Release of Organochlorine Pollutants from Forest Fires: 1. Emission Factors and Revisiting Their Emissions in the Himalayan Regions

Worldwide forest fires have occurred frequently in recent years, a result of which may be the emission of so-called "legacy" organochlorine pollutants (OCPs) accumulated in forests. However, few studies have measured the emission factors (EFs) of the toxicity of the OCPs from forest fires. In this study, the EFs of vegetation burning were observed in forests along the altitudinal gradient from 1000 to 4200 m, and the EFs of ∑DDTs (dechlorodiphenylthrichloroethanes), HCB (hexachlorobenzene), ∑HCHs (hexachlorocyclohexanes), and ∑PCBs (polychlorinated biphenyls) were 2050 ± 1175, 379 ± 409, 48 ± 51, and 65 ± 59 ng/kg, respectively. Re-evaporation was the primary mechanism of the emission of OCP from forest fires. The masses of HCB, β-HCH, o,p'-DDD, p,p'-DDD, and PCB-28 in smoke increased 3-7 times compared with those in unburnt vegetation, suggesting the formation of these pollutants by the pyrolysis of biomass or other pollutants. Based on the observed EFs, previously estimated quantities of fire-emitted OCPs in the Himalayan regions were revisited. The DDT emissions from the Himalayan forest fires increased ∼70% compared with the previous estimation (from 19 to 32 kg/year). This highlighted that the EF observations could decrease the uncertainties of estimating OCP emissions from forest fires, which is helpful in revealing the potential roles of forest fires on global POP cycling.