Development of an Empirical Formula for Describing Human Inhalability of Airborne Particles at Low Wind Speeds and Calm Air.

Based on experiments conducted in low wind speed and calm air environments, the current International Organization for Standardization (ISO) and European Committee for Standardization (CEN) convention modeling human aerosol inhalability (i.e. aspiration efficiency) may not be valid when wind speeds are less than 0.5 ms-1. Additionally, the convention is based primarily on mouth breathing data and aerosols with aerodynamic diameters smaller than 100 µm. Since the convention's development, experimental inhalation data at wind speeds lower than 0.5 ms-1 for nose, mouth, and oronasal breathing have been generated for aerosols in a wider range of sizes (1.5-135 µm). These data were gathered and modeled with the intention of providing a simple convention recommendation for inhalability in low wind speed (>0 to <0.5 ms-1) and calm air (~0 ms-1) conditions to the ISO Technical Committee (TC) 146, Subcommittee 2, Working Group (WG) 1 ('Particle Size-Selective Sampling and Analysis'), as it relates to standard ISO 7708, and to CEN TC 137/WG 3, as it relates to standard EN 481. This paper presents several equations as possibilities, all relating aspiration efficiency to aerodynamic diameter. The equation AE=1+0.000019dae2-0.009788dae stands out as a possible new convention. This polynomial model balances simplicity and fit while addressing the weakness of the current convention.