The article gives results of an investigation of the effect of relative humidity (RH), time, and aeration during calcium hydroxide--Ca(OH)2--storage for its effect on sorbent handling and reactivity with sulfur dioxide (SO2). Investigated was the effect of sorbent storage conditions of time (1-24 hr), RH (zero-90%), silo wall material, and aeration on handling properties of flowability and floodability and their subsequent effect on sorbent/SO2 reactivity. Increased RH in the storage chamber and prolonged storage increased floodability, as predicted by the angle of difference. No significant effect of RH on the flowability of Ca(OH)2, as predicted by the angle of repose, was detected. The importance of silo wall material on proper sorbent discharge pattern has been demonstrated through testing on four common surfaces. The effect of sorbent storage conditions on the reactivity of Ca(OH)2 with SO2 was evaluated in a short time differential reactor (STDR)operated under conditions typical ofdry sorbent injection for SO2 control near the preheater. Increased RH and aeration with air during storage resulted in decreased reactivity of Ca(OH)2 with SO2. The effect of storage conditions on handling of novel Ca(OH)2-based sorbents for the removal of SO2 was also evaluated. ADVACATE sorbent appears to have significantly better handling properties than the other sorbents tested.