Published by the MIT News Office at the Massachusetts Institute of Technology, Cambridge, Mass.
Published by the MIT News Office at the Massachusetts Institute of
Technology, Cambridge, Mass.
NEW CARS NEEDED Team Seeks New Emissions Marker By Elizabeth A. Thomson News Office A car, a tent and a large flexible tube connecting the two by the muffler make up the visible parts of the apparatus Ilhan Olmez and Xudong Huang are using to collect motor vehicle emissions in a study to help scientists track car emissions in urban air around the world. For years researchers determined the contribution of motor vehicle emissions to the urban atmosphere by analyzing the amount of lead in the air from leaded gasoline. But with the switch to unleaded gas, scientists lost their marker. "Right now we are not able to accurately calculate how much motor vehicles are contributing to our air," said Dr. Olmez, a senior radiochemist at the Nuclear Reactor Lab. And that data is important to health professionals and regulatory agencies, especially in cities like Los Angeles where car emissions are major contributors to smog. So Dr. Olmez and Mr. Huang, a graduate student in nuclear engineering, are using MIT's research reactor to find a new marker. Specifically, the two are using a technique called neutron activation analysis to determine the composition of today's motor vehicle emissions, in particular the inorganic elements present and their concentrations. With those data they can find a marker. A good marker, said Dr. Olmez, will be an element or combination of elements emitted in relatively high concentrations that stays around in the air for a while. He believes that the eventual marker will actually come from a car's catalytic converter rather than gasoline. "Unleaded gasoline emits organics that are not useful for tracer purposes because they change their chemical compositions immediately after they are emitted," he said. Today's catalytic converters, however, emit elements that are stable and can be traced. Preliminary results with samples provided by General Motors showed that cerium, lanthanum and some other elements might make good markers, Dr. Olmez said. To get more conclusive results, over the next few weeks the researchers hope to sample emissions from more than 50 new cars. "The more cars I sample, the more reliable the data," Dr. Olmez said. That's because emissions from different brands of catalytic converters vary. "Japanese converters in general emit more lanthanum, American converters more cerium," Dr. Olmez said. He plans to average the data to arrive at a reliable composition for motor vehicle emissions. (If you have a 1991 car and would like to participate in the study, call Dr. Olmez at x3-2995. Sampling takes about 15 minutes.) In the final phase of the study, Dr. Olmez, in collaboration with the University of Maryland, will sample air from the Baltimore Harbor Tunnel to compare the chemical composition of the air there today with the composition measured several years ago. When the study is completed, the latest elemental composition for motor vehicle emissions will be included in the EPA's source composition library, which contains the chemical compositions and markers for everything from power-plant emissions to wind-blown dust. Then, said Dr. Olmez, "scientists in, say, Michigan can use this information to calculate the contributions of motor vehicle emissions to their atmosphere."