A team led by Dr Jan Poloniecki at St George's Hospital Medical School in London concluded that one in 50 heart attack victims arriving at London hospitals is there as a result of poor air quality outdoors. Their research is published in the latest issue of Occupational and Environmental Medicine.
He analysed seven years of data from the late 1980s and early 1990s covering nearly 400,000 hospital admissions and levels of five key air pollutants, all produced mainly by traffic in the capital's busy roads and motorways.
The researchers were looking for a link between air quality on any one day and the number of people being rushed to hospital with heart and circulatory problems the next day. They used complex techniques of statistical analysis to probe for any connections.
They found that heart attacks, in which some of heart's muscles are killed by a lack of blood supply, rose in line with the previous day's levels of carbon monoxide, nitrogen dioxide, sulphur dioxide and particulates, microscopic sooty specks.
But these linkages between air pollution and health were found only in the colder months, from October to March, and not during the warmer April to September period. The worst pollution episodes are generally during particularly cold, still periods in winter when freezing air becomes trapped over cities and the concentration of fumes builds up over several days.
But the researchers could find no linkage between heart attacks and rising levels of low level ozone, another important pollutant known to cause discomfort to people with chest illnesses and asthma. Ozone is produced by a chain of chemical reactions which begins with traffic fumes. For high concentrations to build up there has to be little wind and long hours of strong sunshine, so ozone smogs are found only in summer.
The researchers' article says there are now ``plausible mechanisms'' by which traffic emissions might trigger blood circulation illnesses. ``Our results strengthen the case for ... a causal link with myocardial infarction [heart attacks].''
Over the past few years, a stream of big statistical studies from Europe, North America and more recently the UK have suggested a link between air pollution, deaths and hospital admissions. It seems that the elderly and those already suffering heart and lung disorders, are most at risk.
The 1990s have seen Britain and the other European Union nations implementing measures to cut pollution from new cars, lorries and buses, under EU smog- busting laws.
The most significant of these have been compulsory catalytic converters fitted to the exhaust pipes of all new cars. The annual MoT test also checks for levels of carbon monoxide in exhaust fumes. Stricter standards for new cars came into force this year, and in 2000 new vehicles will have to meet a still tougher third stage of standards.
But while these laws should bring about big improvements in air quality, and thereby save thousands of lives, there are powerful countervailing forces.
The number of cars and car usage is rising steadily, and those trends have accelerated with the strong economic recovery. For years to come, millions of older vehicles will not have catalytic converters fitted, produce copious quantities of pollutants and face no annual emissions checks. There are also worries that as cars with "cats" age, the performance of their pollution-cutting equipment falls off sharply.
The Government has forecast that air quality should now have begun improving after deteriorating through the 1980s, partly because of moves to curb traffic fumes and the drastic decline in coal burning by power stations. But it will not be possible for several years to say if things are getting better.
One reason is that a nationwide network of monitoring stations has only been in place for a few years; this makes it difficult to establish a baseline and see trends emerging. Another is that pollution levels depend on the weather and therefore fluctuate markedly from year to year, irrespective of the exact quantities being emitted.Reuse content