Natural gas is primarily composed of methane (CH4), which, when burned, produces carbon dioxide (CO₂) and water vapor (H₂O) as its primary emissions. While CO₂ is a greenhouse gas, it produces less CO₂ per unit of energy compared to diesel fuel. Cummins estimate that up to 27% lower CO₂ emissions can be achieved. This results in lower carbon emissions when natural gas is used for power generation or as a transportation fuel.

Nitrogen oxides (NOx) are air pollutants that contribute to smog and acid rain. Natural gas engines produce lower NOx emissions compared to diesel engines because they burn fuel at a lower temperature, which reduces the formation of NOx. Diesel engines operate at higher temperatures which leads to the formation of NOx. This makes gas-fired engines a cleaner choice in terms of air quality.

Diesel engines emit particulate matter, which includes tiny particles and black carbon that can be harmful to human health and contribute to air pollution. In diesel engines, fuel is injected into the air in the combustion chamber and combustion may occur while fuel continues to be injected. This results in regions of high fuel concentrations where soot can easily form. Natural gas engines produce significantly fewer particulate emissions, improving air quality.

In addition to lower CO₂ emissions, natural gas has a lower greenhouse gas intensity due to the lower levels of methane leakage during production and transportation compared to other fossil fuels. Methane is a potent greenhouse gas, so minimizing its release is crucial for reducing the overall environmental impact of natural gas.