Ozonators were mainly used in mid-sized to large boiling houses and heat factories. Furnace ozonators could potentially remove some pollutants from exhaust, including volatile organic compounds (50% reduction), carbon monoxide (80% reduction), and nitric oxides (90% reduction for NO and 80% reduction for NO2 when using a steam moisturizer). However, furnace ozonators would not remove other pollutants like carbon dioxide, hydrocarbons, or sulphur oxides (except a potential 20% reduction of SO2 with steam).