This paper looks at the development of a two-stage chemical scrubber for NOx control. In the first stage, the most practical oxidizing agents for NO oxidation are sodium chlorite and sodium hypochlorite. Although a considerable amount of work has been done on the reaction kinetics of NO2 with Na2SO3, there are major gaps in developing an Na2SO3 aqueous solution for NO2 absorption in the second stage. Of particular importance is the rate of chemical absorption. A pilot-scale research program was initiated to evaluate the absorption rate of NO2 with Na2SO3 aqueous solution in a packed tower. The research is directed at obtaining height of a transfer unit (HTU) for NO2 absorption, and to determine reasonable operation conditions for the packed bed scrubber. A sulfite concentration of 0.25 M is essential to have a reasonable HTU in 2 to 5 feet for a gas rate between 1,050 to 2,350 lb/ft2 hr. The results indicate that the scrubbing effectiveness of NO2 increased with the L/G ratio, and an L/G of more than 3 is required for high NO2 absorption.