This International Standard describes a method for the measurement of the mass of particulate matter in ambient air and is based on the absorption of beta rays by the particulate matter. This method applies to the determination of concentrations ranging from a few micrograms per cubic metre to a few milligrams per cubic metre contained in the atmospheres of urban, rural or industrial areas. The lower mass detection limit of the method is usually 15 ?g to 30 ?g of deposited mass per square centimetre of surface area, S, of the filter. This means, for a sampling time t of 3 h and a flowrate q of 1 m3/h, that the concentration detection limit ranges between 5 ?g/m3 and 10 ?g/m3, computed as follows: Concentration g / cm (cm (m / h) (h) 2 2 e j 3 S q t ) 1 Sampling techniques are not included in the scope of this International Standard. NOTE The concentration of particulate matter is calculated by dividing the mass deposited on a filter tape or individual filter, by the known volume of air sampled. However, concentration is dependent on the sampling technique used, for example, the design of the sampling inlet. Normally, for ambient-air particle sampling, large particles are filtered out by means of a sizeselective inlet (for example cascade impactor or cyclone filtration). The particle size limit is defined by the characteristics of the sampling head.