Acidic impurities in the flue gas, such as SO2 and NOx, are supposed to promote amine degradation in the amine scrubbing process for CO2 capture. This work investigates the effect of these acidic gases on thermal degradation of MEA (monoethanolamine) by preloading additives, which are Na2SO3, SO2, H2SO4, and HNO3, respectively. MEA concentration was 4.4 mol/kg. CO2 loading was 0.4 mol/(mol of MEA). Experiment temperature varied from 120 to 150 degrees C. Ion chromatography (IC) is the main analytical method. The results show that the MEA thermal degradation rate was not affected by these additives. Ammonium became an important product in the experiment with SO2 or HNO3 loading. Sulfate was stable in the experiment. In the experiment with SO2 loading, most of the sulfur remained dissolved in the solution after degradation but could not be detected by IC. A lower pH value will speed up sulfite degradation.