Greenpeace's report, titled 'Airpocalypse,' says Delhi is India's most polluted city.

The report is based on information obtained through online reports and Right to Information applications from State Pollution Control Boards across India, and assessments of air quality performed in 168 cities across 24 states and Union Territories. It claims that none of the 168 cities assessed complies with air quality standards prescribed by the World Health Organization (WHO).

It says the number of deaths in India caused by air pollution is only a "fraction less" than the number of deaths caused by tobacco usage, and adds that three per cent of the GDP is lost due to air pollution.

"We are facing an apocalypse right now due to unbreathable air, deaths due to air pollution are only a fraction less than those due to use of tobacco yet authorities are laying a deaf ear to the numerous scientific reports that have set alarm bells ringing," said Sunil Dahiya, campaigner, Greenpeace India.

Greenpeace's report says only a "few" cities in southern India comply with air quality standards prescribed by the Central Pollution Control Board (CPCB), and pinpoints fossil fuels as one of the "main culprits" for the deteriorating air quality across the country.

"The top 20 most polluted cities have PM 10 levels between 268 g/m3 and 168 g/m3 for the year 2015. While, Delhi tops the list with 268 g/m3, it is followed closely by Ghaziabad, Allahabad, and Bareli in Uttar Pradesh; Faridabad in Haryana; Jharia in Jharkhand; Alwar in Rajasthan; Ranchi, Kusunda and Bastacola in Jharkhand; Kanpur in Uttar Pradesh; and Patna in Bihar with PM10 levels ranging from 258 g/m3to 200 g/m3," the report explains

The assessment of air pollution levels for Delhi highlighted that PM10 concentrations are 268 g/m3 for the year 2015, which are 4.5 times higher than the National Ambient Air Quality Standards (NAAQS) annual limit set by CPCB, and about 13 times the annual limit set by WHO for PM10.

Detailed observation of the data suggests that PM10 levels have been very high throughout 2015 for Delhi, with October to February being the severely polluted months when the PM10 concentrations touched 500 g/m3.

Greenpeace's report holds that India's air pollution has become a "public health and economic crisis."

"India's pollution trends have been steadily increasing, with India overtaking China in number of deaths due to outdoor air pollution in 2015. India' s deteriorating air quality demands an urgent robust monitoring system," the report says.

Greenpeace explains that the country's pollution reduction strategies needs to be much more "ambitious, systematic and with focused targets with clear timelines".

It has called for accountability and a compliance mechanism, and says fossil fuel-dependant sectors such as power and transport should be shown no leniency.