Beyond the Tailpipe: Particulate Matter Pollution from Vehicular Emissions
Jesse Kroll, Assistant Professor, MIT Civil and Environmental Engineering, Chemical Engineering;
Description: It turns out that the exhaust exiting a car's tailpipe is just the first part of a complex journey of pollutants that scientists like Jesse Kroll are starting to map out. He wants to know just what these emissions consist of, how they change over time, and what their possible impacts are.
The term 'smog,' with which most cities have become all too familiar, is not really the direct result of vehicle emissions but the end"product of a photochemical process that was identified 60 years ago, according to Kroll. When nitrogen oxides and hydrocarbons from exhaust mix with sunlight, the result is smog, which itself comprises ozone and particulate matter. Neither of these is good for human or planetary health, and the bulk of these emissions come from vehicles.
Scientists have done a good job dissecting ozone and its impact both at ground level and on the atmosphere, hence worldwide regulations attempting to reduce these emissions. But researchers understand a lot less about particulates, micron"sized chemicals born aloft in aerosol form. They matter because, as Kroll relates, epidemiological studies link high levels of particulates to increased rates of mortality (lung cancer, cardiopulmonary disease), and to impacts on climate. By scattering or absorbing light, particulates can mask the effects of global warming. Additionally, "we just don't like to see this pollution," says Kroll.
The traditional picture of the composition of these particles has proven inadequate, says Kroll, because it hasn't taken into account the way particulates interact over time with each other and under different conditions once they exit vehicles -- forming wholly new compounds. Regulators have typically focused on what pours out of tailpipes in the first few seconds of burning fuel.
Kroll, intrigued by how secondary aerosols form, and where they end up, has developed a new instrument to measure and identify the organic carbon particulates when burned at different temperatures. He has also run experiments over days in a refrigerator"sized "smog chamber" outfitted with UV lights to see what reactions occur. At different points in this box, the particles shift into gas phase, and back, as oxidation occurs. Ultimately, Kroll wants to measure the lifecycle, quantities and properties of this plume of pollutants, as they transform from primary to secondary aerosols, with the hope of offering regulators a more fine"grained picture of potentially harmful emissions.
About the Speaker(s): Jesse Kroll received A.B., A.M. and Ph.D. degrees from Harvard University. His research involves the experimental study of the properties and chemical transformations of organic species in the Earth's atmosphere. Atmospheric organics play several roles of central importance to environmental science: they affect air quality by forming secondary pollutants such as ozone; they make up a large fraction of particulate matter, with serious implications for human health and climate; and they exchange with other domains in the environment (oceans, soils, etc.), influencing biogeochemical cycles and the distribution of pollutants. A detailed understanding of these effects requires an improved characterization of the sources and evolution of atmospheric organics.
Host(s): School of Engineering, Transportation@MIT
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