A ventilator assembly for removing contaminants in cooking exhaust includes a hood portion having a hood plenum, and a duct portion in fluid communication with the hood portion, where the duct portion has an inside cross-sectional area that is less than half of an average inside cross-sectional area of the hoodplenum. A fan is in fluid communication with the duct portion for drawing the cooking exhaust through the hood portion to the duct portion. At least one ultra-violet lamp is disposed in the duct portion, where the ultra-violet radiation from the lamp reacts with the cooking exhaust to generate ozone for oxidizing contaminants in the cooking exhaust.