Abstract: Exploring the element contents and their correlation between forest fuel and fine particulate matter (PM_2.5) emitted during combustion and revealing the migration trajectory of each element during forest fire provide an important basis for understanding the impacts of forest fire on environmental chemical element content and ecosystem material cycle. The branches, leaves and bark of four tree species (Pinus massoniana, Cunninghamia lanceolata, Eucalyptus robusta and Cinnamomum  camphora) were burnt under smoldering and flaming states using self-designed combustion simulation device to measure the contents of five major elements (Mg, Al, P, K, Ca) and seven trace elements (Na, Cr, Mn, Fe, Ni, Cu, Zn). We analyzed the differences of element contents in PM_2.5 emitted between different burning states, and the correlation between the element contents of fuels and the emission factors of each element in emitted PM_2.5. The results showed that the contents of Mg, K, Ca and Zn in forest fuel were higher. The element contents in conifers were generally higher than those in broadleaved species, and the element contents in different organs of same tree species were significantly different. The emission factors of Mg, K, Ca and Zn in PM_2.5 released during combustion were highest, followed by Cu and Cr, with a pattern of higher for the major elements than for the trace elements. Combustion states influenced emission factors of elements, generally showing that flaming was greater than smoldering. Under different combustion states, the ratio of Cu content in PM_2.5 released during combustion of each organ to its own element content was the highest, and the ratios of other elements ranged from 0 to 0.09%. The correlations of element contents between forest fuels and PM_2.5 were relatively high (0.700-0.999). In conclusion, there were differences in emissions of flue gas and PM_2.5 released by the combustion among different tree organs, and there was a strong correlation between fuel itself and PM_2.5 released by fuel combustion.

Key words: forest fuel, PM_2.5, combustion state, forest fire