EMISSION OF DIOXINS FROM BUSH FIRES IN AUSTRALIA

Samples from the smoke plumes of 18 field fires across Australia were collected and analysed to assess PCDD/F/PCB emission rates. Emission rates were variable across all fire classes (prescribed, wildfire, and savanna) .. The measured emission factors for our forest fires (prescribed and wildfires) and savanna fires averaged 1± 0.5 pg TEQ (g C) which translates to approximately 0.5 ug TEQ t1. PCDDs contributed on average 70% of the emissions (expressed as TEQ), with PCDFs and PCBs contributing a further 20 and 10% respectively. Our results consistently show a congener pattern in which PCDD predominates over PCDF, and in which the higher chlorinated groups are more common than the less chlorinated groups. A major consequence of this congener pattern is relatively low toxicity when compared to emissions from other combustion sources. This data were consistent across 18 measurements at different sites across Australia. In 90% of these samples, the emission factor was less than 3.0 pg TEQ/ (g C) this is much lower than expected emissions based on literature values. The results suggest that the emission factors provided in the UNEP toolkit appear to overestimate emissions from bush fires in Australia.