Lucknow is just five units behind Delhi, which has been ranked sixth, with the pollution levels of 138 micrograms per cubic metre of air.
The study titled "18-year Ambient PM2.5 Exposure and Night Light Trends in India Cities" has been published in the Aerosol and Air Quality Research, an worldwide peer reviewed journal.
According to the Union environment ministry, the data for 2017 has shown an improvement since 2016 and 2018 so far has also fared better than 2016 - indicating cleaner air due to the efforts that were made in 2017. The Government has also taken several bold initiatives, including leap-frogging from BS-IV to BS-VI.
Kanpur, a northern city on the banks of the Yamuna River, recorded an annual average PM2.5 level of 173 micrograms per cubic meter, several times higher than the World Health Organization recommendation of no more than 10 mcg per cubic meter.
Similarly, for PM 10 the figures were 289 micrograms per cubic metre in the year 2016 and 268 micrograms per cubic metre in the year 2017.
"Therefore, even PM10 levels have come down in the year 2017 against 2016", it said. But other pollution sources, including construction dust and the burning of crop stubble in the winter, continue unchecked.
"These figures from the World Health Organisation (WHO) show that as a country we still have a long way to go in the fight against air pollution, with several United Kingdom cities exceeding the air quality standards needed to protect health." he said.
Rural air pollution is carried from the big cities by wind, with lorries and other long-distance traffic also now thought to play a larger role than expected. The world's ten most polluted cities are Indian.
Significant action has been taken in Delhi and NCR, including the formulation of Graded Response Action Plan (GRAP) by CPCB.
While Delhi's air quality, according to the latest World Health Organization database for 2016, is at its worst, pollution bodies and the environment ministry say it's not a true reflection of the current reality because several measures and actions were taken in 2017, including implantation of the Graded Response Action Plan.
"This is a grim reminder that air pollution has become a national public health crisis".
It is noteworthy that nearly 1 million vehicles are added on the roads of Delhi every year and in spite of increased construction activities and vehicular movement, air quality in Delhi is showing signs of improvement.
These pollutants - some of the most risky being sulfates, nitrates and black carbon - penetrate deep into the lungs and bloodstream and cause a range of diseases including stroke, heart disease, lung cancer and other respiratory infections.