CNG and Pollution

By: Staff Reporter
With 1.1 million vehicles running on compressed natural gas (CNG), India has the 5th largest fleet of CNG vehicles in the world. However, CNG use only manages to reduce the particulate matter (PM) emissions as compared to other conventional fuels—on other counts however it performs poorly. Combined with the inability of the massive population of two-stroke auto rickshaw engines to adequately burn CNG, beseeches the government to re-evaluate their transport pollution control strategy.

CNG, a fossil fuel substitute for petrol, diesel and propane is widely considered a more environmentally ‘clean’ and safer alternative to conventional fuels—especially in the event of a spill wherein CNG can disperse quickly causing minimal environmental impact. In 1998, the Supreme Court of India ordered that all commercial passengers vehicles in the NCT of Delhi were to be converted to CNG, including taxis, buses and three-wheelers. After much controversy and protests, the shift happened, and the number of CNG vehicles in Delhi, Noida, Greater Noida and Ghaziabad today stands at over 6,75,000 (Indraprastha Gas Limited, The switch to CNG was accompanied by a retirement of old commercial vehicles and an increase in the number of buses. As per data published by Natural and Bio Gas Vehicles, Europe, there were over 16 million CNG vehicles by June 2012, which constituted 1.5 per cent of the total vehicles around the world. India occupies the fifth position with over 9 per cent of world’s CNG vehicles (Fig. 1, According to the ‘India CNG Vehicle Market Analysis Report 2013’ by RNCOS, an industry research solution outfit, the CNG kit’s market worth was around Rs 16 billion in 2011 and is likely to grow at a compound annual growth rate (CAGR) of around 22 per cent by 2014 to reach around Rs 30 billion by 2014.

Figure 1: NGV population in select countries - other than ships, trains and aircraft
Figure 1: NGV population in select countries – other than ships, trains and aircraft

How clean is CNG

The perception of CNG being a better fuel from the reduced emission perspective is not conclusively backed by evidence. A meta-analysis of emissions studies of various engine and fuel technologies for public transport vehicles, shows that there is no clear winner when it comes to fuel choice. Though the use of CNG lowers particulate matter (PM) emissions compared to conventionally used fuel and diesel, it performs badly on other emission components, particularly NOx, CO, CH4 which help in chemically producing ozone that results in photochemical smog in summers and acts as a greenhouse gas in the upper troposphere.  A Central Pollution Control Board’s 2011 study highlights that CNG is not without environmental drawbacks adding that burning CNG produces the highest rate of potentially hazardous carbonyl emissions. The study also made a case for regulating CNG and other fuels for methane emissions and revealed that retrofitted CNG car engines emit 30 per cent more methane. Thus, engine technology matters—and in a scenario where almost all CNG powered vehicles in India utilise retrofitted engines with regular petrol engines using CNG alternatives (Anumita Roychowdhury, (2010) ‘CNG programme in India: The future challenges’, Centre for Science and Environment), it is doubtful whether CNG is in any way negating the effects of vehicular pollution. A University of British Columbia study by lead author Conor Reynolds and his adviser, Milind Kandlikar, looked at the effects the CNG switch had on the levels of the greenhouse gases CO2 and methane, they found an increase in emissions leading to a 30 per cent rise in atmospheric warming caused by these gases. This is because the vehicles, most of which were retrofitted with CNG engines and fuelling systems, were less efficient, thus emitting more methane and CO2 than they did before. Aerosols (PM) are short-lived compared with greenhouse gases, their impact being more regional and the extent of their cooling and heating effects still quite uncertain. The study also finds that as much as one third of CNG is not properly burned in two-stroke engines, producing high emissions of methane as also substantial emissions of high particulate matter from unburned lubricating oil, which can appear as blue smoke—a hallmark of CNG auto-rickshaws. According to the researchers, the New Delhi’s programme could have achieved greater emission reductions at a cheaper price by simply upgrading two-stroke models to the cleaner, more fuel-efficient four-stroke variety. It is then perhaps time that our policies are reviewed and battery powered options sought. Beginning at the top, the much tainted politicians of the country can show the way by using battery powered vehicles in Lutyen’s Delhi and the Parliament precincts.  Senior officers would follow suit. With petrol, diesel and CNG vehicles regulated—being allowed to ply only on special arterial routes, Delhi’s environment would turn green in a space of two years or less.

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