Getting the skinny on diesel emissions
Whether U.S. trucks and buses are meeting tougher federal emissions standards should become clearer under a pilot program slated to begin in July. Developed by the U.S. EPA, the California Air Resources Board (CARB), and diesel-engine manufacturers, the voluntary two-year program will analyze emissions from heavy-duty diesel vehicles operating under real-world conditions. The program will become mandatory starting with model year 2007, when EPA’s new tailpipe emission standards for NOx and particulate matter (PM) kick in.
Previously, the only way to test engine and vehicle emissions for certification purposes required pulling out the engine and running it through standard cycles on a laboratory dynamometer, explains Joe Suchecki, with the Engine Manufacturers Association. But the cycles don’t cover all conditions, like driving uphill, stop-and-go traffic over long periods, heavy loads, or different altitudes. Research has shown that operating conditions can strongly affect diesel vehicles’ emission levels (Environ. Sci. Technol. 2004, 38, 152A). Consequently, engine manufacturers had no way of fully ensuring compliance with EPA and CARB standards, which were imposed in 2000 and require emissions to be within a certain range of the limit at all times, regardless of operating conditions and vehicle age, Suchecki notes.
Under the new program, however, portable emission measurement systems (PEMS), which are about the size of a briefcase, will be attached to selected engines to continuously record exhaust emissions of hydrocarbons, carbon monoxide, NOx, and PM as the vehicle is driven. The process is more accurate and less expensive than the dynamometer, according to Karl Simon, acting assistant director of EPA’s Office of Transportation and Air Quality. Moreover, “The mobile monitoring system will allow us to test a lot more trucks,” says Michael Carter, chief of CARB’s emissions research and regulatory development branch.
“For the first time, we’ll be able to actually look at the in-use, heavy-duty fleet, and this will allow us to see if they comply with the emissions standards that they’re originally certified under,” Carter notes.
The accuracy margins of the relatively new PEMS technology will be determined during the pilot program; up to 25% of engine families will be selected for testing in a given model year, according to EPA. If noncomplying engines are identified, the manufacturer will have to test more engines to determine whether engine redesigns are necessary. EPA and CARB officials plan to use the data to make independent compliance evaluations and to help devise emissions inventories. EPA estimates that the program will cost manufacturers $1.7 million annually. The program will be run by the companies, such as Caterpillar, Inc., Cummins, Inc., and Detroit Diesel Corp., that make the engines. “We’ll be relying on manufacturers to give us the data,” Carter points out. But “we do have the authority to do our own confirmatory testing to keep manufacturers honest.”
For more information on the in-use diesel engine testing program, go to www.epa.gov/otaq/hd-hwy.htm#inuse.
