Annex 45 Complementary information to source category 6a Biomass Burning

Overview of recent revisions

Since the last edition of the Toolkit (2nd version from 2005), new information has become available from several projects that have been implemented to provide emission factors for the open burning of different types of biomass. Especially one project commissioned by the Secretariat of the Stockholm Convention and implemented by UNEP Chemicals Branch improved the measurement techniques by running the same samples in open burn hut and field sampling methods; i.e., the US-EPA Open Burn-hut Facility and the Australian “whoozle” technique by EnTox and CSIRO (Black et al. 2011a, UNEP 2011b). The same project also assessed all measured data and recommended an improved classification scheme and new emission factors for PCDD/PCDF. Suggested improvements included a new emission class, sugarcane burning, and substantial revisions to emission factors to land (Black et al. 2011b). Because better simulations or even field studies are available now, the older references have been removed from this section and replaced by the more recent studies. The revised emission factors for PCDD/PCDF are presented in Table II.6.3 and emission factors for dioxin-like PCB are given below:

Table III.45.1 Dioxin-like PCB emission factors for source category 6a Biomass Burning

6a Biomass Burning Emission Factors (µg TEQ/t biomass burned)
  Classification Air Water Land Product Residue
1 Agricultural residue burning in the field, impacted poor burning conditions 3*   0.3*    
2 Agricultural residue burning in the field, not impacted 0.05   0.01    
3 Sugarcane burning 0.05   0.01    
4 Forest fires 0.1   0.1    
5 Grassland and savannah fires 0.03   0.03    

* Based on expert judgment and analogy to PCDD/PCDF data

Derivation of emission factors

PCDD/PCDF formation and release from open burning of biomass vary considerably depending on the biomass itself and the conditions under which it is burned, e.g., the nature and composition of the forest, grassland, savannah, crop or residue, moisture content, the presence of contaminants, such as pesticides or salt water residues.

Due the lack of containment of ashes from open burning of biomass, the EFLand is given rather than EFResidue, since the ashes are most often left on land or incorporated into the soil.

Release to Air

For class 1 and 2, Gullett et al. (2002) performed biomass burns in a steel barrel in an open burn simulation facility and determined emission factors for wheat straw (containing ~0.8% Cl for spring straw and 0.08% for winter straw), rice straw (containing 0.33% Cl),and stubble (0.33% Cl). The wheat straw EFAir ranged from 0.337 to 0.602 μg TEQ/t of straw burned and, the EFAir for rice straw was 0.537 μg TEQ/t of straw. In this study, as well as in a more detailed description given by Gullett and Touati (2003a), an EFAir of 0.5 ng TEQ/kg was regarded as appropriate for both residues. The authors specified that the spring wheat had been treated with non-chlorinated herbicides but gave no information on other residues.

For class 3, Meyer et al. (2004a, 2004b) reported an EFAir of 0.8 ng TEQ/kg for burning sugarcane in fields in Australia, which was about three times less than the EFAir determined in a facility intended to simulate open burning conditions. A laboratory burn facility was used to determine emission factors for sugarcane fires using sugarcane leaves and stalks (Gullett et al. 2006) with mean PCDD/PCDF emission factors of 126 µg TEQ/t of fuel (range 98-148 µg TEQ/t of fuel) (Hawaii) and 12 µg TEQ/t of fuel (range 5.5 -26 µg TEQ/t of fuel) (Florida 1) and 5 µg TEQ/t of fuel (range 0.13-1.72 µg TEQ/t of fuel) (Florida 2).

For forest fires (class 4), Black et al. (2011a, 2011b) derived EFAir for forest fuel (Duke Forest, North Carolina) of 0.52 (range: 0.40–0.79), 0.59 (range: 0.18–1.2) and 0.75 (range: 0.27–1.2) µg TEQ/t of fuel consumed for the in-field, over a brick hearth, and burn facility experiments, respectively. In Australia, an EFAir of 0.5 ng TEQ/kg was derived for forest fires (wildfires and prescribed burns) and an EFAir of 1.0 ng TEQ/kg for savannah fires (class 5). This project entailed measurements of PCDD/PCDF air emissions from 21 field burns and 19 laboratory tests (Meyer et al. 2004a, 2004b).

Forest fire simulations in an laboratory burn facility were used to estimate PCDD/PCDF emission factors of 19 µg TEQ/t of fuel (range 1-56 µg TEQ/t of fuel) for biomass from Oregon and North Carolina (Gullett and Touati 2003b). Further forest fire simulations (Gullett et al. 2008) produced PCDD/PCDF emission factors ranging from 0.15 µg TEQ/t of fuel to 13 µg TEQ/t of fuel from forest biomass collected from four regions in North Carolina.

Release to Water

No EFWater is given since no direct release to water is expected. It should be noted that rainfall may wash away ash particles and some of this may enter water courses with relevance to subsequent contamination of receiving waters including sediments.

Release to Land

PCDD/PCDF are expected to be present in residues, which may be left on land or incorporated into the field surface constituting a release to land. PCDD/PCDF may be expected to be present in the ashes from fires. In some cases, these ashes may be used for their mineral content in agriculture. Ash production from these fires will vary with the conditions and the nature of the material combusted.

For class 1 and 2, Zhang et al. (2011) derived an EFLand of 0.20 ng TEQ/kg for pesticide-contaminated corn straw and an EFLand of only 0.002 ng TEQ/kg for uncontaminated corn straw. The finding by Walsh (1994) of no increase in PCDD/PCDF concentrations in soil following controlled straw field burning tests in the United Kingdom suggests that PCDD/PCDF concentrations in the ash were very low. Support for a low EFLand for burning non-impacted agricultural residues can be drawn from the findings of studies related to forest fires. For example, results from experimental burning of leaf litter and soil by Prange et al. (2003) indicate that releases to air are far greater than releases in ash and soil.

For class 3, using a portable field sampler to measure PCDD/PCDF emissions from open burning of sugarcane, a brick hearth to eliminate potential soil effects, and a laboratory burn facility, Black et al. (2011) derived EFAir of 1.1 (range: 0.40–2.2), 1.5 (range: 0.84–2.2) and 1.7 (range: 0.34–4.4) µg TEQ/t fuel consumed for in-field, over a brick hearth, open field and burn facility experiments respectively.

Gullett et al. (2006) reported that simulated pre-harvest burning of sugarcane produced about 4% ash that had PCDD/PCDF concentrations of 0.004 to 1.22 ng TEQ/kg CInitial.

For forest, grassland and savannah fires, two previous studies and the current work provide data from which emission to land can be estimated. The average ash concentration of 1.1 ng TEQ/kg ash when combined with the appropriate burning efficiency yields emission factors to land of 0.05 µg TEQ/t for sugar cane and 0.15 µg TEQ/t fuel burned, which is more than 20-fold lower than the 2005 Toolkit emission factors.

Release in Products

No EFProduct is provided. No product is expected.

Release in Residues

No EFResidue is provided since residues are typically left in place so that any accompanying releases are assumed to be to land.