Natural Gas Vehicle Emissions
Compared with vehicles fueled with conventional diesel and gasoline, natural gas vehicles can produce significantly lower amounts of harmful emissions such as nitrogen oxides, particulate matter, and toxic and carcinogenic pollutants as well as the greenhouse gas carbon dioxide.
Light-Duty Vehicle Emissions: CNG vs. Gasoline
Testing has been performed to compare the emissions of light-duty CNG vehicles versus light-duty gasoline vehicles. For detailed results, see the Vehicle Technologies Emissions Testing page.
As automakers have improved the emissions performance of gasoline vehicles to keep pace with stricter emissions regulations, improvements in CNG vehicles have kept their emissions performance ahead of the pack. The U.S. Environmental Protection Agency has called the natural gas Honda Civic GX the cleanest internal-combustion vehicle on Earth. Visit the U.S. Department of Energy/U.S. Environmental Protection Agency Fuel Economy Guide to compare the Civic GX with other cars for environmental impact and petroleum savings.
Heavy-Duty Vehicle Emissions: CNG & LNG vs. Diesel
Testing has been performed to compare the emissions of heavy-duty natural gas vehicles (fueled with CNG or LNG) versus heavy-duty diesel vehicles.
Transit buses equipped with model year 2004 CNG engines produced 49% lower nitrogen oxides emissions and 84% lower particulate matter emissions versus transit buses equipped with model year 2004 diesel engines. Nitrogen oxides and particulate matter are the primary emissions of concern for heavy-duty vehicles. For detailed results, see Emission Testing of Washington Metropolitan Area Transit Authority (WMATA) Natural Gas and Diesel Transit Buses.
In a study of CNG and diesel United Parcel Service (UPS) delivery trucks, CNG trucks produced 75% lower carbon monoxide emissions, 49% lower nitrogen oxides emissions, and 95% lower particulate matter emissions than diesel trucks of similar age. See United Parcel Service (UPS) CNG Truck Fleet: Final Results.
City of Los Angeles Bureau of Sanitation LNG Heavy-Duty Trucks recorded a 23% reduction in nitrogen oxides emissions from dual-fuel LNG refuse trucks compared with diesel trucks. In an evaluation of freight trucks, CNG trucks produced 24%-45% lower nitrogen oxides emissions and more than 90% lower particulate matter emissions compared with diesel trucks. See An Emission and Performance Comparison of the Natural Gas C-Gas Plus Engine in Heavy-Duty Trucks: Final Report.
The U.S. Environmental Protection Agency calculated the potential benefits of LNG versus diesel based on the inherently cleaner-burning characteristics of natural gas, summarized in Clean Alternative Fuels: Liquefied Natural Gas.
- Produce half the particulate matter of average diesel vehicles
- Significantly reduce carbon monoxide emissions
- Reduce nitrogen oxide and volatile organic hydrocarbon emissions by 50% or more
- Potentially reduce carbon dioxide emissions 25% depending on the source of the natural gas
- Drastically reduce toxic and carcinogenic pollutants
- Increase methane emissions (not a benefit)
To perform more in-depth analyses of alternative fuel versus conventional fuel emissions, see the AFDC Natural Gas Emissions page.