生物质燃烧排放PM2.5中无机离子及有机组分的分布特征

为探讨生物质在明火和阴燃两种不同条件下PM_(2.5)及主要成分的排放差异,选取了7种具有代表性的生物质样品(小麦、水稻、马尾松叶、马尾松枝、杂草、玉米、棉花)进行了燃烧实验,并对PM_(2.5)样品中的7种主要水溶性离子(Na~+、NH_4~+、K~+、Ca~(2+)、Cl~-、NO_3~-、SO_4~(2-))及有机碳(OC)、元素碳(EC)、水溶性有机碳(WSOC)、有机酸和左旋葡聚糖(LG)等有机成分进行了分析.结果表明,明火和阴燃条件下PM_(2.5)的排放因子分别为2.82~7.74 mg·g~(-1)和3.24~22.56 mg·g~(-1),阴燃时的排放因子偏高,不同燃料类型也存在一定差异.燃烧排放PM_(2.5)中水溶性离子以Cl~-为最高,占总离子的比例为72%~94%,且与NH_4~+存在显著正相关关系,水溶性离子整体表现为明火条件下的浓度显著高于阴燃条件下的浓度.受阴燃条件下氧气不足的影响,PM_(2.5)中有机组分的浓度表现为阴燃高于明火,进而导致阴燃时PM_(2.5)的排放因子增加.水稻秸秆燃烧烟尘中3种来源特征比值(LG/PM_(2.5)、LG/OC和LG/WSOC)仅为小麦和玉米秸秆燃烧排放相应比值均值的0.34、0.24和0.27倍,表明在不同农作物的收获季节采用上述特征比值进行生物质燃烧来源估算时,应区别对待.

Characteristics of inorganic ions and organic components in PM2.5 from biomass burning

Seven kinds of biomass samples including masson pine needles and branches, wheat, rice, grass, maize and cotton straw were burned under flaming and smoldering conditions to investigate the emission factors of PM_2.5 and its associated major components including organic carbon (OC), elemental carbon, water soluble ions, water soluble organ carbon (WSOC), organic acids and levoglucosan (LG). The results showed that the emission factors were in the range of 2.82~7.74 mg·g^-1 and 3.24~22.56 mg·g^-1 for PM_2.5 from biomass burning in flaming and smoldering conditions, respectively. The difference between the two burning conditions varied in different kinds of biomass fuel. The profiles of water soluble ions in PM_2.5 were all dominated by Cl^-, accounting for 72%~94% of the total water soluble ions. Significant positive correlations were only observed between Cl^- and NH₄⁺. The concentrations of water soluble ions were generally higher in flaming PM_2.5 than those in smoldering PM_2.5. The organic components showed much higher levels in smoldering PM_2.5 with respect to those in flaming PM_2.5 because of incomplete burning. The higher emission factors of PM_2.5 under smoldering conditions were mainly due to the higher emission factors of organic species. Three source characteristic ratios including LG/PM_2.5, LG/OC and LG/WSOC in rice straw burning PM_2.5 were only 0.34, 0.24 and 0.27 times of the mean ratios in wheat and maize straw burning PM_2.5, respectively. Thus, different characteristic ratios are required to estimate biomass burning contribution in different biomass burning seasons.