even at low concentrations, airborne particles are lethal: T he great puzzle was if air pollution levels had visibly and measurably been vastly improved, how could they continue to have such detrimental effects on health? By the late 1970s, studies conducted in the us found that health damage was more strongly associated with particulate and not with sulphur dioxide.

This defied reason. Toxicologists were at a loss to explain how even small doses of particles, as shown by the results of the new studies, could have any harmful effects, let alone death. For a long time many scientists were doubtful of the result and this led to many acrimonious debates on the issue. However, eventually these new studies proved wrong everything that was earlier said or believed about there being no possible harmful health effects below a certain level of concentration.

Even more interesting is that the scientists are looking for an answer not only in the chemical properties but also in the physical property of the particles, which, simply put, means the size of a particle. Says Maynard, “This has shifted the debate in a new direction as it was suggested that very small particles might be playing the role.”

Explains Anthony Seaton of the University of Aberdeen, uk , who has researched airborne particles and their health effects, “A clue has come from the consideration of the size distribution of particles produced when fuel is burned and a realisation that the smaller they are, the greater their surface area. Therefore, their potential to carry toxic elements deep into the lung increases. The greater majority of these particles are less than 1 micron (one-fiftieth the diameter of a human hair) in diameter and most fall in the size range of 20-100 microns