NGVs and the Environment
- Natural gas is the cleanest burning alternative transportation fuel commercially available today.
- Natural gas primarily consists of methane (around 90%), with small amounts of ethane, propane and other gases. Methane is the simplest hydrocarbon molecule made up of one atom of carbon and four of hydrogen (CH4). It is lighter than air and burns almost completely, with by-products of combustion being carbon dioxide and water.
- Among the regulated pollutants that affect urban air quality are nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOCs). VOCS and NOx combine with sunlight to form ground-level ozone or smog.
- 112 million Americans living in areas with air that is unhealthy to breathe; 100 million live in areas that fail to meet the air quality standards for ground-level ozone.
- On-road vehicles contribute more than 60 percent of all CO pollution and are the second largest source of VOCs (29 percent) and NOx (31 percent). In many urban areas, vehicles are the single largest source of these key criteria pollutants.
- Diesel fuel is of special environmental concern. Diesel exhaust includes over 40 substances that are listed by the U.S. EPA as hazardous air pollutants and by the California Air Resources Board (CARB) as toxic air contaminants – including benzene, 1,3-butadiene, and arsenic.
- Compared with most gasoline-powered vehicles, dedicated NGVs typically reduce exhaust emissions CO by approximately 70 percent, VOCs by 89 percent, and NOx by 87 percent, and produce negligible amounts of toxic air contaminants.
- Since they have a sealed fuel system, NGVs have virtually no evaporative and running loss emissions and negligible refueling emissions.
- The natural gas-powered Honda Civic GX is recognized by the U.S. EPA as the cleanest commercially available, internal-combustion vehicle on earth. It produces less urban emissions than the Civic gasoline-hybrid. In certain areas of the country, the exhaust from a Honda Civic GX actually is cleaner than the ambient air.
- Many chemical compounds found in the Earth’s atmosphere act as “greenhouse gases.” These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is reflected back towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere.
- According to the U.S. EPA, 82 percent of the anthropogenic (man-made) greenhouse gases are carbon dioxide (CO2).
- All else equal, the more carbon in a fuel, the more CO2 is produced.
- A natural gas molecule has about half the carbon of a gasoline or diesel molecule.
- Methane also is a greenhouse gas (and, in fact, is a more intense greenhouse gas than carbon dioxide). But even accounting for methane, NGVs produce 20 percent less greenhouse gases than a comparable gasoline vehicle and up to 15 percent less than a comparable diesel vehicle.
- Where NGVs are powered by biomethane (i.e., methane produced from renewable sources like landfills, sewage and animal or crop waste), the greenhouse benefits are much, much greater.
- Gasoline and diesel fuel is one of the most serious groundwater contamination sources. These petroleum products enter the groundwater supply a number of ways – including from leaking underground storage tanks at fueling stations and when tanker trucks overturn on the road.
- Since natural gas is lighter than air, any leaks that do occur do not enter the groundwater system and do not contribute to groundwater contamination.
- There have been a great many studies done over the years comparing the emissions from NGVs to comparable gasoline or diesel vehicles.
- For example, a recent (December 2005) study sponsored by the National Renewable Energy laboratories compares emissions and performance of diesel and natural gas transit buses (“Emission Testing of Washington Metropolitan Area Transit Authority Natural Gas and Diesel Transit Buses,” National Renewable Energy Laboratory, December 2005).
- Unfortunately, since both NGV and gasoline and diesel engine technologies have evolved significantly, most of these studies are only of historical value.
- To get information on more current studies of greenhouse gas comparisons, go to the Argonne Laboratories “Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation” model (GREET)
- To get more information on how EPA compares emissions, go to EPA MOBILE Model & Emissions Factors.