At conditions typical of a bag filter in a coal-fired Rue gas, nitrogen dioxide (NO2) diluted with nitrogen was exposed to various alkaline and nonalkaline solids in a packed-bed reactor. On nonalkaline solids, 3 mol of NO2 reacted readily with water to produce 2 mol of nitric acid (HNO3) and 1 mol of NO. Alkaline solids such as calcium hydroxide or calcium silicate (from lime and fly ash) produced less NO and neutralized the nitric acid on the surface. A mathematical model developed to predict rates of NO2 removal on these surfaces successfully compared experimental and predicted rates. These results are relevant to technology for removal of NOx by addition of methanol to dry scrubbing systems for flue gas desulfurization.