The IIT Kanpur study has found alarming details on Delhi's air pollution, including the presence of polycyclic aromatic hydrocarbons (PAH), that are extremely toxic chemicals and a product of emissions from diesel-run vehicles among others.

Apart from PAH, the draft report, that has been submitted to the Supreme Court, identifies the sources of suspended particulate matter PM 2.5, namely road dust (38 per cent), vehicles (20 per cent), domestic fuel burning (12 per cent) and industrial point sources (11 per cent).

Anumita Roychowdhury, head of Centre for Science and Environment (CSE's) clean air campaign, said that even traces of PAH, which is anyway found in "very small quantity", can be extremely deadly and can reach harm to a foetus as well.

"PAH are toxic gases and a potent carcinogen, meaning exposure to them can cause cancer. It comes mainly from sources that use diesel as fuel which include diesel-run cars, gen sets, trash burning," she said.

The government has submitted the draft report of the study, that was commissioned in 2013, to the apex court. But it has not yet been made public.

Sources in the government expressed their "displeasure" over the report not being made public, which they said is resulting in it not getting public feedback and leaving room for speculations.

Pollution experts said that the presence of PAH is alarming also because it makes particulate matters such as PM 2.5 and PM 10, which are already present in large amounts in the city's air, more deadly.

"This is because these particles, which can embed themselves deep in the respiratory system, can carry with the toxic gases inside inflicting more harm," Roychowdhury said.

Apart from PM 2.5, the report has identified oxides of



Nitrogen (NOx) as the pollutant of concern in the city. Its main sources are industrial estates including power plants (52 per cent), vehicles (36 per cent), diesel generator sets (6 per cent) and domestic sources (3 per cent).

But if aircraft is excluded from the list of ground sources of pollution, vehicles emerge as the top NOx emitter according to CSE.

The draft report has also found variation in contribution of different pollution sources in winter and summer months. During winters, vehicles contribute to 25 per cent of PM 2.5 emissions, 26 per cent comes from biomass burning.

While during summers, coal and flyash contribute to 26 per cent of PM 2.5, soil and road dust 27 per cent, biomass burning 12 per cent, vehicles 9 per cent.

The report underscores that secondary particles, which adds to PM 2.5, called nitrates, formed by NOx and sulphate formed by SO2 are around 30 per cent in the winter months and 15 per cent during summer.

"Secondary particles are formed once gases such as SO2, NO2 are released in the air. Through atmospheric changes they turn into particles and add to the volume of suspended particulate matters," Roychowdhury explained.

The report of the IIT-K study titled 'Source Apportionment Study of PM2.5 and PM10', that was deliberated upon recently in a meeting attended by its lead investigator, has played a major role behind the recent announcement of a series of anti-pollution measures by the Delhi government.

It also recommends a switch to Euro VI emission compliant petrol and diesel. Incidentally, the city government announced its decision to adopt Euro VI by 2017 after receiving the report.

Euro IV fuels, currently in force in major cities, contain 50 parts per million (ppm) sulphur, while Euro VI stipulates 10 ppm sulphur. BS IV and BS VI are equivalents to the corresponding Euro fuels.