Abstract: A personal dosimeter for measuring the average concentration of undesirable contaminants gases such as nitrogen oxide includes a gas permeable web-like wafer formed of a material inert to polyamine. The wafer has a surface area having a numerical value at least one thousand times the value of the axial width of the wafer. The wafer is soaked in an absorptive medium not containing the ambient contaminant gas to be measured. The wafer, so soaked, is inserted within a gaseous impermeable housing from which the wafer may be selectively release and re-inserted. During an interval of release of the wafer, it is exposed for a predetermined interval of time to the ambient atmosphere. After re-insertion, the dosimeter is taken to an analysis site at which the wafer is removed and the molar concentration of products reaction with the atmospheric contaminant is measured.