India Environment Portal Knowledge for change

but why CNG?

• 14/03/2001

A study says particles emitted by diesel engines can harm the foetus, breaching the safety of the womb. Another study says the risk of developing cancer is four times higher among children travelling in a diesel bus as compared to someone travelling in a car in front of the bus.

The first study was published in the February 2001 issue of the reputed US journal Environmental Health Perspectives . Nobue Watanabe and Masayuki Kurita of the department of environmental health at the Tokyo Metropolitan Research Laboratory of Public Health in Tokyo, Japan, studied the effects of the diesel exhaust on the foetus. They noted adverse effects on the foetuses’ testis, ovary, and thymus gland (that produces growth hormones).

The second study was published in January 2001 by the Natural Resources Defence Council (NRDC), a US-based non-governmental organisation. It assessed the cancer risk to children from sustained exposure to diesel exhaust while travelling in school buses for 1-2 hours every day during a school year of 180-200 days over a period of 10 years. The council concludes that for every one million children, 23 to 46 children may eventually develop cancer from the excess diesel exhaust they inhale. This means that a child riding a school bus is being exposed to as much as 46 times the cancer risk considered “significant” by the US Environmental Protection Agency. It states that diesel exhaust levels are highest in the back of the bus as compared to the front and are highest when windows on the bus are closed. The study says one CNG bus achieves emission reductions equivalent to removing 85-94 cars from the road.

The report also says that ‘green’ diesel is not as clean as several US-based diesel engine companies claim: “The ‘green’ diesel engine will emit 1.6 to 1.7 times more oxides of nitrogen than its natural gas counterparts.” Studies on exhaust fumes from vehicles using the cleanest diesel available in the US revealed the presence of dioxins, some of the most powerful carcinogens known to humankind. It is important to stress that the diesel used in the US is far cleaner than what is used in Delhi.

What is already known
A 1997 study by the Centre for Science and Environment (CSE) revealed that at least one person died prematurely every hour in Delhi in 1995 due to only suspended particulate matter (SPM). A 1998 study at the All India Institute of Medical Sciences, New Delhi, showed how emergency visits and deaths due to respiratory and heart problems are the highest when particulate levels peak during winter. Asthma incidence increases by 900 per cent. The World Health Organisation says SPM can trigger bad health effects even at concentrations much lower than those considered safe. SPM levels in Delhi are already way above the limit. The levels of PM10 (particles 10 micron or smaller) in Ashok Vihar, a residential area in Delhi, reached 10 times the permissible limit in October 2000. These smaller particles are the most dangerous as they go deep into the respiratory tract.

As if that wasn’t enough, over 90 per cent of the particles in diesel engine exhaust are one micron in diameter or smaller (PM1). Improving diesel engines or diesel fuel to reduce particulate emissions leads to a larger number of smaller particles, even as the overall emissions come down. This means the better the engine and fuel quality, the greater the danger. PM1 isn’t monitored in Delhi. Moreover, the high levels of polycyclic aromatic hydrocarbons (PAHs) that coat diesel particles make them extremely carcinogenic. Which is why diesel particles have been classified as toxic air contaminants, not particles from the exhaust of petrol or CNG engines. Two of the strongest human carcinogens ever found are found in diesel exhaust (see graph: Cancer risk: the clean diesel myth ).

CNG is safer, cheaper
By moving to CNG, the emission levels of particulates can be brought down to levels lower than the Euro IV norms for diesel vehicles, which are to be implemented in Europe only in 2005 (see table: Quantum leap ).

The Supreme Court order literally leapfrogs Delhi by at least eight years. CNG also works out cheaper than diesel in the long run. A study by the National Institute of Public Finance and Policy (NIPFP) for the Union ministry of environment and forest concludes that CNG is a more cost-effective option for buses than particulate traps on current diesel buses or bringing in advanced diesel buses that need cleaner, costlier fuel. It estimates that the cost (per weighted tonne) of emission reduction with particulate trap is 60 times that of CNG conversion. The cost of retrofitment can be recovered in three years. The NIPFP study concludes that CNG retrofitment appears the “most cost-effective among the available options for Delhi.”