A new research program at the Commerce Department's National Institute of Standards and Technology will help U.S. auto manufacturers develop technology needed to develop and test low- emission vehicles. The program, done in cooperation with regulatory agencies, also eventually could help emission testers measure a variety of exhaust gases in a few seconds.
Auto makers need new measurement technologies and standards in order to design cars and trucks that will meet increasingly stringent federal Clean Air Act requirements and California emission standards. NIST's Chemical Science and Technology Laboratory is collaborating with the American Industry/Government Emissions Research Consortium to establish a new program directed toward the development of new technologies and standards for the real-time measurement of several targeted chemical species in automotive exhaust. AIGER is an umbrella group that includes the Environmental Research Consortium (ERC members are Chrysler, Ford, General Motors and Navistar), the California Air Resources Board and the EPA.
The new research effort includes an "electronic nose," a new primary flow meter calibration facility, automobile exhaust analysis using infrared light and microwaves, and gas cylinder standards. Each project incorporates sophisticated techniques to assist in accurately measuring very low levels of exhaust gases.
NIST chemists have dubbed one project—an array of micro- sensors, detectors and a microprocessor on a credit-card-size device—the "electronic nose." Auto manufacturers and emissions testers around the country may one day rely on this electronic nose for detecting more than a dozen oxygenated hydrocarbons in auto exhaust in order to comply with Clean Air Act requirements.
NIST is working to improve the selectivity and sensitivity of microsensors made on a silicon chip. Microsensors, manufactured using integrated circuit technology, contain a heater, thermometer and a pollutant-sensing metal oxide film. Arrays of microsensors are needed to sense multiple pollutants. Temperature changes in each microsensor produce sensing response changes that allow detection of pollutants and measurement of their concentrations. Researchers at the University of Maryland and the National Security Agency's Microelectronics Research Laboratory are helping NIST develop the microsensor arrays.
Another project that may help auto manufacturers accurately measure ultra-low levels of pollutants in automotive exhaust is the development of two new spectrometers. One is an extremely sensitive, automated microwave spectrometer that can detect pollutants in the parts-per-billion range. The spectrometer can distinguish reliably between closely related molecules in exhaust. Another advantage is that it measures gases very quickly—several times a second—as they are emitted from a source.
The instrument uses microwaves to excite gas molecules and measures the energy they emit during relaxation. The primary disadvantage is low sensitivity for formaldehyde and methanol. Researchers in the NIST Physics Laboratory are building a portable version of the instrument for field tests at a vehicle emissions testing facility.
The other spectrometer being designed will use infrared light to measure oxygenated hydrocarbons, including formaldehyde and methanol. Currently, there are no analytical techniques that provide real-time analyses for all the hydrocarbon gases specified in the Clean Air Act. Combining microwave and infrared spectroscopy may provide the necessary capabilities.
The spectrometer would use two infrared lasers. One beam will pump or excite the gas molecules, and another will probe them to measure how much energy was absorbed. Each molecule has a specific signal, which the spectrometer will be able to identify.
A third project is providing AIGER members with Standard Reference Materials for evaluating the accuracy of new analytical methods being developed for measurement of auto exhaust from the "low emission vehicles" of the future. The first such SRM, a gas cylinder with 0.25 micromoles per mole (parts per million) of propane in air, will be available later this year. A procedure for the on-demand production of formaldehyde in air is scheduled for completion this fall.
AIGER members will use these new SRMs as a measuring stick to assess the accuracy of various techniques and instruments used for measuring pollutants in auto exhaust. The EPA and the California Air Resources Board both require that calibration gases for emission monitoring be traceable to NIST gas standards. NIST chemists are developing new standards of various gases in differing concentrations as necessary for American automobile manufacturers and regulatory agencies to meet new vehicle emission regulations.
A final NIST/AIGER project addresses the need for accurate measurements of exhaust flow rates. At present, vehicle manufacturers rely on dilution techniques in the measurement of exhaust emissions produced by a vehicle during testing. Future regulations will require very low levels of exhaust emissions and render current dilution methods unsuitable (given that exhaust emission levels will soon approach those in ambient air). To address the resulting detection problems, sampling systems are being developed that withdraw small amounts of raw exhaust from the vehicle and then dilute with known amounts of pure nitrogen or "zero" air prior to measuring the concentration. To operate the extraction/dilution system and to relate the concentration to total emission levels requires direct measurement of total exhaust volume flowrate.
To help AIGER members ensure accuracy in measuring exhaust flow rates, NIST is setting up an exhaust meter calibration facility. Auto manufacturers will be able to verify the accuracy of their exhaust flow meters at the new NIST facility, which is expected to open in 1996.
As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.