The 1st Edge Debate: 18th June 1996

Death to Breath It? Air Quality and Health

Dr Malcolm Green

President, The British Lung Foundation

The haze of photochemical smog that collects over our cities has been seen by most people during hot summer spells. Whilst this can make for multi-coloured sunsets, we can be less sanguine about the health effects of this summer pollution.

Air pollution was recognised in Rome, and by mediaeval times small scale industries and domestic heating were creating problems with pollutants in Britain. Thus, by 1307, Edward I issued proclamations forbiding the burning of sea-coal in furnaces and lime kilns. However his measures were not effective and the burning of coal continued so that by 1600 London's air was intolerably pulluted. The diarist John Evelyn, living in the 17th century Age of Enlightenment, concluded that London's pollution was man-made, due to lack of urban planning and controls and mainly due to the burning of coal. His influential work ‘the inconvenience of the aer and the smoak of London dissipated' was published in 1661 and had a major impact on the thinking of the day, but little effect on the sources of pollution.

The Industrial Revolution of the 18th and 19th centuries brought massive expansion in the burning of fossil fuels, with a corresponding dramatic decrease in the quality of air across the country and particularly in cities. The fogs of London started to become infamous, and caused increasing anxiety. Finally in December 1952 there occurred a smog in London of such severity that national action was imperative. During this episode in one week there were 4,000 excess deaths and the careful epidemiological research which documented this led to public outcry. The Clean Air Acts were passed in 1956 and 1968 and the Clean Air Councils set up. These measures had the benefit of public understanding and support, enabling effective measures for smoke abatement from domestic and industrial sources.The combination of public pressure, Government commitment and appropriate regulations was successful and resulted in a dramatic improvement in air quality.

Unfortunately over the last 15 years a new form of air pollution has increasingly afflicted the UK, and particularly its large cities. This is due to the ever increasing number of vehicles on the roads, and miles travelled by them. Classic industrial air pollution was made up largely of smoke and sulphur dioxide, derived mainly from the burning of coal. Vehicle exhausts, on the other hand, emit a cocktail of pollutants which include the oxides of nitrogen (particularly nitrogen dioxide), carbon monoxide, hydrocarbons, particulates and lead. On hot still days these accumulate over cities and the countryside, together with low concentrations of industrial pollutants, and undergo further reactions catalysed by sunlight to form ozone and acidic aerosols.

The health effects of air pollution have been the subject of considerable research over the past decade, particularly in Europe and the United States. Only in the last few years has scientific research in the UK started to focus on these new forms of pollution.

The most widely publicised pollutant is lead, which is known to impair the neuropsychological development of children. Effective Government action has led to the reduction of lead levels in petrol, and fiscal measures have encouraged the use of unleaded petrol. This has resulted in a substantial fall in the concentrations of lead in the environment, and an improvement in the blood levels of children.

The health effects of the individual parts of the pollution cocktail are complex, and can be difficult to disentangle. However nitrogen dioxide can be a respiratory irritant and an episode of severe nitrogen dioxide pollution in London in December 1991 was associated with an excess mortality calculated as 120 deaths. Ozone, a secondary pollutant, is a highly reactive substance which can increase bronchial responsiveness and impair lung function in a proportion of normal subjects as well as in people with asthma and irritable airways.

Carbon monoxide is rapidly absorbed through the lungs into the bloodstream where it combines with the red blood cells and impairs the transport of oxygen to the tissues. Exposure to concentrations sometimes encountered in heavy traffic can impair heart function, and exacerbate angina and coronary artery disease.

A number of epidemiological studies have now shown that particulates, the tiny particles of hydrocarbons which are particularly emitted by diesel vehicles, to be unexpectedly toxic. These particulates can be inhaled deep into the lungs and are consistently associated with increase in infections in the elderly, respiratory admissions to hospital, and increase in death rate. This leads to the conclusion that diesel engines are no more environmentally friendly than petrol engines.

The prevalence of asthma is increasing in Western society. The cause of this remains uncertain. There is little hard evidence to blame air pollution although it is certainly known that air pollutants, and particularly ozone, can exacerbate asthma. Most patients with respiratory diseases find that atmospheric pollution, whether from cigarette smoke or vehicle exhausts, exacerbates their symptoms. If pollution can exacerbate asthma it is plausible that it plays a part in tipping at least some susceptible people over into having clinical manifestations and frank asthma.

There has been a plethora of reviews by expert groups in the UK over the last five years including the Royal Commission on Environmental Pollution. The general concensus of these groups and their reports is that, while Britain does not have a crisis of the proportions to that in 1952, air pollution is an important health issue. Even at the concentrations in our cities today air pollution has a detrimental effect on health. We have not reached the levels of persistent pollution seen in Mexico City or Athens, but there is no room for complacency.

Improving the quality of air is not easy, and requires a commitment by individuals as well as local and national regulations. In the first instance we must ensure that vehicles pollute as little as possible. From 1993 catalytic converters have been mandatory on new small cars, so this technology will gradually work through the vehicle fleet over the next decade or two. These do reduce exhaust emissions or carbon monoxide, nitrogen oxides and hydrocarbons, but their effects should not be over-estimated. Catalytic converters need maintenance, work less efficiently at low speeds, and have not been developed for diesel powered vehicles. We must ensure that all vehicles are regularly tested for emissions, and that strict controls are enforced, if necessary taking vehicles off the roads if they are polluting intolerably. Whilst catalytic traps have been recently developed for diesels, it is difficult to fit these retro-actively, they are relatively expensive, and have not yet been widely introduced.

In the longer term the most effective way of ensuring cleaner air for our lungs is to lower our dependence on the internal combustion engine. We must develop a rational, national transport policy. This should include improved safe and cheap public transport. Measures should be taken to encourage safe walking and cycling, particularly as most journeys are less than three miles. Unrestricted expansion in our use of private cars is not environmentally sustainable, particularly on our small island. We must therefore think about designing our society in such a way that we do not ever increasingly require our citizens to use private transport for work, shopping, leisure and other activities.

This may mean re-analysing our urban design, re-vitalising inner cities, discouraging the spread of out-of-town shopping malls and returning to a smaller scale of relatively self-sufficient local communities.

These measures will require a shift in attitude by the public, planners and Government alike. However a compromise will have to be reached with the internal combustion engine. As a society we have now started to come to terms with its adverse effects, and this process is likely to gather momentum over the forthcoming years. We need to ensure that the internal combustion engine becomes our servant, rather than our master. Let us start this process now, with rational debate and a proactive approach to our environment, and the health of our lungs.

Dr Malcolm Green is President of the British Lung Foundation, Director of the British Postgraduate Medical Federation, Honorary Senior Lecturer at the National Heart and Lung Institute and Consultant Physician to the Royal Brompton Hospital, where he runs a clinical practice in respiratory medicine.