Happy Air Quality Awareness Week! Read Up How Alt Fuels Helps to Lower Emissions!

    Currently, the U.S. Environmental Protection Agency (EPA) requires all 2010 and newer engines and vehicles to meet the same emissions standards, regardless of fuel type. Even though this standard is in place for all newer engines and vehicles, most alternative fuel vehicles (AFVs) provide greater reductions in tailpipe and greenhouse gas (GHG) emissions when compared to petroleum-powered vehicles; including the emissions: nitrogen oxides (NOx), volatile organic carbons (VOCs), and ozone (O3).

    All-electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs; when in all-electric mode) produce zero tailpipe emissions. When using the internal combustion engine, PHEVs produce tailpipe emissions, such as NOx and VOCs.  Although, these emissions are typically lower than those of comparable petroleum-powered vehicles. EVs and PHEVs may produce well-to-wheel emissions (emissions measured as a sum of the fuel’s entire life cycle) depending on the source of electrical power used to charge the battery, such as a power plant.

    Biodiesel also offers tailpipe GHG emissions benefits compared to petroleum diesel. The GHG emissions benefits of biodiesel are especially significant because the carbon dioxide (CO2) released during fuel combustion is offset by the CO2 captured by the plants from which biodiesel is produced. However, biodiesel does slightly increase NOx emissions. Though the integration of sophisticated engine controls—as well as fueling and exhaust after-treatment devices—are the determining factors governing how clean a vehicle or engine will be.

    As with conventional fuels, the use and storage of ethanol blends can result in emissions of regulated pollutants, toxic chemicals, and GHGs. Emissions of primary concern from ethanol include hydrocarbons, NOx, carbon monoxide (CO), air toxics, and CO2. However, when compared to gasoline, the use of high-level ethanol blends, such as E85, generally result in lower emissions levels, including NOx and VOCs.

    Because natural gas is a low-carbon, clean-burning fuel, using natural gas can result in substantial reductions of hydrocarbon, CO, NOx, and GHG emissions. Natural gas vehicles can provide emissions benefits—especially when replacing older conventional vehicles or when considering life cycle emissions.

    Propane is also an inherently clean burning fuel due to its lower carbon content. When used as a vehicle fuel, propane can offer life cycle GHG emissions benefits over conventional fuels, depending on vehicle type, and drive cycle. In addition, using propane in place of petroleum-based fuels may reduce some tailpipe emissions. Emissions from propane vehicles are comparable to those of gasoline and diesel vehicles with modern emissions controls. Propane is frequently used to replace gasoline in smaller applications, such as forklifts and commercial lawn equipment. Because propane is a low-carbon fuel, a switch to propane in these applications can result in substantial reductions of hydrocarbon, CO, NOx, and GHG emissions.

    Please note, that O3 is a GHG that is not a direct vehicle emission; it is formed in the air through reactions of NOx, VOCs, and atmospheric air in the presence of sunlight. As such, AFVs that reduce NOx and VOCs can reduce the formation of O3. Generally, O3 formation in urban areas is more VOC-sensitive, while it is more NOx-sensitive in rural areas.

    For more information on AFV emissions, please refer to the following Alternative Fuels Data Center (AFDC) pages:

    ·         Emissions from Hybrid and Plug-in Electric Vehicles        (

    ·         Biodiesel Vehicle Emissions (

    ·         Ethanol Vehicle Emissions (

    ·         Natural Gas Vehicle Emissions (

    ·         Propane Vehicle Emissions (

    You may also be interested in the Argonne National Laboratory’s (ANL) Alternative Fuel Life-Cycle Environmental and Economic Transportation (AFLEET) Tool ( to calculate and compare the emission reduction benefits of AFVs compared with conventional vehicles. Instructions for using the AFLEET Tool are available here: For further information on how to use the AFLEET Tool, you can also view the Clean Cities webinar on how to use the AFLEET Tool, located on the Clean Cities Webinar Archives page (

    Additionally, you may also refer to the AFDC’s Petroleum Reduction Planning Tool ( This tool is a simple calculator for annual petroleum and GHG reductions. In particular, you may use the “Replace Vehicles” simulation to compare the annual GHG reductions associated with switching fleet vehicles from conventional fuels to alternative fuels.

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