Size, source and chemical composition as determinants of toxicity attributable to ambient particulate matter

Chemical characterization of particulate emissions from diesel engines: A review

New materials capable of separating mixtures of saturated, unsaturated, and aromatic hydrocarbons can enable more efficient industrial processes and cleaner energy. Outstanding challenges in hydrocarbon separations stem from the similar structures, properties, and reactivities of the molecules comprising many of these mixtures. With high surface areas, tunable pore geometries, and adjustable surface functionality, metal–organic frameworks hold tremendous promise for effecting previously difficult or impossible separations. In this review, we provide a comprehensive account of the metal–organic frameworks that have been investigated for hydrocarbon separations within the context of their potential relevance for separating various industrial alkane-, alkene-, and aromatic-containing mixtures.

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Hydrocarbon Separations in Metal–Organic Frameworks

Source specificity and atmospheric processing of airborne PAHs: Implications for source apportionment

Carbonaceous aerosol, a major component of particulate matter (PM), gases, and vapors in the atmosphere, has been associated with natural and anthropogenic air pollution, reduced visibility, climate modulation, material and ecosystem damage, and adverse health effects. More recently, epidemiological studies have indicated associations between organic fractions of ambient PM and adverse respiratory and cardiovascular health outcomes. The effects of the non-PM components of the organic aerosol have received less attention because their measurement in the general environment is not mandated. This article summarizes current knowledge of the nature, prevalence, and health effects of organic aerosols encountered in the outdoor environment, identifies key information gaps, and presents a conceptual framework for research priorities for resolving those gaps. The broad, diverse class of air contaminants comprising organic aerosols may be more important to public health than the modest attention given to them. This review focuses on hazard identification and exposure assessment for evaluating risks to public health from ambient organic aerosols. Current knowledge is insufficient to support a quantitative characterization of the aggregate risk from organic air contaminants. Assessments should be done for individual species or mixtures. Efforts should be taken to assemble and evaluate a common set of standard reference materials for both organic speciation and health response assays. A greater standardization of approaches across studies and laboratories would be useful to achieve uniformity in assessing health effects. Multidisciplinary research efforts are needed to improve the current regulatory-driven air quality monitoring networks for epidemiological studies. The limited array of biomarkers linking organic aerosols to health effects needs to be expanded and specific organic compounds or classes that are associated with biological effects in human cells or animal studies need to be tested for better understanding of the exposure-response relationship.

Health Effects of Organic Aerosols

Emission measurements were obtained for a variety of military vehicles at Hill Air Force Base (Ogden, UT) in November 2000 as part of a Strategic Environmental Research and Development Program. Aircraft ground support equipment vehicles using gasoline, diesel, and JP8 fuels were tested using chassis dynamometers under predetermined load. The exhaust from the tested vehicle was passed to a dilution tunnel where it was diluted 30-40 times and collected using Micro-Orifice Uniform Deposit Impactor (MOUDI) fitted with aluminum substrates, an XAD-coated annular denuder, and a filter followed by a solid adsorbent. All MOUDI substrates were analyzed for mass and for organic and elemental (EC) carbon by the thermal/optical reflectance method and for polycyclic aromatic hydrocarbons (PAHs) by GC/MS. Black carbon was measured with a photoacoustic instrument. The denuder and filter/solid adsorbent samples were analyzed for semivolatile PAH. Overall, there is more mass and higher EC contribution when the vehicle is run under higher load in comparison with the low load. However, older vehicles generally show more mass and EC emissions than newer vehicles, and there is a shift toward smaller particle sizes for the low load, which is most pronounced for newer vehicles. The particle-associated semivolatile PAHs and nonvolatile four-through six-ring PAHs are present predominantly on the submicron particles collected on MOUDI stages 0.1-0.18, 0.18-0.32, and 0.32-0.56 microm. For the low-load runs, the distribution of PAHs seems to be shifted toward smaller size particles. The gas-particle phase distribution of semivolatile PAHs depends also on the engine loading. For idle, not only are the more volatile two- and three-ring PAHs, from naphthalene to dimethylphenanthrenes, retained on the denuder portion, but also less volatile four-ring PAHs, such as fluoranthene and pyrene, are retained by the denuder at the 80-90% range, which implies that they are present predominantly in the gas phase. In contrast, for engines under high loads, a much larger portion of three- and four-ring PAHs are partitioned to the particle phase.

D. A. Wagner

Papers

Phase and size distribution of polycyclic aromatic hydrocarbons in diesel and gasoline vehicle emissions.