With pollution rising to hazardous levels, Stage IV of the Graded Response Action Plan (GRAP) has come into effect in Delhi and adjoining National Capital Region (NCR) districts. Under these anti-pollution measures, diesel light motor vehicles as well as the entry of trucks into Delhi have been banned.
According to an order issued by the Commission for Air Quality Management (CAQM), BS-VI vehicles and those used for essential and emergency services will continue to ply the roads of the NCR region.
The ban will affect three lakh diesel light motor vehicles in Delhi that are not BS-VI compliant, reports Indian Express.
Moreover, all Delhi-registered diesel medium- and heavy-goods vehicles also cannot ply, with exemptions for those involved in essential or emergency services, Indian Express reports.
The step has been taken as vehicular emissions remain one of the top contributors to pollution in Delhi.
What are BS-VI norms set for vehicles? How harmful are diesel engines and how do they compare with petrol vehicles? We take a look.
BS-VI norms
BS or Bharat Stage emission standards are norms notified by the Centre to “regulate the output of air pollutants from internal combustion engine and spark-ignition engine equipment, including motor vehicles”, as per Business Standard.
The central government had made it compulsory for automakers to manufacture, sell and register only BS-VI (BS6) vehicles from 1 April 2020.
Under these norms, petrol vehicles have to be 25 per cent cleaner by decreasing NOx (Nitrogen Oxide) emissions from 80 mg/km to 60 mg/km.
“For diesel cars, the BS-VI norms aim at reducing three pollutants which include HC (Hydrocarbons) + NOx (nitrogen oxides), PM (Particulate Matter) and NOx reduction by 43, 68 and 82 per cent respectively,” Dr Partha Datta, president and managing director, FCA India, wrote for Times of India (TOI) in 2020.
Diesel vs petrol vehicles
Both petrol and diesel engines turn chemical energy into mechanical power by burning fuel but in different ways.
Diesel engines consume less fuel and are more efficient than their petrol counterparts.
Diesel contains marginally more carbon (2.68 kg CO?/litre) than petrol (2.31kg CO?/litre).
However, overall carbon dioxide (CO?) emissions are lower in diesel cars as compared to petrol vehicles, notes The Conversation.
According to TOI, while petrol engines have spark plugs to burn the air-fuel mixture, diesel depends on heavily compressed air without any spark plugs.
Diesel vs petrol engines. Graphic: Pranay Bhardwaj
Datta writes for TOI that “in diesel engines, air is very heavily compressed, typically to around 14 to 23 times its original volume, while in petrol engines, the compression ratio is generally much lower (typically seven to ten, with high performance compression ratios of up to 13).”
Diesel engines emit higher levels of particulate matter (PM)- tiny bits of soot residue from the combustion process, as per The Conversation.
Catalytic converters which oxidise pollutants such as CO to less harmful gases like CO? have greatly reduced emissions from petrol cars.
“Diesel fuel contains no lead and emissions of the regulated pollutants [carbon monoxide, hydrocarbons and nitrogen oxides] are lower than those from petrol cars without a catalyst. However, when compared to petrol cars with a catalyst, diesels have higher emissions of NOx and much higher emissions of particulate matter,” as per the Air Quality.org website.
Emission of hydrocarbons, carbon monoxide and lead pollution is lesser in diesel vehicles than in petrol.
However, diesel cars emit more noxious gases and ‘significantly’ more particulate matter (PM)2.
When compared to a diesel engine, petrol cars “produce virtually no particulate matter”, notes UK’s Air Quality.org.
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Adverse health effects
High levels of particulates can lead to several health issues such as cancer and acute respiratory effects.
Dr Matthew Loxham, a research fellow in air pollution toxicology at the University of Southampton, told BBC in 2018 that the most hazardous is the “smallest, so-called ‘ultrafine’ particles”.
Vehicular emissions remain one of the top contributing factors to pollution in Delhi. PTI (Representational Image)
“They get so deep into the lungs, they get to the surfaces where oxygen enters our blood, and the particles themselves almost certainly can enter the blood,” he said.
“They can cause increased stroke rates and increase heart attacks in people who are most susceptible, who have underlying health conditions,” Loxham elaborated.
According to BBC, if someone is exposed to nitrogen dioxide in the long run, it can affect lung function, enhance the risk of respiratory diseases and increase allergic reactions.
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Is diesel always more polluting?
It is complicated.
Modern diesel engines are cleaner as they emit fewer particulates because of being equipped with special filters.
“Modern diesels essentially do not have a particulates problem,” Emissions Analytics founder and chief executive Nick Molden told BBC in 2018.
“The filters clean up 99 per cent of the particles. So long as they are not tampered with, they are very effective”, he added.
Partha Datta notes that for BS-VI compliant diesel vehicles particulate limits have been set from 25 mg/km to 4.5, which is the same as for petrol engines.
Thus, particulate emission for BS VI diesels is equivalent to petrol vehicles, TOI cited him as saying.
With inputs from agencies
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