NEW DELHI: The Delhi government may be targeting private vehicles to check rising air pollution levels, but a study by IIT-Kanpur shows that cars and jeeps contribute less than 10% of particulate matter while trucks are bigger culprits.A big contributor to Delhi’s air pollution is road dust that accounts for about 35% of tiny particles known as PM 2.5 in the air, followed by vehicles, according to a recent study by the Indian Institute of Technology, Kanpur.The other big contributors include domestic cooking, power plants and industries. Vehicle emissions account for an average of 25% PM 2.5 levels, going up to 36% in the winters.Trucks and two-wheelers account for larger chunks of PM 2.5 pollution than passenger cars’ contribution of 14-15% to overall vehicle emissions. ET reviewed the findings of the IITKanpur report, ‘Source Apportionment Study of PM 2.5 and PM 10’, which was submitted to the Delhi government late last month.This report, commissioned by the state government in 2013, is said to be one of the triggers for the Arvind Kejriwal government’s action plan to address air pollution concerns in the Capital.A top official in the Delhi government confirmed to ET the IIT-Kanpur study had indeed concluded that trucks are the major contributors to PM 2.5 pollution among vehicles."Road dust and construction dust are the biggest contributors to PM 10 and PM 2.5 as per the draft report from IIT-Kanpur — their contribution in PM 10 is up to 50%. In PM 2.5, trucks contribute the most among vehicles — up to 46%," the source said on condition of anonymity. The official said the state’s environment department was "actively deliberating" on the report but wanted the final findings to come out next week before planning "more specific" steps.With vehicles contributing up to 40% of secondary particulate pollution, a senior official at Delhi’s environment department said that it was important to target vehicular emissions."While road dust is a major contributor to high PM 2.5 levels in the city, it must be factored in that while this is true in summers, in winters road dust plays very little role in overall air quality. In this season it is clearly vehicles that are contributing the most — rising up to 35-36% contribution at times," the official said on condition of anonymity."In summers, dust levels are high and vehicular contribution goes down by 10% on an average," the environment official said.The person said overall pollution level goes up in winter also because of additional biomass burning for cooking as well as stubble burning in neighbouring states in November. PM 2.5 refers to fine particulate matter with diameter of 2.5 micrometres or less. This poses the greatest health hazard as it can enter the blood stream and also get lodged in the lungs.World Health Organization recommends that the level of these particles in the air should not be higher than 25 micrograms per cubic metre. Delhi has been recording very high PM 2.5 levels, regularly shooting up to ‘severe’ category, which indicates PM 2.5 levels of more than 250 micrograms per cubic metre.That vehicular contribution to deteriorating air quality is significant is also clear through analysis of the secondary particulates — which are there in the atmosphere as sulphur dioxide, nitrogen oxides, ammonia, and its compounds.The IIT-Kanpur study said that while vehicles contribute up to 40% to this category by way of emissions, the rest comes from power plants, industry and domestic sources besides area sources like crop burning.The report is learnt to have emphasised, however, that massive and concerted action across all contributory factors needs to be taken to help improve Delhi’s air quality. It has also been pointed out that for any strategy to succeed in countering air pollution in Delhi, the entire National Capital Region (NCR) and areas in the vicinity of Delhi will have to be actively engaged.There have been reports earlier in the media on parts of the IIT-Kanpur study. On November 27, The Times of India had published a report stating IIT-Kanpur has recommended that Euro VI fuel standards be introduced in Delhi at the earliest to check rising air pollution.The Delhi government on Wednesday also released the Delhi Statistical Hand Book 2015, which showed that the Capital had 88.27 lakh registered vehicles, including 27.91 lakh cars & jeeps and 56.81 lakh motorcycles & scooters, as of March 31, 2015.