Abstract: A process and an apparatus for forming aerosols of pesticidal chemicals, said process comprising vaporizing water in a steam generator fitted with a heater, heating the resultant steam to 110.degree.-800.degree. C in a superheating means, passing the superheated steam from the superheating means, while controlling its temperature, to an evaporator containing the pesticidal chemicals and connected to the steam generator through superheater thereby to effect the heating, evaporation and entrainment of the chemicals with steam, releasing the resulting entrained vapor in the air to form aerosols of the pesticidal chemicals. The aerosols are used to control indoor or outdoor fungi, bacteria, viruses, and insects.