Uncertainty should lead to moderation in regulations or they will be seen to be unreasonable. There is uncertainty in relation to air pollutants. The biological plausibility for harm is most consistently demonstrated in pathophysiological studies testing SO2, ozone, and NO2, but epidemiological studies assessing these three pollutants have also given variable results.

It is difficult to claim causality for the association of a small excess in mortality with increased levels of ambient PM10 because of the presence of other pollutants, the frequent association with cold weather which precipitates acute episodes in those with cardiac and respiratory disorders, and the fact that most studies do not reflect the important indoor environment. Given this, claims of a large estimated number of deaths caused by PM10 appear alarmist and a misapplication of the statistics.

The social and economic consequences of the current National Environmental Standards Regulations applying to all urban areas are broad. They may also have an influence on the redevelopment of Christchurch by focussing planning in relation to air pollution away from the important influences of industry and transport.

Currie and Hunt1 give very confident support to the PM10 theory. Their confidence is not shared by Paul Solomon,2 U.S. Environmental Protection Agency, Chair 2010 AAAR Air Pollution and Health Conference. “Although associations have been identified between pollutants....(CO, Lead, NO2 , PM2.5, PM10, ozone and SO2)....and adverse health effects, considerable uncertainty remains regarding....approaches to understanding relationships between air pollution and health effects....which components and sources are most toxic...the mechanisms of actions of the pollutants and causal relationships....This holds true especially for PM because it is composed of many components with significant spatial and temporal variation.”

Our government's efforts to improve domestic insulation are to be applauded. The enforced replacement of older wood burners with new ones may be an expense with little public benefit and conversion to electrical heating may reduce our energy security. Unfortunately the current regulations in relation to PM10 make these changes inevitable.

In relation to the causation of ill-health by PM10 questions concerning biological plausibility, the strength of the association and alternative explanations remain. As a consequence it must be doubtful whether the regulations are reasonable, their basis robust, and whether some of the costs which follow from them are justified.