If you have noticed, diesel powered vehicles are always mentioned when a new order is passed for curbing air pollution in the country. Most recently, the Delhi government banned the entry of diesel powered transport vehicles (which means virtually every goods carrier) from entering the national capital in an effort to curb the smoggy conditions.

So, shall we simply assume that petrol vehicles release lesser amount of pollutants? Let’s do a fact check and find out.

Raw Material Used

Both petrol and diesel are made from crude oil, which is a mix of hydrocarbons. While raw crude oil can be combusted to produce energy, the difference inthe boiling points of various hydrocarbons means any combustion that happens will be uneven. To overcome this, the crude is refined to produce different varieties of hydrocarbons.

So, petrol and diesel are also a type of hydrocarbons. Petrol being the lighter variant, typically having chains of nine carbon atoms whereas the heavier diesel has chains of fourteen carbon atoms. Therefore, petrol is a more refined hydrocarbon, and diesel a more powerful one.

But, the longer carbon chains that enable diesel to deliver more power and mileage, also increase the chance of other elements such as sulphur and nitrogen being attached to the carbon chain. That is the reason behind diesel having more sulphur content than petrol, hence causing greater pollution.

Compounds Produced Upon Combustion

Petrol produces carbon monoxide and nitrous oxide upon combustion. The carbon monoxide then mixes with oxygen and becomes carbon dioxide, which is then released by the exhaust system of a petrol vehicle. On the other hand, diesel produces higher amounts of nitrous oxides along with sulphurous compounds in form of particulate matter when combusted.

Carbon dioxide is a greenhouse gas that is responsible for causing global warming. Nitrous oxides and particulate matter are responsible for health and growth issues in humans, animals and plants, hence posing more immediate danger.

The Myth or Reality of ‘Dirtiness’ of Diesel

Diesel technology has come a long way in the past few decades, mainly due to the huge R&D investment done in the technology after concerns arose over global warming in the 1990s. A Bharat Stage-I Diesel engine which was produced 15 years ago in India is up to 50 times more polluting than the Bharat Stage-IV Diesel engines in production today.

Contrary to that, petrol engine technology has progressed at a much slower pace and hence there is little difference between the emission indexes of different generation of these engines.

Furthermore, the quality of diesel in India is also an issue. Higher sulphur content means the vehicle, regardless of its engine refinement, is more polluting than it should be.


While the diesel engines from BS-I and BS-II era should be taken off from the Indian roads, immediately, the case for later diesel engines is much stronger. Newer Diesel engines are on par with modern petrol vehicles when it comes to air pollution. Also, improvement in fuel quality (both petrol and diesel) remains critical for the success of newer emission control norms.

Air pollution remains a major hindrance in the path of India’s development. People in metro cities are already switching to smart home technologies such as home air purifiers and office air filtration systems. The stagnant traffic conditions in most Indian metros have also prompted the use of Car Air Purifiers in the country. While these technologies are playing an important part in our health and well-being for the foreseeable future, the need for a collective action against air pollution remains as urgent as ever.

To know more about air purifiers and the technologies involved, click here.