An analysis of more than 40 transportation fuel studies has found strong evidence that substituting natural gas for diesel in heavy-duty trucks and buses reduces health risks from diesel exhaust.
This analysis was sponsored by Chicago IL-based GRI and conducted by Engine, Fuel, and Emissions Engineering Inc (EF&EE), Sacramento CA. Studies included research by the Environmental Protection Agency (EPA), National Renewable Energy Laboratory (NREL), Society of Automotive Engineers, California Air Resources Board (CARB), and the South Coast Air Quality Management District. Also reviewed were studies by the mechanical engineering departments at the University of Minnesota, Colorado School of Mines, and West Virginia University, as well as related congressional testimony and court records. Results have been compiled into a single report, The Cleaner Choice: Natural Gas as a Substitute for Diesel (GRI-99/0261).
New data also show that particulate emissions from diesel engines in heavy-duty vehicles consistently exceed certification standards. Data from a series of tests by the NREL and the Department of Energy show that diesel trucks with certified engines had average in-use PM emissions of 0.23 g/BHP-hr-more than twice the standard. Many trucks were emitting 0.4 to 0.6 g/BHP-hr by the time they had accumulated 200,000 miles. The NREL data show that actual average natural gas engine emissions were well below the standard for both buses and trucks.
The debate over emissions recently culminated in a lawsuit by the EPA, CARB, and the Department of Justice against seven major diesel engine manufacturers. The suit alleged that many of the emission-control devices on engines were designed to maintain low emissions during official emission tests while later advancing fuel injection timing under on-road driving. The suit also charged that these devices helped improve fuel economy and reduce soot contamination of oil during driving, but more than doubled nitrogen oxide emissions. In the largest legal settlement in the history of the Clean Air Act, manufacturers denied their AECDs were defeat devices, but agreed to eliminate them from future engines.
Natural Gas Engine Advantages As the analysis indicates, natural gas engines also can be designed to achieve very low nitrogen oxide emissions.
More than 60,000 natural gas transit buses, pickups, and vans already are in operation in the United States. Heavy-duty natural gas engine manufacturers have or are pursuing certification to CARB or EPA ultra-low emission vehicle standards. These engines will meet the 2004 heavy-duty engine standards. In addition, some heavy-duty natural gas engines have been certified to even lower nitrogen oxide levels under California's emission credit program.
Effect of Diesel Pollutants The GRI report summarizes data from studies on diesel pollutants and public health. Among the findings:
* Diesel engines are among the main sources of particulate matter. The EPA has found that this significantly increases the risk of diseases such as asthma and chronic bronchitis. In 1997, EPA established new National Ambient Air Quality Standards. The stricter standards were suspended by a federal court and criticized by the diesel industry as too strict.
* Preliminary results of a study by the South Coast Air Quality Management District of California indicate that 72% of the total cancer risk is attributable to diesel. Another 10% is due to 1,3 butadiene, 6% from benzene, and 12% from all other toxic air contaminants combined.
* CARB has classified diesel as a contaminant. Based on this data, EF&EE researchers calculate that the risk of lung cancer from exposure to diesel in California is about 540 cases per million people. However, EPA data show that this threat is only one of a number of risks. Other risks include pneumonia, asthma, and other respiratory diseases. The EF&EE study calculates that the lifetime risk of premature death from exposure to diesel exhaust in California is about 4,250 cases per million, or one person in 235.
The GRI report is available free of charge and can be ordered from the GRI Document Fulfillment Center, 1510 Hubbard Dr, Batavia IL 60510; or by fax at 630-406-5995.