Sampling conventions for estimating ultrafine and fine aerosol particle deposition in the human respiratory tract.

OBJECTIVES: To provide targets for personal samplers designed for estimating particle deposition at distinct locations in the body, accounting if necessary for inter- and intra-person variation. PROPOSAL: Ultrafine and fine aerosol sampling conventions are proposed for approximating the deposition efficiency for five distinct loci of the respiratory tract. The 2 × 5 = 10 conventions represent averages over variation in physical activity level, posture, sex, and breathing mode. Recognizing three approximate relationships among the 10 deposition efficiencies, the number of independent conventions is reduced to only seven, namely three ultrafine and four fine aerosol conventions. The ultrafine and fine conventions are defined as ideal sampling efficiencies in terms of thermodynamic (independent of particle density) and aerodynamic diameter, respectively. APPLICATION: Addition of measured mass, surface area, or particle count from aerosol collected by sampler pairs in agreement with convention can be used to estimate dose (prior to clearance) at a particular locus in the mean over breathing conditions ranging from sitting, to light, or to heavy exercise, normal or mouth breathing, and male or female, with aerosol density effects partially corrected automatically by the separate aerodynamic and thermodynamic sampling. Linear combinations of the conventions can be used for yet simpler sampling, though with limited distinctness as to deposition locus. Alternatively to estimating simply a mean, the large inter- and intra-person variation (relative standard deviation of the order of 100%) corresponding to the wide range of breathing conditions can be approximately corrected by using 'arrays' of samplers in agreement with convention, given suitable profiling of the individual whose dose is to be assessed. OUTCOME: The intent behind the proposed conventions is not to eliminate the current aerosol penetration conventions, which have found international application in exposure assessment particularly for determining compliance with standards on acceptable aerosol levels. The aim is to promote personal sampler design leading to more sharply defined health research than can be done at present.