Are natural gas cars green? A comparison about exhaust gases that busts a myth – A study

Not just particulates. CNG vehicles also produce large quantities of ammonia emissions, which are responsible for pollution

by Federico Coppini
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Are natural gas cars green? A comparison about exhaust gases that busts a myth – A study

No, methane used for mobility is not a green solution. The report of Transport and Environment, an association started 30 years ago in Brussels that brings together dozens of NGOs for sustainable mobility, dispels the myth that compressed natural gas (CNG) vehicles – commonly called "natural gas" – pollute less than petrol or diesel cars.

A commonplace so widespread that governments, including that of Italy’s, provide incentives and tax breaks for the purchase of CNG cars and local administrators allow access to historic centres and restricted traffic areas.

Suffice it to say that, in Italy, natural gas for motor vehicles is taxed 99.5% less than diesel, with an annual loss of public revenues of around €675 million. Very high number of polluting particles The Transport and Environment report, which is based on a series of laboratory tests, underlines how compressed natural gas cars emit on average between nine and 900 billion polluting particles per kilometre travelled.

These fine particles, being even smaller than those emitted by vehicles that run on other fuels, are even more dangerous for health. The hole in the legislative system is attributable to the absence of a legal limit on the number of particles emitted by CNG cars.

Limit that exists for petrol and diesel vehicles, but is not applicable to compressed natural gas engines due to the fineness of the emitted particles. This type of engine meets a legal limit only in relation to the mass of particulates.

However, this threshold is not very effective in controlling pollution due to the fineness of the particles. Ammonia emissions and serious diseases Not just particulates. CNG vehicles also produce large quantities of ammonia emissions, which are responsible for pollution.

Road tests on compressed natural gas cars and vans revealed ammonia emissions of up to 20 mg/km and 66 mg/km respectively. Even in this case, however, cars and vans are currently not subject to limitations in relation to ammonia emissions.

The high levels of toxic pollutants, can be read in the report, are connected to the onset of various serious pathologies such as cancer, Alzheimer’s, cardiovascular and respiratory diseases. “Natural gas buses also emit a lot of dust.

Generally,” as explained by the association, “in compressed natural gas vehicles there is a higher number of particles emitted during urban driving, or at low speeds, with cold starting. A particularly alarming figure for the air quality of cities and urban areas”.

Citizens for Air: Stop the contributions to methane According to these results, funding for the purchase of CNG vehicles appears inexplicable. Italy, as do the political strategies of the European Union, classifies compressed natural gas technology as a clean technology that uses sustainable fuel for transport.

Anna Gerometta, president of Cittadini per l'Aria – a non-profit organization which is part of Transport and Environment – underlines that “there is a link between the emissions of these cars and the formation of secondary particulate matter (Pm 2.5) in our cities”.

The correlation seems to be due to the dispersion of ammonia in the atmosphere caused by methane fuel. “To protect the health of citizens, these vehicles should be banned in urban areas and, of course, the purchase with contributions must not be promoted,” concludes Gerometta, “as, for example, the Municipality of Milan is about to do”.