Analysis of Respiratory Deposition Dose of Inhaled Ambient Aerosols. K. Chong, US Environmental Protection Agency, NC; S. Hu, IIT Research Institute; and P. Jaques, University of California, Los Angeles
Although many epidemiological studies have shown a consistent correlation between observed health effects and mass concentration of airborne particulate matter (PM), some evidence suggest that particle number or surface area may also play an important role in PM associated health effects. However, specific quantitative data are lacking for respiratory dose of heterogeneous ambient aerosols and the relationship between different size fractions vs. their relative contributions to the number(N), surface area (SA) and mass (M) deposition. We analyzed respiratory deposition of a typical bi-modal ambient aerosol (MMD1 = 0.3 micron, MMD2 =5 micron and GSD = 2.0 for each mode) for different size fractions (eg,0.04, 0.06, 0.1, 1, 3 and 5 micron), and deposition dose was analyzed for M, N and SA of particles in different lung regions. At a tidal volume of500 ml and breathing frequency of 15 breaths/min the results show that 3and 5 micron fractions are a dominant contributor for mass deposition. Number deposition was dominated by ultrafine size fractions. However, surface area deposition peaked at the size fraction of ~0.1 micron, and both 0.04 and 5 micron fractions were notable contributors. The finding was consistent for the tracheobronchial (TB) and alveolar (AL) region as well as the whole lung. However, deposition dose was several time greater in TB than AL regardless of particle size and dose metrics. In summary, for atypical bi-modal ambient aerosol lung deposition dose is dominated by coarse particles for mass and by ultrafine particles for number, but all sizes are important for surface area. The results suggest that from the physical dose metric point of view the particle size itself may have an ambiguous role on causal mechanisms of PM-associated health effects. Chemical compositions and other particle properties may be examined along with particle size to obtain realistic dose-response relationship.
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