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The increasing demand for diesel cars on the back of rocketing petrol prices could take more of a toll on your health than it does on the environment.
The differential pricing has had a distorting effect in the past few years. According to figures from the Society of Indian Automobile Manufacturers, diesel vehicles made up nearly 60% of the two million cars sold in the last fiscal year. In previous years, they have been less than 30% of the total number of cars sold annually. A litre of diesel costs Rs.40.91, while a litre of petrol costs Rs.71.92 in Delhi.
“In general, diesel exhaust has a much higher proportion of fine particulate matter than petrol. These are absorbed by our respiratory systems and are associated with an increased risk of cardiovascular diseases as well as cancer,” said Anumita Roychowdhury of the Centre for Science and Environment (CSE), an activist organization.
In comparison, emissions from petrol engines contain much less particulate matter, although the engines themselves aren’t as efficient as diesel ones, thereby directly adding to the atmospheric greenhouse gas content.
While carbon dioxide and carbon monoxide (CO)–components of vehicle exhaust–are also detrimental to health, there’s no easy method to gauge toxicity relative to particulate matter, though several studies are unambiguous about the latter’s harmful effects.
A study by Jay Shanker Pandey, a scientist at the National Environmental Engineering Research Institute in Nagpur, shows that the health risk posed by NO2 (nitrogen dioxide, common to both petrol and diesel exhaust) and particulate matter is 22.11 and 16.13 times more, respectively, than that of SO2 (sulphur dioxide), a key chemical compound strictly regulated by government emission norms and found in petrol engine emissions.
Other experts, however, said it wasn’t necessarily true that a greater proportion of diesel cars would mean a commensurate increase in health risks.
“Sure, diesel has more harmful, particulate matter but their emissions also depend on average vehicle speeds, a vehicle’s idling time, the local environment where these gases are burnt,” said Sagnik Dey, who researches environmental pollution at the Indian Institute of Technology, Delhi. “So there could be a difference in the way it affects a particular population. Most studies on particulate matter are based on international studies.”
A diesel engine is more fuel-efficient than a petrol one, which is why it’s able to keep CO levels low in the first place. This is because during the combustion, there is little or no residue of unburnt carbon particles, which react with air to produce CO. But at the same time, this process wears down the fuel injection system, resulting in the generation of suspended particulate matter (SPM).
CSE’s Roychowdhury admits that diesel engines are more efficient, but said that “a litre of diesel emits more carbon dioxide than a litre of petrol when burnt”.
“Low diesel prices, an increase in large-sized diesel engines and now sheer number of such cars suggest that they could be playing an increasingly greater role in global warming,” she added.
However, the efficiency of the engines doesn’t mean that they are always less polluting than the petrol ones. A recent study by the Automotive Research Association of India (Arai), an autonomous body, says that a Euro III diesel car emits 7.5 times more particulate matter and three times more NO2 than a similar petrol car. However, the same diesel car emits 1.5 times less carbon dioxide, the most pervasive of the greenhouse gases.
Most of India’s diesel vehicle engines are based on European standards and typically follow emission norms on the continent, which trail those of the US. For instance, US Environmental Protection Agency (EPA) norms have capped emission levels, irrespective of the type of engine.
Bharat Stage III and IV, the emission norms followed in India that are modelled on European emission norms, have different rules for petrol and diesel engines. Thus, a Euro III diesel engine, for instance, is allowed to emit far more NO2 than a similar capacity petrol engine.
Though recent advances in diesel technology, such as diesel particulate filters, are available in the international market, they require so-called ultra-clean diesel, which is currently defined as containing less than 10 parts per million (ppm) of sulphur. The Euro III norms that are currently in force in 13 major cities of India use diesel with sulphur concentration ranging from 350 to 550 ppm.
Oil refineries say that without government help, the costs of refining diesel to those levels would be substantial.
“I can’t give you figures, but it would be a big amount, which would ultimately have to be passed on to society,” said R.K. Malhotra, research and development head at Indian Oil Corp. Ltd. Malhotra’s contention is that all blame can’t be passed on to the oil companies because it’s the government’s job to ensure that retrofit technologies, which are available internationally, be either bought or developed within the country and implemented.
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