A system for removing SO.sub.2, NO.sub.2, and other contaminants from flue gases uses hydrogen peroxide (H.sub.2 O.sub.2) as the reagent to convert the oxides of sulfur and some of the oxides of nitrogen (NO, NO.sub.2, etc.) to more stable oxidation states. Acids formed as a result of this conversion, namely sulfuric acid (H.sub.2 SO.sub.4) and nitric acid (HNO.sub.3) can then be neutralized with limestone or, alternatively, the sulfuric and nitric acids can be collected and processed for sale as an industrial product.