NGVs and the Environment

Overview

• 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.
• The actual emission benefits of introducing natural gas vehicles into a fleet will vary depending on the type of NGVs used and whether the emission comparison is based on the emissions of the vehicles being replaced or new motor vehicles.
• Fleets that replace in-use medium and heavy duty diesel vehicles with new natural gas vehicles will see the most significant reductions in emissions since medium and heavy duty trucks put out much more emissions than light duty vehicles.
• Medium and heavy duty natural gas engines that are retrofitted to repower an existing fleet were the first engines to satisfy the U.S. EPA’s demanding 2010 emission standards for nitrogen oxides.
• When used as transportation fuel, natural gas can reduce greenhouse gas emissions by 20 – 29 percent compared with diesel and gasoline fueled vehicles, respectively, according to studies by the California Air Resources Board and other organizations.

Emission Benefits
Exhaust emissions from NGVs are generally lower than those of gasoline and diesel powered vehicles. The natural gas-powered Honda Civic GX is recognized by the U.S. EPA as the cleanest commercially available, internal-combustion vehicle on earth.  The Civic GX is rated by the California Air Resources Board as meeting the very stringent AT-PZEV standard.  The Civic also has been awarded the title “Greenest Vehicle” for six consecutive years by the American Council for An Energy-Efficient Economy (ACEEE).

Compared to its companion gasoline Civic, the CNG powered Civic produces 95% fewer emissions of non-methane hydrocarbons, and 75 percent less emissions of nitrogen oxides – emissions that contribute to ozone formation. In fact, most available light duty NGV models have been certified to the Federal Tier 2, Bin 2 standard (only Bin 1, which requires 0 emissions, is more demanding).

While new natural gas fleets will see the most significant emission reductions, another effective strategy for reducing emissions is to repower or retrofit in-use medium or heavy duty vehicles with a natural gas engine. Medium and heavy duty natural gas engines have been certified to extremely low levels and were first to satisfy the U.S. EPA’s demanding 2010 emission standards for nitrogen oxides.

In the future, natural gas and diesel engines are expected to meet these demanding emission levels and likely will have similar emission profiles for criteria pollutants. However, in the next several years, some diesel engine manufacturers are expected to rely on credits to meet the more demanding emission levels.

Therefore, new natural gas engines should continue to provide additional nitrogen oxide reductions compared to many diesel engines for at least several years. In addition, research and development and use of newer emission control strategies should further improve the emission profile of new natural gas engines in the coming years.

Argonne National Laboratory has developed a calculator Link for Argonne National Laboratory Calculator: http://www.transportation.anl.gov/modeling_simulation/AirCred/index.html

to assist fleets that want to estimate the emission benefits of replacing existing fleet vehicles with light and heavy duty natural gas vehicles. This calculator shows that fleets can greatly reduce their overall emissions by replacing existing vehicles with natural gas vehicles.

According to this calculator, new natural gas vehicles provide the following benefits compared to in-use gasoline and diesel fueled vehicles.

The charts below are based on information prepared for the U.S. Department of Energy and California Energy Commission. The estimates compare new natural gas vehicles with new gasoline and diesel powered vehicles. The emission results include criteria pollutants and greenhouse gas emissions.

*For most air toxics

Greenhouse Gas Emissions in Greater Detail
Per unit of energy, natural gas contains less carbon than any other fossil fuel, and thus produces lower carbon dioxide (CO2) emissions per vehicle mile traveled. While NGVs do emit methane, another principle greenhouse gas, any increase in methane emissions is more than offset by a substantial reduction in CO2 emissions compared to other fuels. The California Air Resources Board (CARB) has conducted extensive analyses on this issue and it concludes that burning CNG produces about 68.0 grams of carbon dioxide equivalent emissions per mega joule (MJ) burned (this includes all methane emissions). Gasoline and diesel fueled produce approximately 94 – 95 grams of CO2 equivalent emissions per MJ. These comparisons are well documented by CARB and are based on well-to-wheel analyses.

The conclusion of recent studies such as those conducted by CARB and others is that, when used as transportation fuel, natural gas can reduce greenhouse gas emissions by 20 – 29 percent compared with diesel and gasoline fueled vehicles, respectively. In the future, these benefits could increase as natural gas supplies increasingly may be blended with renewable natural gas, commonly referred to as biomethane. Renewable natural gas reduces carbon emissions by almost 90 percent when compared with gasoline and diesel fuel. Therefore, blending conventional supplies of natural gas with renewable natural gas holds great promise of reducing greenhouse gas emissions.

CARB LCFS Carbon Intensity Reductions for Natural Gas: