Estimation of Metal Emissions From Tropical Peatland Burning in Indonesia by Controlled Laboratory Experiments

The tropical peatland burning in Indonesia is one of the most significant types of wildfires on a global scale. Previous studies indicated the importance of metal emissions from Indonesian wildfires. However, metal emission profiles from Indonesian wildfires have not been quantified well yet. To address this issue, we analyzed metals and metalloids emitted from combustion experiments of peat and vegetation growing over peatland in Indonesia. The analyzed elements include Mg, Al, Ca, V, Cr, Fe, Co, Ni, Cu, Zn, Se, Sn, and Pb. The emission ratios of aerosol particles emitted from combustion of the ombrotrophic peat and vegetation agreed within a factor of few, regardless of the variability in the elemental compositions of the original fuel. In both cases, the emission ratios of Ca were the highest, followed by crustal elements Fe and Al. The concentration ratios of crustal and biogenic elements (Fe/Al and Zn/Fe) were found to be a useful metric to infer dominant fuel types. Namely, the concentration ratio of Fe/Al was high (6.2 ± 4.4) for peat combustion particles, while the value was lower (1.9 ± 1.3) when plant burning was conducted. The emission ratios of the metals were combined with an existing emission inventory to estimate the emission rates of the analyzed metals. The emission rates of carcinogenic metals, such as Cr and Ni, were estimated to be 0.02 and 0.013 Gg/year, respectively. The analysis also indicated that the peatland burning could be one of the important sources of atmospheric Fe in the region.