 The substance measured may be either the contaminant itself or a biomarker which is specific to and indicative of an exposure to the contaminant.Biomarkers of exposure assessment is a measure of the contaminant or other proportionally related variable in the body.Air sampling measures the contaminant in the air as concentration units of ppmv (parts per million by volume), mg/m3 (milligrams per cubic meter) or other mass per unit volume of air.Samplers can be worn by workers or researchers to estimate concentrations found in the breathing zone (personal) or samples collected in general areas can be used to estimate human exposure by integrating time and activity patterns.