On Cu(110)-p(2x1)-O at 300 K SO2(g) reacts stoichiometrically with O(a) to form a surface covered with both c(4x2)-SO3 and p(2x2)-SO3 structures. With heating SO2(g) evolves from the surface in distinct reaction-limited states at 384 K, 425 K, and 470 K, and the surface reverts to its initially oxidized state. On Cu(110), SO2(g) adsorbs molecularly below 300 K; upon annealing to 300 K, the sulfur dioxide disproportionates according to 3SO(2)(a)-->S(a)+2SO(3)(a) with concomitant desorption of excess SO2(a). The surface formed in this manner exhibits large c(2x2)-S domains which encompass scattered c(4x2)-SO3 and p(2x2)-SO3 structures in a 1:2 coverage ratio. After being annealed to 400 K, the surface exhibits large p(2x2)-SO3 domains surrounding smaller c(4x2)-SO3 and c(2x2)-S islands. Continued heating past 400 K results in decomposition of sulfite according to SO3(a)-->SO2(g)+O(a), evolving sulfur dioxide at 470 K and leaving the surface covered with atomic sulfur and oxygen. Real-time STM images show the mobility of oxygen at island boundaries and the mobility of sulfite amid the p(2x1)-O structures. STM measurements suggest that the sulfite occupy four-fold hollow sites.