The solubility behavior of SO2 in 1-butyl-3-methylimidazolium acetate ([BMIm][OAc]) was investigated. The solubility of SO2 in [BMIm][OAc] was measured to be 0.6 in mole fraction at 50 degrees C in a stream of SO2 gas. The desorption of SO2 from [BMIm][OAc] was never completed, until the temperature was raised to 170 degrees C in a stream of N-2, indicating that the absorption of SO2 is irreversible at the experimental condition. An in-situ IR study showed that acetate anion in [BMIm][OAc] transformed into acetic acid during the SO2 absorption. After removing acetic acid at 170 degrees C by evacuation, the bands at 1210, 1045 and 850 cm(-1) appeared in IR spectra. The bands at 1210 and 1047 cm(-1) were assigned to S-O stretching mode of HOSO2- (an isomer of HSO3-) and the band at 885 cm(-1) was assigned to the symmetric stretching mode of HO-S. FT-IR study suggested that acetic acid and most plausibly [BMIm][HOSO2] were generated from the interactions of [BMIm][OAc] with SO2 and adventitious water in feed gas and/or [BMIm][OAc] during absorption-desorption process. [BMIm][HOSO2] recovered after removing acetic acid was found to be a new and reversible SO2 absorbent with the SO2 absorption capacity of 0.55 in mole fraction. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.