Formaldehyde is a major indoor pollutant over the world and its high release over the national standards in developing countries, such as China, harms people's health seriously. In this work, an investigation is carried out in a stirred vessel with a plain gas-liquid interface for the absorption of lean formaldehyde from pollution air by Na2SO3 solution at 25 degrees C. Experiments are conducted with Na2SO3 concentrations of 0.01-0.30 kmol m(-3). The results show that the Na2SO3 solution is an effective absorbent to remove lean formaldehyde from polluted air. The experiments reveal that the absorption rate is considerably influenced by the gas flow rate and formaldehyde concentration. The Na2SO3 concentration has little effect on the absorption rate, and the loading content of formaldehyde reduces the absorption rate only if the formaldehyde concentration approaches or exceeds the concentration of Na2SO3 solution. A theoretical model is developed and used to successfully calculate the absorption rate with the overall relative deviation of less than 15% to the experimental data. A possible process of the absorption method is also proposed in this paper. The analysis shows that the proposed process is feasible in removing formaldehyde from indoor air. (c) 2005 Elsevier B.V. All rights reserved.