Comparison of Air Pollution Caused By Cars and Woodheaters

In Armidale wood heaters are almost certainly the source, not just of health hazardous fine particle pollution, but all major air pollutants. Contrast, for example, the amount of pollutants from travel to work with those from wood heaters. Local council data show that about 47% of residential properties have wood heaters and a further 8% have open fires. In Sydney, 13% of households using wood in Sydney contribute 2/3rds to 3/4 of all particulate air pollution. In Armidale, a small town with substantially less traffic but much higher wood heater useage, virtually all air pollution is caused by wood heating. This is confirmed by the fact that in summer, when wood heaters are not in use, measured pollution is almost zero.

By contrasting emission rates for, eg, car journeys to work with wood heaters, we can see that woodheaters are the source not just of fine particle pollution, but all the major air pollutants.

Census data for 1991 show there were approximately 4230 car journeys to work in Armidale. Car emissions standards in 1986 were 9.3 g/km for CO and 1.93 g/km NOx. (The new standard ADR 37/1, which comes into force in 1997 will limit emissions of CO to 2.1 g/km and NOx to 0.63 g/km for new car models, a huge reduction.) Many current models also on sale in the US are likely to satisfy the new standard, but assuming the 1896 standard represents the fleet average, for an average journeys to work of 10 km (Armidale is a small town!), total emissions would be 4,230 x 10 x 9.3 = 393 kg CO and 82 kg NOx.

This compares with approximately 17,000 tonnes of firewood burned each year, or 113 tonnes per day during the heating season *. Wood heaters average 130 kg of CO and 1.4 kg of NOx per tonne burned,** so daily emissions from wood heaters amount to 14733 kg of CO and 159 kg NOx and, 35 and 1.9 times the pollution from travelling to work! Note that the new woodheater standard AS4013 deals only with particulate pollution. There is no reqirement for new wood heaters to produce less CO or NOx or carcinogenic PAHs (poly-cyclic aromatic hydrocarbons eg as benzo(a)pyrene) than existing ones.

* Proceedings Armidale City Air Quality Workshop, Armidale City Council/EPA July 1995.

** Table 5.17. Air emission inventories (1985) for the Australian Capital Cities. Australian Environment Council Report No 22, Aust. Govt. Publishing Service, 1988.