Microtransport and partitioning of semivolatile organic compounds in combustion aerosols
Abstract
Recent epidemiological studies show that exposure to elevated levels of atmospheric particulate matter is associated with a significant increase in mortality and morbidity risk in humans. Although the causes of these responses are not well understood, many researchers believe that the toxicological effects of organic constituents sorbed to inhaled particulate matter may be partially responsible. Many of the most harmful organic constituents, such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and chlorinated dibenzodioxins and dibenzofurans, have moderate vapor pressures at ambient conditions. As such, these compounds partition between the gas phase and sorption to atmospheric particulate matter. Since the atmospheric fate of a compound is strongly dependent on the phase in which it exists, knowledge of gas-particle partitioning is critical to understanding the fate of these toxic compounds in the environment. Furthermore, since it has been shown that gas-particle partitioning equilibrium is oftentimes not achieved in real atmospheres, it is important to quantify the microtransport processes (e.g., diffusion) for these species in atmospheric particulate matter. In this work the microtransport and partitioning of semivolatile organic compounds in combustion aerosols is studied using a combination of smog chamber experiments and numerical modeling. Data and simulation results are presented for experiments in which polycyclic aromatic hydrocarbons are absorbed to and desorbed from particles over time scales ranging from hours to fractions of a second. These results show that dual-impedance radial diffusion models are able to closely reproduce these experimental results. An investigation of the sources of microtransport impedances is presented which suggests that the increased diffusion length due to obstructions in the diffusion pathway (i.e., tortuosity) is the primary mechanism impeding analyte microtransport in diesel soot particles. Example simulations are also included that show the importance of using radial diffusion models to simulate non-equilibrium partitioning in combustion aerosols. These simulations involve: (a)the partitioning of fluoranthene in a diesel soot aerosol while in transport from Cincinnati to Boston and (b)the deposition of benz(a)anthracene in the lung during the inhalation of a diesel soot aerosol.
- Publication:
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Ph.D. Thesis
- Pub Date:
- December 1999
- Bibcode:
- 1999PhDT.......102S
- Keywords:
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- Environmental Sciences, Engineering: Environmental, Health Sciences: Toxicology, Chemistry: Biochemistry, Chemistry: Organic, Physics: Atmospheric Science