Concern over particles

That airborne particles kill has been known for a while. But the threat is rising with every scientific discovery

There is nothing new about particulate pollution. Yet, scientists are talking about airborne particles today like never before. As science on air pollution developed in response to environmental and public health crises in the West, these tiny killers came under intense scrutiny. Today, scientists are perplexed by the discovery that even at very low concentrations these particles kill. They have now shifted their focus to the tiniest and the most lethal of them all and their potential to claim lives. This has dramatically altered the approach to its risk management worldwide.

Scientists had known all along that particles are harmful but scientific evidence on the enormity of their health effects is yet to be understood completely. The history of particles goes back many hundred years. Records tell us that during the rule of Edward I (1272-1307 ad) burning of coal was banned in London to control air pollution. His successor Edward II actually ordered persons guilty on this count to be tortured. As the West industrialised and motorised fast, it went through a series of severe air pollution episodes in the early 20th century. Smoke particles and sulphur dioxide were the most talked about pollutants in those days. The first recorded episode was in Meuse valley of Belgium where air pollutants got trapped at ground level for a week in December 1930 killing 60 people. Across the Atlantic, in October 1948, half the population of 14,000 in Donora, Pennsylvania, fell sick, 10 per cent fell severely ill and 20 died due to severe air pollution. But it took the notorious London Smog of 1952 which killed 4,000 people to trigger extensive research on air pollution and its effects on health which ultimately revealed deadly facts about smoke particles.

When the uk government, alarmed by the death count of the 1952 smog episode in London, enforced more stringent air pollution control methods, they actually succeeded in bringing the level of pollution down. Paradoxically, this success in lowering pollution only proved that the objective of reducing risk from the killer particles was still very distant.

Immediately after air pollution levels fell in London following strict enforcement of air pollution measures, it first became more and more difficult to detect the effects on health of day-to-day variation in concentration of smoke. Robert L Maynard of the department of health, uk, who has recently edited a study entitled Particulate Matter: properties and effects upon health , says that this led scientists to believe that it is possible to set a threshold limit for pollutants below which health effects are unlikely to occur. Therefore, setting safe limits for air pollutants was the most obvious thing to do. This led to establishment of guidelines for air pollutants including particulates in uk and these later provided the basis for the World Health Organisation's Air Quality Guidelines for Europe in 1987 and air quality regulations worldwide.

But things changed dramatically when scientists began to observe incomprehensible but serious health effects even at extremely low concentrations of particles. Says Maynard, "A trickle of epidemiological studies that began in the late 1980s and turned into a flood gate in the 1990s provided evidence that day to day variations in the already low concentrations of particles and other pollutants were still associated with effects on health.'

As science on particles developed, scientists were faced with more questions than they had solutions for. It was clear to them that they needed to understand much more about the