SPECIAL ISSUE ON PARTICULATE AIR-POLLUTION - HEALTH-EFFECTS OF PARTICULATE POLLUTION - REAPPRAISING THE EVIDENCE

Governments, in setting standards, must try to avoid harm, and a balance has to be reached between the costs of implementation of standards of emission and the possible harm or possible benefit to human groups caused or avoided. The evidence that we have reviewed in this report does not substantiate any level of air pollution below 250 μg/m3, smoke (BS) as a 24-hour average, as having a harmful effect on health. Furthermore, the studies undertaken so far are not capable of distinguishing the harmful effects of the various pollutants in the atmosphere. Most of those that have shown a harmful effect above levels of 250 μg/m3, smoke (BS) as a 24-hour average, have been in areas where levels of other pollutants are high, in particular the sulfur oxides. The attempt to differentiate between the different pollutants to form a reliable foundation for setting air quality standards for individual air pollutants is an extremely complex procedure. Unfortunately, governments, industry and scientific groups have not yet combined to determine how best to approach this problem, which is of profound significance. The authors conclude, therefore, on the basis of current knowledge, that the quantitative concentrations of suspended particulate matter at which health effects may appear are those summarized in table 1. The lowest annual average levels at which transient health effects are discernible in sensitive groups, including children, are at levels in excess of about 140 μg/m3 smoke (BS) annual mean (total suspended particulate (HV) equivalent above about 240 μg/m3) in the presence of sulfur dioxide 180 μg/m3 annual mean. The lowest 24-hour average levels at which increased incidence of illness in bronchitic patients is discernible are levels in excess of about 250 μg/m3 smoke (BS) (total suspended particulate (HV) equivalent above about 350 μg/m3) in the presence of sulfur dioxide of about 500 μg/m3 (all as 24-hour average values). At these levels of particulate pollution, the effects on health are difficult, if not impossible, to disentangle from the health effects of temperature or other weather factors.