The main objectives are to explore the possible SO_2 conversion reactions under the condition of calcium chloride absorption method( CCAM) and the effects of these reactions on SO_3 measurement by the CCAM. The vertical-horizontal tube furnace and variable-controlling approach were used to study the influences of water vapor,oxygen atmosphere,temperature,reactant concentration on the chemical reaction between SO_2 and CaCl_2. On this basis,the possible chemical reaction mechanisms of SO_2 and CaCl_2 and the...