The main objectives are to explore the possible SO2 conversion reactions under the condition of calcium chloride absorption method (CCAM) and the effects of these reactions on SO3 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 SO2 and CaCl2. On this basis

the possible chemical reaction mechanisms of SO2 and CaCl2 and the effects on SO3 measurement were analyzed theoretically. The results showed that SO2 could not undergo the homogeneous reactions in the absence of CaCl2. Under typical conditions of CCAM

only when H2O and O2 existed simultaneously

an obvious chemical reaction between SO2and CaCl2could occur. The conversion rate of SO2 can be improved with the increase of temperature and reactant concentration and the conversion rate is 2% to 8% approximately. Finally

the theoretical analysis demonstrated that the heterogeneous reaction was extremely week at 200 ℃and under typical sampling atmosphere

and this reaction was severely inhibited in the presence of high concentration of gaseous H2SO4. Therefore

the effect of SO2 interference on SO3 measurement could be ignored

which proved the feasibility of the CCAM to some extent.