The effect of SO2 on NO removal by Ca(OH)2 was investigated at a low temperature. The influence of H2O and O2 on the enhancement effect of SO2 on NO removal was analyzed. The experimental results showed that NO removal was negligible in the absence of SO2. SO2 could enhance NO removal. H2O and O2 have great influence on the enhancement of SO2 on NO removal. NO could not be absorbed by Ca(OH)2 in the absence of O2

even though a high SO2  removal could be attained. SO2 could enhance NO removal when H2O and O2 were present in the flue gas simultaneously. CaSO3

a typical desulfurization reaction product

could not oxidize NO to NO2. The multi-molecular intermediate species

which could decompose to NO2

was not formed from the adsorption of NO

H2O and O2 on the surface of absorbent. There may be some unstable intermediate species formed from the desulfurization reaction

which can accelerate the reaction of NO and O2.