Technical Report No. 5
J. Gras, C.Meyer, I. Weeks, R. Gillett, I. Galbally, J. Todd, F. Carnovale, R. Joynt, A. Hinwood, H. Berko and S. Brown.
Environment Australia, March 2002
ISBN 0 6425 4867 6
5. Use of aerosol mass emission factor, from AS4013 compliance testing as a surrogate for other toxic emissions
Within Australia, the emphasis for compliance testing of residential wood combustion appliances has been on the regulation of aerosol (particulate) emissions. Internationally, the approach is mixed with some jurisdictions emphasising particle mass emissions (e.g. USA, Canada) and others, for example, regulating CO, or VOCs. How well the current Australian standards capture these other constituents is, so far, an unanswered question. In the review Technical Report No. 4: Review of Literature on Residential Firewood Use, Wood-Smoke and Air Toxics, results of previous Australian work are discussed, showing no correlation between the aerosol and CO mass emission factors although other studies, such as Cianciarelli and Morcos (2000) have shown limited correlations. In the present study a clear functional, but non-linear, relationship between CO and aerosol mass emission factors is apparent (Fig. 28). Correlation between these two parameters is reasonably strong with r2 = 0.46. Since a large part of the aerosol mass results from condensation of organic compounds, a reasonably strong relationship between unspeciated VOC and aerosol mass emission factors should be expected and is observed (Fig. 29). The functional form appears to be non-linear although the relationship is quite strong (r2 = 0.55). Correlation with aerosol mass emissions varies for individual species, for example benzene r2 = 0.31, ethylbenzene r2 = 0.32, chloromethane r2 = 0.38, toluene r2 = 0.55 and xylenes r2 = 0.58.
For both CO and unspeciated VOCs there is clearly a tendency for 'clean' burns, based on aerosol mass emissions to produce lower concentrations. This is also true for many aerosol species. There are notable exceptions however. Examples include PCDD/F, which have already been discussed, where the need to minimise residence time in the 300–450 °C temperature zone appears counter to the requirements for reducing mass emissions in general. See for example Fig. 22. It is also evident, for example from Fig. 30, that production of nitrogen oxides is greater for burning conditions where the aerosol mass emissions are lower and vice versa. In the case of NOX, direct correlation with aerosol mass is weaker, yielding r2 = 0.21.
PAH emissions overall do not correlate particularly well with aerosol mass emissions (overall r2 = 0.24), but there is a clear trend for the higher PAH emissions to occur with higher mass emissions whilst high mass emissions may be associated with low PAH emissions (Fig. 31). Other species show varying degrees of correlation with aerosol mass emissions, for example aldehydes, where formaldehyde didn't correlate very strongly, giving only r2 = 0.09 whilst for acrolein r2 = 0.58. Aldehydes are generally emitted at temperatures greater than 450 °C (Ballard-Tremeer 1997). In the ketone group, methyl isobutyl ketone (MIBK) and aerosol mass were well correlated with r2 = 0.58 for all fuels and r2 = 0.46 for eucalypts. 2-Butanone, another ketone (also known as methyl ethyl ketone or MEK), was observed only in a small subset of eucalypt burns and did not correlate with aerosol mass emissions. For SO2 and all fuels the correlation with aerosol mass emission was relatively weak with r2 = 0.17, although the burns from green pine tended to produce lower SO2 emissions compared to the general group and deleting those burns gave r2 = 0.28.
Overall, it can be concluded that control of aerosol mass emissions through AS4013 would bring about a concomitant control of the emissions of most of the species considered, albeit for some species, for example PAH and SO2, the relationships with mass are weak. There were two clear exceptions; one was nitrogen oxides, the other dioxins. In both cases it appears that heater design or operation parameters that tend to reduce the aerosol mass emissions work to increase the emissions of these species.