[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.