Abstract: A method of removing NO.sub.x and SO.sub.2 from an exhaust gas containing NO.sub.x and SO.sub.2 which comprises contacting an exhaust gas containing NO.sub.x and SO.sub.2 with an aqueous solution containing M.sub.2 SO.sub.3, an iron ion and an aminopolycarboxylic acid to absorb NO.sub.x and SO.sub.2 in the aqueous solution and treating the resulting absorbing solution while preventing a contact of the solution with the exhaust gas, thereby to form M.sub.2 S.sub.2 O.sub.6 in the absorbing solution and reducing NO.sub.x to N.sub.2. The M.sub.2 S.sub.2 O.sub.6 formed in the absorbing solution can be easily removed by crystallization separation. With such method, NO.sub.x and SO.sub.2 can be removed from exhaust gases at high rates and the absorbing solution can be easily regenerated and recycled to the absorbing zone.

Abstract: A method for removing nitrogen monoxide effectively from a nitrogen monoxide-containing gas which comprises contacting a nitrogen monoxide-containing gas with an aqueous solution containing a ferrous ion complex formed from a ferrous ion and an organic compound of 2 to 24 carbon atoms having in the molecule at least one atomic group selected from mercapto, amino, imino and nitrilo groups. When a sulfite or sulfide is present in the above aqueous solution, the nitrogen monoxide-absorbing capacity of the aqueous solution can be enhanced and nitrogen monoxide absorbed in the aqueous solution is reduced to non-toxic nitrogen. According to this method, nitrogen monoxide can be removed effectively, even if the gas to be treated contains an oxidizing substance such as oxygen.