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Inhalation Exposure and Lung Dose Analysis of Multi-mode Complex Ambient Aerosols
Citation:
Kim, C. AND S. Hu. Inhalation Exposure and Lung Dose Analysis of Multi-mode Complex Ambient Aerosols. Presented at Annual Conference of American Association for Aerosol Research, October 08 - 12, 2012.
Impact/Purpose:
During exercise breathing patterns change by increasing ventilation rate and this has a direct impact on risk to exposure to ambient pollutants.
Description:
Rationale: Ambient aerosols are complex mixture of particles with different size, shape and chemical composition. Although they are known to cause health hazard, it is not fully understood about causal mechanisms and specific attributes of particles causing the effects. Internal dose is a key factor for determining the health risk of inhaled particles, but unlike a single pollutant an accurate estimate of dose for a complex mixture is a formidable task. Dose of each specific component of the mixture and their relevant dose metrics may help improve understanding of health effects associated with ambient particulate matter (PM). Method: We have attempted to analyze lung deposition dose of typical bimodal ambient aerosols composed of two different size distributions representing fine and coarse mode aerosols; mass median diameter of 0.3 um and 5.0 um with geometric standard deviation of 1.8 – 2.0. Mass ratios (MR) between the two distributions were varied with an increment of 0.1, thus covering a wide range of distribution patterns. Lung deposition was assessed, by using a mathematical model built upon Weibel’s lung morphology, for mass, surface area and number of particles for the entire size distribution and also each of three size fractions, ultrafine (PM0.1), fine (PM0.1-2.5) and coarse (PM2.5-10) fractions at inhalation patterns mimicking resting and mild to moderate exercise. Chemical dose was also assessed using chemical speciation data vs. particle size fractions of typical urban area aerosols compiled by EPA. Results: Broadly distributed bimodal aerosols affect lung deposition variably in different size fractions. Overall, as the mass ratios shift from coarse to fine mode, total and coarse PM mass dose decreases, but fine PM dose increases particularly in the deep lung region. Surface area deposition is resulted mainly from fine fraction particles except for a very skewed distribution (MR<0.2) whereas number deposition comes entirely from both fine and ultrafine fractions as long as MR> ~0.03. During exercise, lung deposition showed a slight decrease in fine fractions but no practical changes in coarse fractions compared with resting condition. Conclusions: Different size fractions in the bimodal distribution aerosols contribute differently to lung deposition dose in terms of mass, surface area, number and chemical species. Significance of roles of each size fraction and their combined effects need to be considered in health risk assessment. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.