Natural gas vehicles provide air quality benefits. Natural gas trucks and buses reduce both smog-related emissions as well as toxic emissions that affect human health. During vehicle refueling, there are no evaporative emissions as the connection between the fuel dispenser and the vehicle creates a sealed system. Highway tractors that operate on liquefied natural gas (LNG) incorporate boil-off capture systems, so that if LNG starts to warm up and return to a gas state, the fuel is captured and stored on the vehicle.
In the past, natural gas vehicles produced significantly lower levels of air pollutants compared to diesel vehicles. Natural gas had inherently lower levels of particulate matter (PM) that affects air quality and human health. Natural gas also produced lower levels of smog-related oxide of nitrogen (NOx) emissions. For this reason, the State of California encouraged greater use of natural gas in transit buses and in public fleets. Similarly Canada developed the world’s first natural gas transit bus in Hamilton, Ontario, in response to poor air quality due to local industrial activity.
As a result of the introduction of the 2007 and 2010 diesel emission standards that significantly limit both PM and NOx emissions, natural gas and diesel medium and heavy vehicles now have similar tailpipe emissions. Natural gas continues to provide other air quality benefits related to pollutants that are not covered by emissions standards, such as emissions of smog-related sulphur dioxide (SO2) and non-methane hydrocarbons (NmHC). Natural gas also contains no air toxics that are harmful to human health such as benzene, 1, 3 butadiene, or acetaldehyde.