Exhaust emissions from a typical NGV are much lower than those from gasoline-powered vehicles. For example, the natural gas-powered Honda Civic is recognized by the U.S. EPA as the cleanest commercially available, internal-combustion vehicle on earth.  This Civic is rated by the California Air Resources Board as meeting the very stringent AT-PZEV standard.  In addition, dedicated NGVs produce little or no evaporative emissions during fueling and use. In gasoline vehicles, evaporative and fueling emissions account for at least 50 percent of a vehicle’s total hydrocarbon emissions.
Typical dedicated NGVs can reduce exhaust emissions of:
Carbon monoxide (CO) by 70 percent
Non-methane organic gas (NMOG) by 87 percent
Nitrogen oxides (NOx) by 87 percent
Carbon dioxide (CO2) by almost 20 percent below those of gasoline vehicles.
Natural gas vehicles also produce far less urban emissions than diesel vehicles.  For example, even when the stringent 2007 EPA heavy-duty engine emission standards become applicable, NGVs will be producing only one-sixth the NOx of comparable diesel engines.