The effect of gas-liquid phase compositions on NO and NO2 absorption into ammonium-sulfite and bisulfite solutions is investigated. Preliminary experiment results indicate that the concentrations of (NH4)(2)SO3 or NH4HSO3 solution and the molar ratio for HSO3- to the total solution concentrations all have significant impact on NO2 and NO absorption rates. While the solution concentration is constant, the absorption of NO mixture is strongly related to the ratio NO2/NOx. The absorption rate of NO is primarily affected by NO2 inlet concentration, and the NO absorption rate reaches the maximum value in (NH4)(2)SO3 solution with the increase of NO2 inlet concentration, which is determined by the reaction of NO and NO2 with SO32- as well as NO formation. Moreover, when the solution is NH4HSO3 the best ratio of NO2/NO for the maximum value of the NO absorption rate becomes less or smaller. Meanwhile, the presence of NO in the gas phase is also favorable to the absorption rate of NO2 in ammonium-sulfite or bisulfite solutions. The total results suggest that the coexistence of NO and NO2 in the flue gas could enhance the absorption of each other to some extent. (C) 2011 Elsevier B.V. All rights reserved.