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Breathing Easier: Chemistry Professor Studies Ways to Lower Air Pollution...continued
The small particles that are also characteristic of smog are directly responsible for the loss of visibility that often accompanies high smog levels. This aspect of smog has been a concern in the effort to protect the natural vistas characteristic of the nation's national park system. In addition, because these particles are about the size of the width of a human hair, they are able to deeply penetrate tissues in the lungs. It is not known how these particles might interfere with bodily functions, but there have been several studies that have correlated long-term exposure to high particle levels with increased mortality and increased incidence of cardiopulmonary diseases. The most telling of these reports showed that small particle smog pollution was responsible for a 30 percent higher overall death rate in Steubenville, a city in southeast Ohio that is host to a large coal-fired power plant, as compared to the similar, but relatively smog-free, city of Portage, Wisconsin.
My research is in the area of laboratory atmosphere chemistry, which is the field of atmospheric science that attempts to understand the fundamental chemical mechanisms that lead to the observed chemical composition of the atmosphere. In concert with measurements of the atmosphere made from ground-, aircraft-, or satellite-based instruments, and sophisticated computer models, this information can be used to understand current aspects of smog occurrences, reconstruct past events, and most importantly, predict future smog levels given certain emissions scenarios. My students and I have focused our efforts on understanding the chemical processes that lead to elevated levels of ozone. Although there are literally thousands of chemical reactions occurring simultaneously in the Earth's lower atmosphere, only the fastest of these processes contribute significantly to the formation of ozone. Therefore, the most fundamental data concerns the rate of these chemical processes, which is called the field of chemical kinetics.
Although there are laboratory techniques in which one attempts to simulate all of the relevant chemical reactions simultaneously, my research group seeks to study the rate of reaction of one of these chemical processes at a time, so as to be able to unambiguously interpret the results of the experiments. By performing many such measurements, a database of atmospherically relevant reactions can be built up, and the atmosphere can be accurately modeled. Based on years of effort by many researchers in this field, it is now well understood that high ozone levels are the result of elevated levels of hydrocarbons or nitrogen oxides, or both. Hydrocarbons are the chemical class to which most fuels belong: coal, natural gas, and oil. Nitrogen oxides are produced when air is heated to very high temperatures, which is common when hydrocarbons are burned to produce energy. Thus, elevated levels of these two species often coincide (particularly in urban environments). In my laboratory, we have investigated the ozone-producing efficiency of the hydrocarbons methane (better known as natural gas, the most common fuel for heating), ethane, and propane (used in gas grills). We are investigating the ozone-producing efficiency of isoprene, which is a naturally occurring hydrocarbon emitted by deciduous trees. In general, the different hydrocarbon species have dramatically different capacities to produce ozone, which is due to differences in their atmospheric concentrations and intrinsic chemical reactivity. Through the kind of work done in my laboratory, it is possible to identify chemical compounds whose emission into the atmosphere is particularly harmful.
Recently, the U.S. Supreme Court denied a challenge by several utility companies to overturn a 1997 decision by the U.S. EPA to significantly lower the levels of ozone allowed by the CAA. As these more stringent standards are put in place, an EPA study predicts that the incidence of respiratory disease will drop significantly in those areas that have not been considered in the past to be in violation of the CAA. However, these standards will be difficult to achieve, and policy makers must rely on an up-to-date understanding of the atmospheric chemistry of ozone production in order to make the most effective decisions regarding emission control strategies. As a result of the kind of laboratory experiments described above, and further advances in atmospheric monitoring and more sophisticated computer modeling, it is becoming more clear that long term elevated ozone levels are becoming a nationwide, if not global problem. At the same time, short-term acute ozone episodes of the kind seen in Los Angeles, Houston, and Atlanta, are increasingly understood to be the result of some curiously local aspects.
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