EMISSION FACTORS FOR PCDD/PCDF FROM FOREST AND CROP FIRES – REVISION OF CATEGORY 6a OF THE UNEP TOOLKIT

Black R1, Meyer C2, Touati A3, Gullett BK4, Fiedler H5, Mueller, JF1 1The University of Queensland, National Research Centre for Environmental Toxicology (Entox) 39 Kessels Rd, Coopers Plains, QLD 4108 Australia; 2CSIRO Atmospheric Research, Aspendale, Vic, Australia; 3ARCADIS Geraghty and Miller, Inc, PO Box 13109, Research Triangle Park, North Carolina 27709, USA; 4 National Risk Management Research Laboratory, US Environment Protection Agency, (E343-04), Research Triangle Park, North Carolina 27711, USA; 5 UNEP Chemicals Branch, chemin des Anémones 11-13, CH-1219 Châtelaine (GE), Switzerland. Introduction The Stockholm Convention on Persistent Organic Pollutants (POPs) aims to reduce, and where feasible, eliminate the releases of unintentional POPs, such as polychlorinated dibenzodioxins/dibenzofurans (PCDD/PCDF), with the aim of protecting human health and the environment from these chemicals. In order to achieve this, parties are required to identify sources of release, develop, and maintain release inventories of unintentional POPs. To assist with this process, in 2001, the United Nations Environment Progamme (UNEP) developed a Toolkit that provides a methodology to identify sources of PCDD/PCDF and to quantify their releases. The Conference of the Parties to the Stockholm Convention in its decision SC-2/5 on the ongoing review and updating of the “Standardized Toolkit for Identification and Quantification of Dioxin and Furan Releases”, requested the Secretariat “to initiate an open, transparent process, in cooperation with the Chemicals Branch of the United Nations Environment Programme’s Division of Technology, Industry and Economics and in consultation with users and specialized experts in the field of emission factors and measurements related to releases of Annex C persistent organic pollutants, to further develop the Toolkit[1]. In order to do so, a Toolkit Expert Group [2] has been established that works intersessionally and meets annually. Using this Toolkit, to date about 60 national emission inventories have been developed and submitted to UNEP as part of the National Implementation Plan, national reporting or published elsewhere. One category of the Toolkit (sub-category 6a) concerns open combustion of biomass. The submitted data to date suggests, depending on the activity in a given country, that biomass combustion (Cat 6a) contributes between 0.5 % and 68 % to total PCDD/PCDF emissions (reported as toxic equivalents, TEQ). In 2001, at the time of the release of the first Toolkit, and even for the 2nd version in 2005, only few data on emission factors (EFs) were available; hence the uncertainties associated with the emission factors provided in the UNEP Toolkit were large. This resulted in a number of studies that aimed at determining emission factors for dioxin-like chemicals. Work at the US EPA was carried out in specifically designed burn facilities [3-6] where the emissions were measured in semi-controlled systems. In France [7] a combustion chamber was used to measure emissions taking into account national circumstances. Alternatively, field experiments using a mobile sampling unit with on-line CO2 measurement and VOC sampling was the method of choice for determining EFs in more than 50 experiments carried out in Australia [8-11]. In total, more than 105 experiments were carried out through the last decade using five different fuel types and three main methodologies. Discrepancies between emission factors using different methodologies were addressed in a UNEP-funded study where the main methodologies were applied to measure emission factors from the same fuels [12]. The aim of this paper is to

a) Review and summarise the available data on emission factors for PCDD/PCDF from forest and agricultural fires; and

b) Present and rationalize the new PCDD/PCDF EFs proposed for the revised UNEP Toolkit sub-category 6(a).

Approach and data gathering The approach for this work was to obtain emission factor estimates from the literature, including the recent study obtained from a methodology comparison study for determination of emission factors carried out jointly by the authors of this paper. In brief, emission factors for chemicals such as PCDD/PCDF are derived either from mass balance type studies or more routinely by measuring the amount of CO2 entering the sampler, then subtracting the background CO2 and attributing the remaining CO2 to the combustion process. Assuming this is a representative sample of the carbon and dioxin-like chemicals emitted from the combustion process, this approach is valid for both field sampling and combustion room tests (for details, see Meyer et al. 2004). For this study we collated data from seven studies that reported PCDD/PCDF emission factors related to combustion of wood simulating forest fires, sugarcane, cereal crops and grass/savanna. The studies considered are listed in Table 1. Since many of the studies expressed results on a g-carbon basis and others on g-fuel burned, for uniformity, all data was converted to µg TEQ (t fuel)-1. The EF per ton fuel is obtained by dividing carbon based results by factor 2, since fuel is approximately 50 % carbon. These units are used in the Toolkit and throughout this paper Table 1: The studies that have been considered in the revised Toolkit.

Authors Type Fuel (No values reported)

Brief summary of the study and problems reported

Gullett et al. 2003a OBTF FO (2) Live shoot and litter biomass from North Carolina and Oregon forests, U.S.A.

Gullett et al. 2003b OBTF CC (7) Cereal crops (wheat and rice), U.S.A. Meyer et al. 2004* IF FO (14)

SC (2) GR (4)

In field burns with a mobile sampler. Covered sampling across much of Australia. Also undertook laboratory studies using the same material but identified formation in the lab study as an artifact. Lab data not included.

Collet and Fiani (2006)

OBTF FO (5) Little information available for this study from France. Tested effects of additional chlorine (administered through seawater) on EF.

Gullett and Touati (2006)

OBTF SC (6) Burned cane from Hawaii and Florida and found significantly higher emissions from Hawaiian sugarcane (mean > 100 µg TEQ/ton).

Meyer et al. 2009 IF OBTF

FO,GR,CC (13)

In field burns with mobile sampler, Australian forest, sorghum and grass

Black et al. submitted OBTF IF OB

FO, SC GR (26)

In field burns with mobile sampler, and burn test facility, sugarcane from Florida, forest in North Carolina

Types: OBTF- open burn test facility; OB – open semi controlled on bricks; IF – in field Fuel: FO – Forest incl. conifers and deciduous; SC – Sugarcane; GR – Grass/Savanna; CC – Cereal crops *Meyer et al. (2004) also conducted a number of lab burns, but identified artifacts, and these results are not included Results and Discussion In the global data set, biomass emission factors to air vary over a 100-fold range. Statistics for emissions grouped by experimental sampling technique are shown in Figure 1A and by biomass type are shown in Figure 1B. Median

emission factors to air (EFAir) are 0.86 µg TEQ (t fuel)-1, 0.24 µg TEQ (t fuel)-1, 0.5 µg TEQ (t fuel)-1, and 1.2 µg TEQ (t fuel)-1 for forest, grassland/savanna, cereal crops, and sugarcane, respectively.

Figure 1 Summary of the current global data set of EFAir for PCDD/PCDF for open burning. A: Stratified by measurement system; B: stratified by biomass type Based on these data, recommendations were made to the Toolkit Expert Group for revision of category 6a emission factors taking into account the general advice that structure of the classes in the Toolkit should be maintained as much as possible, to make updating of inventories manageable. Based on the number of studies, the relevance of sugarcane burns and the new results, it was recommended to expand and detail the emission factors by introducing additional/separate emission factors for sugarcane and cereal crop. While the authors recognized that emission factors will vary depending on factors such as fuel origin and composition as well as combustion conditions, the authors proposed one aggregated emission factor for each fuel or condition. The EFs are presented in Table 2.

Applying these new emission factors to national data, for example Argentina, results in a revised estimate of the annual emissions of dioxin-like chemicals to air due to open burning of 350 g TEQ per annum. Importantly this changes the estimated contribution of open burning of biomass to the total national PCDD/PCDF emissions, from over 75 % to about 40 % when all other activities and emission factors remain unchanged. Table 2 Current and proposed new emission factors and reorganization of classes for the UNEP Toolkit Category 6a

Classification

Current Proposed Emission to air

(ug TEQ/t material burned)

Emission to land (ug TEQ/t of

material burned)

Emission to air (ug TEQ/t material burned)

Emission to land (ug TEQ/t of

material burned)

Agricultural residue burning (in the field), impacted, poor conditions

30 10 N/A N/A

Agriculture residue burning (in the field), not impacted

0.5 10 N/A N/A

Sugar Cane Burning - - 4 0.05 Cereal crop - - 0.5 0.05 Forest Fires 5 4 1 0.15 Grassland & Savannah 5 4 0.5 0.15

Conclusions The new set of EFs to air and land were proposed to the Toolkit Expert Group, who discussed and confirmed the proposed values to be sound and recommended the new EFs for inclusion in the next version of the Toolkit.  References 1. Stockholm, Convention meeting.,

<http://chm.pops.int/Secretariat/SecondCOPmeeting/tabid/288/mctl/ViewDetails/EventModID/870/EventID/3/xmid/953/language/en-US/Default.aspx#LiveContent[COP2report>], 2007.

2. Toolkit Expert Group meeting, http://www.chem.unep.ch/Pops/pcdd_activities/toolkit%20experts%20meetings/default.htm

3. Gullett, B. and A. Touati,. Atmos Envir, 2003. 37(35): 4893-4899. 4. Gullett, B., A. Touati, and L. Oudejans, Atmos Envir, 2008. 42(34): 7997-8006. 5. Gullett, B.K. and A. Touati, Atmos Envir, 2003. 37(6): 803-813. 6. Gullett, B.K. and A. Touati, Environ Sci & Tech, 2006. 40(20): 6228-6234. 7. Collet, S. and E. Fiani, Organohalogen Compd, 2006. 68: 856-859. 8. Meyer, C., Mueller, J.F., Symons, R.K., 2009. http://www.cmar.csiro.au/e-print/open/2009/meyercp_a.pdf 9. Meyer, C., T. Beer, and J. Mueller, Technical report No 1 Dioxin Emissions from Bushfires in Australia.

2004. 10. Meyer, C., Black, RR., Beer, T., and Mueller, JF., Organohalogen Compd, 2007. 69(2007): 307-310. 11. Meyer, C.M., et al., Organohalogen Compd,. 66: (2004) 928-934. 12. Black, RR., Meyer, C., A. Touati., Gullett, BK., Fiedler, H., and Mueller JF. submitted Chemosphere, 2010.