Atmospheric pressure

19 January 2011

Dr Anil Namdeo, Senior Lecturer in Transport and Sustainability at Newcastle University, considers how air quality can be managed to improve health in an urban environment…

Over the past few decades, increased car use within urban centres has brought the problem of congestion to the forefront of the political agenda; not only because of its threat to economic growth, but also as a substantial contributor to poor air quality, noise and global warming. Since 1990, traffic has increased by one-fifth and the number of licensed vehicles has increased by 77% between 1980 and 2007, from 19 to 34 million.

It is widely acknowledged that road traffic is a major source of air pollution in the UK and in Europe. Typically, traffic produces between 50% and 80% of hydrocarbons and nitrogen oxides in large towns. In 2007, 62% of 1,3-butadiene emitted in the UK was from transport sources. Two-fifths of carbon monoxide and nitrogen oxides emissions were from transport sources, as were about one-fifth of benzene and particulate emissions. In 2007, transport represented 21% of the total greenhouse gas emission in the UK. Transport accounts for a very small proportion of sulphur dioxide and lead emissions (DfT: Transport Trends, 2009). In urban areas within the UK, the contribution of road transport to roadside pollution is such that hotspots occur. Road transport contributes far more to the public's exposure to pollutants and is responsible for up to 70% of air pollution in urban areas.

Health effects of air pollution
Nearly 3,000 anthropogenic air pollutants have been identified, of which in excess of 700 are emitted from motor vehicles. There is strong evidence that exposure to air pollution has a deleterious effect on human health. There are short-term effects on, for example, the respiratory system; and more serious impacts due to long-term exposure, including permanent reductions in lung function. Air pollution has been linked to asthma, chronic bronchitis, heart and circulatory disease, and cancer.

Carbon monoxide interferes with respiratory biochemistry and can affect the central nervous and cardiovascular systems, reducing the capacity of blood to carry oxygen and deliver it to the tissues. Nitrogen oxides and sulphur dioxide are thought to have both acute and chronic effects on respiration and lung function, particularly in people with asthma. They also contribute to the formation of ozone, which is a harmful secondary pollutant and an important greenhouse gas contributing to global warming, and to acid rain. Particulate air pollution episodes are responsible for causing premature deaths among those with pre-existing lung and heart diseases. Specific hydrocarbon components of exhaust emissions, especially polycyclic aromatic hydrocarbons bound to diesel exhaust particulates, are feared to cause cancer. Short-term exposure to benzene can cause drowsiness and dizziness. Long-term exposure can also affect bone marrow and blood production. Both benzene and 1,3-butadiene are known carcinogens.

Public concern over air quality has resulted from evidence of its links with asthma, which has increased substantially in recent decades, and its effect on children. There is evidence that the pollution from traffic exacerbates symptoms in those who are already sufferers, but little evidence that it causes asthma.

In the 1990s, there was much evidence to confirm that particulate emissions were harmful to health, and expert groups, such as the Air Quality Expert Group and the Department of Health Committee on the Medical Effects of Air Pollutants (COMEAP), all found evidence that nitrogen dioxide and particulate matter might be responsible for measurable increases in cardiovascular and respiratory diseases.

In 1998, COMEAP estimated that, on average, up to 24,000 people in the UK die prematurely every year as a result of short-term exposure to air pollution and thousands more are hospitalised. Professor Frank Kelly of the Environmental Research Group, King's College London, while giving evidence to the House of Commons Environmental Audit Committee, indicated that if new evidence was taken into account, the 1998 figure of 24,000 premature deaths per year would rise to 35,000. Research by the European Environment Agency suggests that the figure could be as high as 50,000 for the UK. Based on this evidence, in March 2010, the House of Commons Environmental Audit Committee concluded that 'poor air quality reduces the life expectancy of everyone in the UK by an average of seven to eight months and up to 50,000 people a year may die prematurely because of it'.

The government's current 2007 Air Quality Strategy estimates that particulate matter reduces life expectancy by around seven to eight months, averaged over the whole population of the UK. This is an average and for individuals who are particularly sensitive and are exposed to the poorest air quality the reduction in life expectancy could be as high as nine years. The Air Quality Strategy 2007 estimated that the health impact of man-made particulate air pollution experienced in the UK in 2005 cost between £8.5bn and £20.2bn per year. This figure is likely to be an under-estimate. The Air Quality Strategy ignores the impact on morbidity, costing only mortality. There are additional costs to the NHS from respiratory hospital admissions triggered by air pollution.

The House of Commons Environmental Audit Committee also acknowledged that, at present, the UK is failing to meet the limit values for nitrogen dioxide and particulate matter (under 10 micron in size, PM10). These exceedances occur predominantly in urban areas where the contribution to air contamination from road vehicles is high.

What can be done to reduce air pollution?
The House of Commons Environmental Audit Committee recommended that 'air quality must be a higher priority for the government. Defra must raise the profile of the issue by publicising the latest data on premature deaths more widely and making clear the benefits of improving air quality'. The committee recommended that 'local authorities are key to improving air quality' and that 'good cooperation between transport, air quality, climate change, public health and spatial planning departments, as well as with partner organisations, is essential to improving local air quality'.

Awareness needs to be raised and behaviour needs to change if air quality targets are to be met. Local air pollutants need to be controlled to reduce the risks to health, the environment and quality of life. Transport causes the most exposure to harmful air pollutants, and air quality targets will not be met without a significant shift in transport policy. Local authorities need to do more to tackle poor air quality, and they must be given information on how to develop local air quality strategies.

In order to prevent and reduce the impact of air pollution on the environment and its constituents, the UK government and devolved administrations are required under the Environment Protection Act 1995 to produce a national air quality strategy (NAQS) that contains standards, objectives and measures to improve air quality. The latest NAQS in 2007 set out objectives for key air pollutants based on the exposure assessment approach. The standards and objectives enforced in the UK are those that fall under European Union legislation. As a member of the EU, the UK is obligated to comply with its legally binding air quality limit values that must not be exceeded.

Local authorities are responsible for other functions that may affect air quality and local air quality problems are often an indirect result of measures driven by congestion, road safety or employment. Over recent years, local authorities in the UK have carried out rigorous assessments of air quality, and are delivering solutions to solve the problems of excessive levels of pollution that they have identified and declared as Air Quality Management Areas.
Exhaust emissions from vehicles are sensitive to many factors, including the ambient temperature; the engine design and size; whether or not it is operating cold or hot; the type and quantity of fuel used; the control technologies applied; the age and state of repair of the engine and exhaust system technologies; and its speed, whether it is accelerating, decelerating or idling. Driver behaviour affects emissions, with elevated levels of pollutants rising during harsh acceleration.

The stop/start, idling and slow speed characteristics of traffic, typical in urban areas, means that engines create high emissions. This is exacerbated by the large number of people who live on or in the vicinity of busy roads and drive from a cold-start into traffic jams.

Technology has an important role to play in controlling and managing traffic, thus reducing emissions and curbing the use of private vehicles. Technologies are improving air quality in the short term, reducing harmful emissions by burning fuel more efficiently. The introduction of catalytic converters has led to a significant fall in most exhaust emissions in the UK since the late 1990s. In recent years, emissions per vehicle of carbon monoxide, oxides of nitrogen, hydrocarbons and particulate matter from road transport have reduced. The largest reductions have already taken place, with substantial technical advances in engine design and after-burn treatments, such as catalysts and particle traps. More recent reductions in emissions have been achieved through the introduction of computer controlled engine management, which aims to improve efficiency and reduce fuel consumption with a consequent decrease in pollutant emissions.

Local authorities currently manage air quality using several different integrated approaches, often tailored to solve a specific environmental problem. However, a common goal to all strategies is to reduce the number of vehicles on our roads, to create a calmer and smoother movement of traffic flow, to alleviate congestion and to avoid stopping vehicles.

The solutions available to local authorities include traffic signal control and network management; public transport related infrastructure and technologies to encourage travel by public transport; demand management with park-and-ride schemes; road-user charging and speed control; and, finally, provision of public information to promote more effective use of road space in our networks, by passengers as well as freight.

Any technology that enhances modal shift could reduce vehicle emissions. Success lies not only in the coordination of the road network with and between all public transport services (bus, rail, ferry, etc.) and ensuring short walking distances at mode changes etc., but also by implementing through-ticketing processes, building design and the provision of facilities and information.

In general, curbing congestion is synonymous with reducing total pollution. So any road pricing or space rationing policy that seeks to alleviate congestion is important also for the environment.

The House of Commons Environmental Audit Committee recommended the use of low emissions zones by local authorities to improve air quality, though these schemes are costly to implement. The London low emission zone has been effective in reducing emissions of particulate matter. The Environmental Industries Commission believes that a national framework for low emission zones would help to create many new jobs in the UK's environment industry.

Park and ride schemes also have an important role to play in reducing the amount of traffic on the roads. Successful services, with high-profile buses travelling on bus-only lanes with priority at signals, have substantially reduced journey times. Nowadays, public transport and, more specifically, park and ride schemes are becoming a real and attractive alternative to the car in places, such as York, Leicester and Cambridge.

Designated bus lanes with signal priority at junctions can promote bus services. Vehicle tracking gives a wealth of information to operators to improve the reliability of services. Real-time passenger information regarding the time of arrival at bus stops makes the use of the bus more attractive.

Professors Phil Blythe and Margaret Bell CBE, of Newcastle University, have been strong proponents of the use of intelligent transport system (ITS) technologies as promising alternatives to the more traditional policy measures, such as building new roads, improving public transport infrastructure and providing acoustic screening. However, the justification for the implementation of ITS is usually to improve network safety and efficiency and to solve congestion, rather than to solve environmental and health problems, although the former often leads to the latter. Policy-makers have demonstrated the possibilities of ITS measures – such as the lowering of the speed limits or adapting traffic signals – to improve air quality and/or reduce noise levels. Vehicle control systems with intelligent speed adaptation (ISA) could, by managing speeds through satellite communication along vulnerable streets, significantly reduce air emissions. ISA has an important role to play on trunk roads and motorways to calm traffic, delay the onset of the peak and to manage capacity following incidents.

And finally, public information provision can help to cut down congestion, influence mode choice to more sustainable transport modes, and inform the public of pending air quality episodes. There are numerous technologies available to deliver information to the public to meet the needs of users. These include internet, radio, television, mobile phone, VMS, and parking information signs, to name a few.