Crushed powder mixtures of calcium sulphite and calcium nitrate exhibit an exothermic reaction between 650 and 700 K. This rate process has been investigated by dynamic and isothermal DSC experiments, complemented with isothermal rate studies based on gas evolution in a vacuum apparatus, together with some product analyses. It is concluded that the overall reaction is complicated, including several concurrent contributing chemical changes, in which sulphite oxidation to sulphate is a dominant process, accompanied by some nitrate decomposition. On heating to higher temperatures (above 800 K) a second endothermic reaction was identified as the melting and breakdown of calcium nitrate. These processes occurred at temperatures somewhat less than those characteristic of the pure salt, possibly due to the presence of products from the first reaction including small amounts of Ca(NO2)(2). The dominant exothermic reaction was accompanied by fusion, at temperatures significantly below the melting point of either reactant. This may be due to the intermediate formation of Ca(NO2)(2), melting point 551 K, or the generation of liquid product following hydrolysis reactions with water evolved during dehydration of reactant CaSQ(3). 1/2H(2)O, with which the exothermic oxidation overlapped. This dehydration step was a precursor to sulphite oxidation. A detailed reaction mechanism is not proposed here due to the difficulties of separating the contributions from the several probable concurrent participating reactions. The role of the fluid reactant believed to be active in the oxidation process, and containing NO3-, NO2-, SO32- and possibly SO42-, in desulphurization processes, is discussed as a possible route towards removing the precursors to acid rain from coal combustion emissions. It is known that CaCO3 reacts with NOx to form Ca(NO3)(2), The present work identifies the liquid medium recognized in the exothermic reaction as enabling the oxidation of CaSO3 --> CaSO4 to proceed to completion at a.lower temperature than the slow and product-opposed reaction of CaSO3 with oxygen gas. Aspects of the chemistry of this complicated reaction and its potential value in pollution abatement are discussed.