Characterization of pollutants emitted during burning of eight main tree species in subtropical China

Abstract

Understanding the chemical composition of pollutants released from forest fuel burning is crucial for revealing the effects of forest fire on the atmosphere and ecosystem. However, relevant studies exploring this aspect in China are rare. The emission factors (EFs) of five key pollutants (CO, CO2, NOx, PM2.5), non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) from different components of eight dominant tree species in sub-tropical China were determined under both smoldering and flaming stages using a self-designed combustion system. Results demonstrate that the emissions factors of different pollutants varied by tree component under both combustion stages. The average EFs of gaseous pollutants and PM2.5 of leaves, branches, and bark from the eight tree species under two combustion stages equaled 230.49 ± 17.61 (smoldering) vs. 154.35 ± 15.61 (flaming, g/kg) for CO; 1018.23 ± 48.77 vs. 1307.86 ± 76.99 (g/kg) for CO2; 1.16 ± 0.16 vs. 1.42 ± 0.23 (g/kg) for NOx; and 18.62 ± 4.30 vs. 9.51 ± 2.75 (g/kg) for PM2.5. Under different combustion stages, leaves and branches from these different tree species released 48 types of NMHCs, including 19 alkanes, 15 alkenes, and 14 aromatic compounds. The total EF of NMHCs ranged from 841.35 to 1846.46 mg/kg (smoldering) to 754.32–1128.88 mg/kg (flaming) for leaves, and from 539.50 to 2907.14 mg/kg (smoldering) to 698.11–1013.49 mg/kg (flaming) for branches. The NMHCs released from the combustion of leaves and branches under smoldering stage were more harmful to the environment and human health than flaming stage, with the most threatening NMHCs released by forest fires being alkenes and i-butane, 1-butene, 1,3-butadiene, benzene, and p-xylene. Acetic acid was found to be the most abundant species among OVOCs, followed by Glycolaldehyde, Formaldehyde, Phenol, and Furan. Our findings are an important step towards further understanding the ecological and health implications of forest fires in subtropical China.