Natural gas vehicles (NGVs) have a deserving reputation for being one of the cleanest transport fuels available, not just with respect to vehicle emissions, but also for fuel production. Studies around the world consistently show that natural gas engines produce fewer harmful emissions than petrol, diesel or LPG, in spite of the considerable improvements made to these fuels in recent years. Even when measured against other ‘clean’ fuels or methods, such as gasoline-electric hybrids, NGVs emissions are frequently lower.

The world’s cleanest internal combustion production line car is an NGV – the Honda Civic GX, available in the US. It has a dedicated engine which is reported in high polluting areas to produce exhaust emissions that are cleaner than the air going into the engine! The Civic can drive from the West Coast of the United States to the East Coast and emit less non-methane hydrocarbons than if you were to spill one teaspoon of petrol! (click on the picture to visit the Honda website for more info)

As diesel and petrol engine technology improves, so too does NGV technology, which means that NGVs are consistently ‘ahead of the game’ in terms of emissions.

Apart from producing fewer emissions, natural gas also poses fewer environmental hazards than other fuels. In the event of an accident, natural gas dissipates into the atmosphere rather than spilling on to the ground – a major benefit for our waterways and wildlife.

Emissions, what are they?

The main emissions currently regulated throughout the world are:

Carbon monoxide (CO) – Carbon monoxide is a gas that in high concentrations can lead to asphyxiation.

Particulate matter (PM) – Particulates are any materials that are trapped by a gauze filter during emission testing. This means not only is it a measure of soot particles but also liquid aerosols that have been trapped. Particles from any source that enter the lung can often cause lasting damage. In addition, particles that are highly reactive are believed to cause further damage. Obviously the best thing is have the fewest particles possible to reduce any risk as much as possible.

PM emissions have been the key focus of recent international emission standards.

Nitrogen oxides (NOx) – These are one of the constituents of photochemical smog/haze. In many areas it is the amount of NOx that is released that governs air quality. This is because there is already a large amount of HC in the air ready to react with the NOx. NOx has also been the key focus of recent international emission standards.

Hydrocarbons (HC), sometimes excluding Methane (NMHC) – As mentioned above HCs react with NOx to form smog/haze. As methane is a ‘non-reactive’ hydrocarbon, it is not involved in this smog forming process. When NGVs are discussed, the methane emission is usually excluded from the air quality measuring process.

‘Greenhouse’ gas emissions – As CO2 is generally the predominant greenhouse gas, greenhouse emissions factors are usually quantified in CO2 equivalents (CO2e). As methane is also a greenhouse gas, any unburnt methane emissions are usually included in NGV greenhouse emissions calculations. Due to the increasing efficiency of natural gas engines, this problem is progressively being minimised.