Novel methodology for estimation of mass and surface area of aggregated particles deposited in the human respiratory tract

The particle mass and surface area is believed to be crucial parameters for the health effects of inhaling nonsoluble air-borne particles. Often the deposited dose and particulate surface area are estimated from particle number concentrations measured by DMA techniques. For spherical particles such estimations are good. For non-spherical particles, however, the estimations can deviate from the real deposited surface area or mass by an order of magnitude. Aggregated or agglomerated particles require additional information about both particle shape and particle effective densities. The aim of this work is to describe and apply a methodology for assessing surface area and mass of aggregated/agglomerated particles based on number size distributions measured by DMA-techniques. The method is applied in three studies: estimating the deposition in the human respiratory tract of diesel soot, deposition of gold aggregates in protein solutions and direct unto cell cultures (Savi et al., 2008). The principle of the method used to estimate the surface area size distribution is shown in Figure 1. As input (i) the mass of the individual aggregates of a certain mobility diameter magg(dme), (ii) the primary particle size (dp), and (iii) number size distribution (dNagg/dlogdme) are needed. For mass determination of individual aggregates the novel DMA-Aerosol Particle Mass Analyzer (DMAAPM McMurry et al., 2002) is used. The mass size distribution of the aerosol is estimated by combining the results of the DMA-APM system and the number size distribution. For estimation of surface area the size of the primary particles is also needed, here estimated from TEM images. From magg(dme) and dp the number of primary particles of the individual aggregates of a certain size (Np(dme)) is calculated (assuming a density of the primary particles of ρp=1.8 g/cm for soot and 19.3 for gold) according to . By combining Np(dme) and the particle number size distribution, the distribution of the total number of primary particles of all aggregates of a certain dme is

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