ISO 13138:2012 specifies sampling conventions to define idealized samplers for estimating the deposition of non-volatile, non-hygroscopic, non-fibrous aerosols in five specific loci of the respiratory tract. The five loci consist of the anterior and posterior areas of the nasal passages, the ciliated and non-ciliated parts of the tracheobronchial area, and the alveolar (gas exchange) region.

The conventions are separated into three independent sampling efficiencies defined in terms of thermodynamic diameter characterizing the diffusive (Brownian) motion of sub-micrometre particles and four efficiencies in terms of aerodynamic diameter 0,1 μm characterizing deposition by impaction, interception or gravitational settling. Each conventional curve has been developed as an average of 12 deposition curves corresponding to 12 breathing conditions ranging from sitting to heavy exercise, male vs female, and breathing mode (mouth vs nasal breathing).