Aerosols comprising droplets dispersed in a carrier gas, wherein at least some of the droplets contain an antagonist effective to inactivate a biocide are provided. The droplets may contain the biocide and the antagonist that reacts with the biocide to render it harmless. The biocide is used for disinfection or sterilization, and the nature and concentration of the antagonist is selected, or means are provided, to ensure that the time required for the antagonist to render the biocide ineffective is longer than the time required for the biocide to be effective for a desired level of disinfection or sterilization. Methods of manufacture of aerosols are also provided.