Fifty shades of CNG

Published: September 22, 2013
Lahore has converted to CNG, but this isn’t always a good thing.

Lahore has converted to CNG, but this isn’t always a good thing.

Developing countries like Argentina are getting rid of their compressed natural gas (CNG) and switching to bio fuels. But Pakistan can’t seem to get enough of it — indeed, we are importing the CNG kits that Argentina is getting rid of. In fact, people here have switched over so rapidly to CNG that today we have the highest number of CNG vehicles in the world. But is this a good thing?

Researchers from the Sustainable Development Study Center at GC University, Lahore decided to compare how much pollution is emitted by fuel type. Their findings were just published in a report titled, ‘A Comparison of Engine Emissions from Heavy, Medium, and Light Vehicles for CNG, Diesel, and Gasoline Fuels’ appeared in the Polish Journal of Environmental Studies.

The experts checked how much sulfur dioxide (think acid rain), carbon monoxide, smoke, nitrogen monoxide and hydrocarbons were produced. They were worried because Lahore has an estimated five million vehicles.


As it turns out, using CNG is generally good but only depending on the type of vehicle. “It is not as clean as people think,” cautioned Dr Abdullah Yasar, the primary author of the paper. It tends to produce some emissions more than diesel and gasoline.

So for example, when heavy vehicle engines switched from diesel to CNG, their harmful emissions went down. The same happens when diesel cars start using CNG. But when cars on gasoline start using CNG, they ended up producing more harmful nitrogen monoxide. The experts found the same problem with 4-stroke CNG rickshaws — they produced more nitrogen monoxide than a gasoline rickshaw.

The experts also found that CNG engines produced nine to 20 times of another harmful gas, carbon monoxide, than diesel engines. For example, the CNG van engine added 8.7 times carbon monoxide to the air compared to the diesel van engine.

The problem is that CNG engines work at temperatures that convert the atmospheric nitrogen gas to nitrogen monoxide.

Lahore’s vehicle population is 5m

Aside from these technical aspects of using CNG, experts like Dr Yasar are concerned about the stay orders CNG stations have acquired in Lahore to operate in residential areas. “In many cases they share walls with schools,” he said, citing hazards in cases of explosions.

For now, though, despite shortages, it seems that Pakistan can’t seem to kick its CNG habit. The future is, according to Dr Yasar, hydrogen gas that is being tested in Japan. “For the last 20 years or so they have been making prototypes and testing for safety,” he said. And if it works out, well, all our cars will produce is steam. 

Published in The Express Tribune, Sunday Magazine, September 22nd, 2013.

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Reader Comments (3)

  • Ad
    Sep 22, 2013 - 3:43PM

    This article is not accurate. Hydrogen is still a decade away from mainstream consumption. As far worldwide research is concerned, CNG still is far more environmentally friendly than petrol.


  • Jibreel Sohail
    Sep 22, 2013 - 6:54PM

    @ Ad

    CNG might be GLOBALLY environmentally friendly, not LOCALLY as the article shows.

    CNG is globally environmentally friendly because it produces the least amount of carbon oxides ( CO and CO2) than all the other fuels. But as the article clearly shows, the amount of proportionate more harmful gases produced (Carbon Monoxide, Sulphur Dioxide etc are a LOT MORE dangerous for human health than Carbon Dioxide) are either increased or little affected depending on the type of the vehicle.

    The article looks at the effect on the local environment of the city – Lahore, and it is completely accurate as far as that is concerned. CNG is no different than any other fossil fuel giving off pollutants into the city’s atmosphere on burning.


  • naeem khan
    Sep 22, 2013 - 8:36PM

    the only reason is cng is far cheaper than gasoline thats why people use it


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