A method of measuring density of a sterilant aerosol e.g. aqueous hydrogenperoxide, in a gas stream (such as astream of air) for the purposes of measuring sterilant dosage comprising:passing a gas stream at flow rate past an electrically heatedelement and measuring a first cooling effect, passing an aerosol suspended ina gas stream at flow rate past an electrically heatedelement and measuring a second cooling effect and measuring the differencebetween the first cooling effect and second coolingeffect and correlating the difference with aerosol density. The total dosagecan thus be determined. A measured dosage of asterilant aerosol can be delivered by way of a feedback loop to halt furtherdelivery of sterilant aerosol when the amount of aerosoldelivered reaches a predetermined dosage. The methods allow sterilization tobe certified.
