"Cities can be ranked on the basis of different criteria pollutants with different results. Five cities where higher values of air quality index have been observed for the period between November 2015 to October 2016 are Delhi, Faridabad, Varanasi, Lucknow and Jaipur," Environment Minister Anil Madhav Dave said in a written reply.

He was asked which were the top five polluted cities in the country.

Replying to another question, he said the National Air Quality Index transforms complex air quality data of various pollutants into single number, nomenclature and colour for effective communication of air quality status to people in terms which are easy to understand.

There are six AQI categories - good, satisfactory, moderately polluted, poor, very poor and severe.

"In general, AQI values observed for a period of November 2015 to October 2016 indicate poor air quality in Delhi, Faridabad, Varanasi, Lucknow, Jaipur, Kanpur, Patna and Muzzaffarpur, moderately polluted air in Agra, Jodhpur, Gurgaon, Gaya, Punem Solapur, Chandrapur and Chennai," he said.

"Satisfactory air quality was in Aurangabad, Navi Mumbai, Ahmedabad, Mumbai, Vishakhapatnam, Bengaluru, Hyderabad, Panchkula, Nagpur, Thane, Haldia, Tirupathi, Rohtak, Howrah and Nashik," the minister added.

Replying to another question, Dave said out of 56 cities monitored for PM2.5 (fine particulate matter) by Central Pollution Control Board, the data for 2015 indicates that PM2.5 levels have exceeded permissible limits in Delhi, Bangalore, Bhopal, Gwalior, Singrauli, Angul, Balasore, Rourkela, Sambalpur, Talcher, Kalinga nagar, Tuticorin, Barrackpore, Durgapur, Howrah and Kolkata.

He said the analysis of monitored parameters of SO2, NO2 and PM10 in 300 cities during 2011-2015 indicates that SO2 levels were very low in Delhi, Faridabad, Pune, Ghaziabad, Barrackporeetc and ranged between 4ug/m3 (micrograms per cubic meter air) to 31ug/m3 against the National Annual Average Standard of 50ug/m3.

The NO2 levels were within the prescribed National Ambient Air Quality Standards (NAAQS) in cities except Delhi, Pune and Barrackpore during most of the years and fluctuating trends of NO2 in the range of 13ug/m3 to 74ug/m3 were observed in five years.

The PM10 levels have shown a fluctuating trend in all cities, Dave said.

Dave had earlier said in Lok Sabha that data collected by a government agency shows that ozone levels have not exceeded the permissible levels in India and reports indicating ozone pollution deaths in the country need to be "scrutinised".