树木模拟燃烧排放烟尘中水溶性离子的组成

模拟林火中生物质的两种燃烧方式,明燃和闷燃,对10种乔木的干树枝和绿树枝进行室内燃烧试验,测定了排放烟尘中的水溶性离子.结果表明,干树枝明燃烟尘中水溶性离子的平均总含量为(28.88±17.54)g·kg~(-1).SO_4~(2-)、Cl~-、K~+是主要组分,其平均排放因子为101.0~118.2 mg·kg~(-1).干树枝闷烧烟尘中水溶性离子的平均总含量为(6.38±2.79)g·kg~(-1).Na~+、SO_4~(2-)、K~+、Cl~-是主要组分,其平均排放因子为101.1~245.7 mg·kg~(-1).绿树枝明燃烟尘中水溶性离子的平均总含量为(22.13±13.52)g·kg~(-1).SO_4~(2-)、Cl~-、K~+是主要组分,其平均排放因子为136.4~197.6 mg·kg~(-1).绿树枝闷燃烟尘中水溶性离子的平均总含量为(15.71±19.09)g·kg~(-1).Cl~-、SO_4~(2-)、Na~+是主要成分,其平均排放因子为298.6~869.1 mg·kg~(-1).两类树枝在每种燃烧条件下产生的烟尘中,Cl~-与K~+的含量均显著正相关.干树枝闷烧时Cl~-的排放因子与含水率显著正相关.燃烧条件、树种及含水率均对森林生物质烟尘中水溶性离子的组成及排放因子有明显的影响.这对估算大气中林火来源的污染物有参考意义.

Chemical Composition of Water-soluble Ions in Smoke Emitted from Tree Branch Combustion

Water-soluble ions in particulate matter (PM) from tree branch combustion were determined. The results showed that the average content of total water-soluble ions in flaming PM from dry branches was (28.88±17.54) g·kg^-1. The major components included Cl^-, SO₄^2-, and K⁺, the mean emission factors (EFs) of which were in the range of 101.0 to 118.2 mg·kg^-1. In addition, the mean content of the total ions in smoldering PM was (6.38±2.79) g·kg^-1. The main constituents contained Na⁺, SO₄^2-, K⁺, and Cl^-, the mean EFs of which varied from 101.1 to 245.7 mg·kg^-1. The average content of the total ions in flaming PM from green branches was (22.13±13.52) g·kg^-1. Their major components were SO₄^2-, Cl^-, and K⁺, with mean EFs ranging from 136.4 to 197.6 mg·kg^-1. Furthermore, the mean content of all ions in smoldering PM derived from green branches was (15.71±19.09) g·kg^-1. Cl^-, SO₄^2-, and Na⁺ were the main components, with mean EFs varying from 298.6 to 869.1 mg·kg^-1. Significant correlations were found between the contents of Cl^- and K⁺ in PM from dry and (or) green branches burned under each condition. Similar relation also existed between EFs of Cl^- from the dry branches burned in smoldering condition and the moisture in them. The EFs of Cl^-, K⁺, and Mg²⁺ were positively correlated with moisture while the green branches were burned in flaming condition. The EFs of Cl^-, Na⁺, NH₄⁺, and Mg²⁺ were significantly positively correlated with moisture as well when the fuels were combusted in smoldering condition. Combustion conditions, tree types, and moisture in wood fuels all had impacts on the chemical compositions and EFs of water-soluble ions in PM from tree branches. This may have significance in estimating the quantity of the pollutants from forest fires.