How toxic are fine particles emitted from home fires in Christchurch, New Zealand?

AIMS: Fine particles (PM10) in the air in Christchurch have been estimated to be a considerable health hazard, and 9.1% of all deaths have been attributed to them. Concentrations often exceed the national standard. The particles come from wood-burning stoves and hydrocarbon-burning traffic and industry. This study asks whether the particles from these sources are equally toxic, and whether a standard based on concentration of particles is appropriate as a measure for devising regulatory controls to safeguard public health. METHODS: Recorded concentrations of PM10 in Christchurch are much higher in winter than in summer. Published estimates show that 25% of the summer PM10 comes from home fires, and 75% from traffic and industry. It has been estimated that in winter 80% comes from home fires. Other published estimates show that in summer PM10 is 5 to 10 times more toxic than in winter. In this article these estimates are used together to estimate of the relative toxicity of PM10 from home fires compared with PM10 from traffic and industry. RESULTS: The calculations imply that the PM10 from home fires is less toxic than the PM10 from traffic and industry, and despite its predominance as a component in the winter PM10 it may be relatively harmless. An alternative explanation is that toxicity varies seasonally for each kind of PM10. CONCLUSIONS: Reducing total PM10 by reducing the component which comes from home fires may not reduce the incidence of premature deaths from PM10 pollution.