关键词: 杉木, 枯落物, 燃烧状态, 排放特征, PM_2.5

Abstract: [Objective] The objective of this study was to investigate the emission characteristics of gaseous and particulate pollutants from litterfall of Chinese fir plantation under different combustion states, and to extract and determine the chemical composition of PM_2.5, in order to reveal the impact of forest fire and forest clearing on litterfall decomposition, nutrient cycling, and atmosphere environment.[Method] Four main components of leaves, branches, barks and stems of litterfall in Chinese fir plantation were selected as research materials. With a self-designed biomass simulation combustion system, an indoor simulation combustion experiment was conducted to analyze the characteristic variation of gaseous pollutants and PM_2.5 released by different litter components under smoldering and flaming states. The carbonaceous components in PM_2.5 were determined by an Elementar elemental analyzer (produced in Germany). The contents of water-soluble ions and water-soluble inorganic elements in PM_2.5 were identified by ultrasonic extraction-ion chromatography and ICP/MS techniques.[Result] The result showed that the emission factors of CO₂, CO, NO_x, C_xH_y and PM_2.5 varied in the range of 1 001.4-1 364.5,202.3-358.8, 0.53-3.09, 23.17-53.07 and 5.11-38.37 g·kg^-1 in the smoldering state, respectively and varied in the range of 1 092.4-1 520.7, 115.1-242.6, 0.16-1.961,1.21-41.50, 2.58-21.07 g·kg^-1 in the flaming state. In addition, the components of PM_2.5 were extracted and determined. The result showed that PM_2.5 contained carbonaceous components, water-soluble ions and a small amount of water-soluble inorganic elements. The content of carbonaceous components occupied the largest proportion, accounting for more than 50% of PM_2.5. The average mass fractions of organic carbon (OC) and elemental carbon (EC) were 43.29% and 12.91% respectively. Six cations (Li⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, and Ca²⁺) and five anions (F^-, Cl^-, NO^2-, SO₄^2- and NO₃^-) were identified in PM_2.5, and the total water-soluble ions accounted for 10% -33% of PM_2.5. Cl^-, K⁺, Ca²⁺, and SO₄^2- were determined as main water-soluble ions in smoldering state and K⁺, Cl^-, SO₄^2-, and Na⁺ were main water-soluble ions in flaming stage. Sixteen inorganic elements (K, Ca, Na, Mg, P, Zn, Al, Cu, As, Ba, Cr, Fe, Mn, Cd, Li and Pb) were extracted from PM_2.5, but accounting for only 0.04%-0.58% of PM_2.5, of which K, Ca, Na, Mg, P and Zn were the main elements, accounting for 96.8% to 98.8% of the total inorganic elements.[Conclusion] The same litterfall type under different combustion states showed significant differences in the emission factors of pollutants. Except CO₂, the emissions of other pollutants in smoldering state were significantly higher than those in flaming state. In addition, there existed significant variation exists in the emission factors of CO, CO₂, NO_x, C_xH_y and PM_2.5 from different components of litterfall of Chinese fir plantation at the same combustion state. PM_2.5 was mainly composed of carbonaceous components, water-soluble ions and a small amount of inorganic elements and other ingredients. Generally, the concentration of each component in PM_2.5 in the smoldering state was higher than that in the flaming state.

Key words: Chinese fir, litterfall, combustion state, emission characteristics, PM_2.5