blood. Can increase the likelihood of exercise- related pain in people with coronary heart disease.

Benzene: A known carcinogen (something that causes cancer) that can cause leukaemia.

Particulates: Consistent correlation between particle levels and death rates. High levels of particles have also been linked with increased hospital admissions and asthma attacks. Smaller particles can carry carcinogenic particles into the lungs.

Hydrocarbons (Ozone): Irritates the mucous membrane of the respiratory system, causing coughing, choking and impaired lung function, particularly in people who exercise. Other symptoms include headaches, eye nose / throat irritation and chest pain on deep breathing. Can make airways more sensitive to allergens such as pollen. Can also impair defences against bacteria and viruses.  

Reducing Pollution

A new car meeting the latest toxic emissions standards is around 30 times cleaner than a new car in the early 1980’s. There are three main reasons for this: improvements in fuel, cars being more fuel-efficient and the use of catalytic converters.

Petrol used to have lead added to it get a higher octane number and therefore more power. Lead emissions have decreased by about 91.5% since the late 1980s. This is because the amount of lead allowed in petrol was reduced in 1985 and was banned in 2000.  In more recent times, petrol companies have been decreasing the amount of sulphur added to petrol.

Cars are using less fuel than they used to.  It is now common to have 5 speed gearboxes (and some now have 6) whereas the norm used to be 4.  Engines are more efficient and cars are more aerodynamic.  The rise in the use of diesel cars has helped although these produce more particle emissions.   Fuel consumption per passenger kilometre fell by about 10 per cent during the 1980s, as distance travelled by passengers increased by more than fuel used by passenger vehicles. Following increases in the early 1990s, there have been further reductions, and by 2002 fuel consumed per passenger kilometre was 13% per cent lower than it had been in 1980.

Although road transport users remain the main producers of carbon monoxide, there has been a substantial reduction in emissions since 1990. Levels have fallen sharply since 1990, from 5.5 to 2.3 million tonnes, despite increased traffic. This is primarily due to the introduction of catalytic converters on petrol cars that help reduce toxic emissions (see diagram below).

Catalytic Converter

Even though average carbon dioxide emissions from new cars have reduced over recent years, increases in car ownership and mileage mean that total carbon emissions from road transport haven't decreased for the last decade.  The government has set some targets for carbon emissions and at the moment progress has not been swift enough to meet the targets.  For example, the target for a 25% reduction in carbon dioxide emissions for 2008 set in 1998 is behind schedule (a reduction of 9% had been achieved by 2003).  One promising way of reducing emissions is to change the way we power our cars.  Hybrid and hydrogen powered cars have a great deal of promise - for more info click here.

There are several other measures that can be used to help reduce the amount of road traffic pollution.  These include urban traffic management, junction control, parking restrictions or traffic calming.  The table below (TRL, Report 174) outlines some possible advantages and disadvantages of these measures.  On faster roads, such as busy motorways, reducing the speed limit during heavy traffic can help keep the traffic moving and therefore reduce pollution.  For more about controlled motorways read about the M25's variable speed limits.

Traffic Management Schemes