A great drama is going on in Delhi for the last few days in the name of reducing air pollution. Diesel vehicles more than 10 years old and petrol vehicles more than 15 years old have been banned from plying on roads. Trucks are being prevented from entering the city. It’s a bolt from the blue for the hapless middle class Indian who took a loan to buy a second hand (used) car or the trucker who had no inkling of what was coming and was stumped by these orders.
The whole premise on which these orders have been passed are that diesel vehicles pollute more and the rapid dieselisation of Delhi personnel vehicles is the cause of pollution. Well, let’s put things in perspective. Both petrol and diesel vehicles burn distillates of crude and hence produce similar kinds of pollutants. The five main pollutants produced by a vehicle operated by an internal combustion engine are:-
- Nitrogen Oxides
- Suspended Particulate Matter.
Of these pollutants, diesel vehicles produce less Carbon-di-Oxide than petrol cars just by the virtue that they are more fuel efficient and hence burn less fuel per kilometre. Carbon-di-Oxide is the main cause for global warming also. Using a scale of 100 if petrol cars produce 100 Carbon-di-Oxide, diesels produce only 85.
Carbon-mono-Oxide causes heart diseases and affects stamina. If inhaled it can lead to death. Diesel engines do not produce Carbon-mono-Oxide while petrol engines produce it. Using a scale of 100, if petrol cars with catalytic converter produce Carbon-mono-Oxide equivalent to 42, diesels produce only 2.
Diesel engines produce more Nitrogen Oxides as compared to petrol. These gases form photochemical smog. If on a scale of 100, petrol cars with catalytic converter produce Nitrogen Oxide equivalent to 23, diesels produce only 31.
One of the main hydrocarbons produced by internal combustion engines is Benzene. It is carcinogenic, causes drowsiness and cough. Petrol cars produce much more Benzene than diesel. If on a scale of 100, petrol cars with catalytic converter produce Hydrocarbons equivalent to 19, diesels produce only 3.
As regards SPM, yes diesels produce much more of these particles as compared to petrol.
Another issue concerns the pollution when a vehicle is started and driven off. Also called the cold start pollution. This is a major concern in cities where a huge number of vehicles are started from cold. In case of petrol cars the time taken for the engine to warm up as well as the distance required for the catalytic converter to attain temperatures when they start reducing pollution is double the time and distance required for a diesel engine to heat up. Hence cars with petrol engines pollute for longer distances than those with diesel engines. Also it is notable that cars with catalytic converters are less fuel efficient than those without such converters and hence produce more Carbon-di-Oxide. Also, these cars are more polluting till the catalytic converter heats up.
In a normal drive, it takes about 10 km of driving to get the catalytic converter to temperature. With most commutes in city being less than 10 kms, the converter never reaches the temperature and hence these cars pollute more. Diesels have no such issues.
Studies by independent vehicle researchers TÜV Nord has revealed that Gasoline Direct Injection (GDI) petrol engines for cars emit more cancer-causing particles than modern diesel engines. GDI engines make petrol cars more fuel-efficient and reduce emission of Carbon-di-Oxide. However, findings indicate that these engines release around 1,000 times more harmful particles than traditional petrol engines and 10 times more than new diesels.
In Delhi, it is known that the main component of SPM is caused due to dust and construction activities and not due to diesel vehicles. Roads are not paved well, car parks are made mostly broken mud flats and there is incessant construction everywhere. Add to it the dust storms and the air of Delhi is a concoction of SPM. But, is that emissions from diesel cars? I don’t think so.