Inter- and intra-subject variability of kinetics of airway exhalation and deposition of particulate matter in indoor polluted environments.

PM 2.5 generated by indoor combustion activities can contribute significantly to personal PM exposure. The aims of this study were: (1) to validate a device specifically designed to study the kinetics of particle exhalation and the percentage of airway particle deposition (%DEP) in polluted indoor environments (welding fumes, environmental tobacco smoke - ETS) and (2) to assess the intra- and inter-subject variability of the signal.The device was tested on 14 subjects exposed to welding fumes and 10 subjects exposed to environmental tobacco smoke (ETS), performing repeated measures at different environmental PM concentrations.The intra-subject variability of the signal for particles with diameter 0.3-1.0. μm showed a geometric mean of %CV always below 6%, despite the values of %DEP.In the welding fume study, the increase in airborne 0.5-1.0. μm PM concentrations between the consulting room and production department was explainable in terms of increased density due to the metallic composition of particles.The %DEP of 0.3-1.0. μm ETS particles decreased with airborne PM concentration due to the technical limits of a laser particle counter and the perturbation induced by the physical characteristics of ETS PM. However, also at those extreme conditions, the signal remained repeatable and the individual susceptibility to PM remained substantially unaltered.In conclusion, the versatility and portability of our device, together with the repeatability of the signal, confirmed that the kinetics of exhaled particles and %DEP could be routinely measured in polluted environments and used to define individual susceptibility to airborne particles.