The findings were part of a study conducted by the National Environmental Engineering Research Institute.

An analysis of Delhi’s air pollution and future trends says that 60% of Delhi’s particulate matter pollution comes from neighbouring Haryana and Uttar Pradesh. Moreover, even if Delhi were to adopt the cleanest-grade fuel available, ensure that power plants in the vicinity adopt stringent emissions and ensure tidy pavements, pollution would persist well above globally-recommended safe levels, unless neighbouring states too adopted similarly stringent policies. Even if Delhi’s neighbours were to cooperate, it would at best halve Delhi’s pollution and still be short of the government-ideal of 40 microgram/cubic metre. This is because Delhi’s geographical location and land-use patterns are such that a fixed mass of particulate matter will persist. Delhi’s particulate matter pollution hovers between 300 and 900 microgram/cubic metre, depending on the weather.

The findings were part of a study conducted by the National Environmental Engineering Research Institute (NEERI), a CSIR body, along with researchers the Austria-based International Institute for Applied Systems Analysis (IIAS). Though these findings are yet to be peer-reviewed or published in a journal, they were discussed with officials at the Central Pollution Control Board at meeting on Wednesday. The researchers based their analysis on measurements of a range of sources of pollution — from burning biomass, vehicles, road-dust, cook-stoves — in Delhi. In their assessment, transport sector contributed nearly a fifth of the PM 2.5 — the ubiquitous residual particulate matter resulting from incomplete burning of matter — in Delhi. PM 2.5 is linked to respiratory diseases and cancer.

However, the scientists didn’t disaggregate the relative role of big diesel cars and transport vehicles in pollution cause by ‘transport.’ Other key sources, in Delhi include the burning of biomass in cooking stoves, secondary inorganic aerosols from power plants and ammonia from agriculture. Attributing the sources of pollution in Delhi has been a controversial exercise with different experts, over the years, disputing the relative role of agriculture waste, vehicles, industry and road dust in exacerbating air pollution. “The research identifies a range of measures...including road paving to reduce road dust emission, a rapid transition to clean cooking fuels in Delhi and neighbouring states and managing agriculture and municipal waste,” said Padma Rao, senior scientist at NEERI and a co-author of the report.

“Majority of Delhi’s pollution comes from outside with half from the surrounding states of Haryana and Uttar Pradesh, a quarter from sources even further away and a quarter from natural sources,” the authors said a in a press statement. “Even Pakistan is a contributor though there’s also pollution going out from India. We haven’t specifically modelled that,” Markus Amann of the IIAS, who led the study, told The Hindu.

The study finds that nearly a fourth of the 15,000 tonnes of PM2.5 emitted annually is due to road dust and about 40% due to power plants and residual and commercial combustion. Road transport, in this estimate, contributes about 16%. If Delhi were to continue on its growth trajectory, road dust and burning waste would together become the biggest sources of pollution—about half put- together-- by 2030, the NEERI analysis adds. The team arrived at their results through a modelling study—funded by the Department of Science and Technology—that accounted for the local meteorological conditions around Delhi, projected weather patterns into 2030, recorded traffic movement, as well as gauged emission patterns from commercial and private establishments. “Tackling the multiple sources of air pollution in Delhi…will not only reduce the estimated 8,900 premature deaths a year from air pollution in Delhi, but also cut the city’s greenhouse gas emissions,” said Amann.

Delhi is among the world’s most polluted cities. In 2014, it was ranked the most polluted globally in terms of PM 2.5, by the World Health Organisation (WHO). In a May-update by the WHO, Delhi was toppled by Zabol, in Iran. Gwalior and Allahabad, meanwhile, came a close second and third in terms of PM 2.5, while Patna and Raipur are ranked 6th and 7th.