A process of producing sulfuric acid from feed gases containing 0.1-30% SO.sub.2. The process produces concentrated sulfuric acid from a feed gas containing 0.1 vol % to 30 vol % SO.sub.2, in particular a strong feed gas containing 6 vol % to 30 vol % SO.sub.2, that enables the gas entering the final wet condensing stage to have an acid dew point of below 260.degree. C., while at the same time achieving current requirements of acid mist emissions of about 20 ppmv without resorting to substantial air dilution of the strong feed gas.