Prime Minister Narendra Modi's Lok Sabha constituency Varanasi on Friday was the worst polluted city in the country even as the entire focus of battling toxic air quality remained fixed on Delhi and NCR.Varanasi beat Delhi and its suburbs with average Air Quality Index (AQI) of 491 at 4 p.m.In the national capital and its adjoining regions, the average air quality was 468.The Central Pollution Control Board (CPCB) monitors air quality in 48 districts across the country. On Friday, 12 areas had "severe" air quality of which six were from Uttar Pradesh.According to CPCB's data, PM2.5 or particulate matter with diameter less than 2.5 mm, the pollutant that has direct health impacts, was the major cause of air quality deterioration in Varanasi. According to the officials of Uttar Pradesh Pollution Control Board (UPPCB), the dust from construction works in Varanasi was the major cause of pollution."Varanasi has no polluting industry around, and it (pollution) is because most of its roads are dug up and drains are being constructed, so there is heavy civil construction going on. This is the reason of high bad AQI value," UPPCB's Varanasi Regional Officer Anil Kumar Singh told IANS.Pointing out that dust pollution, along with sudden dip in temperature in the entire region, was the major cause of poor air quality in Varnasi, Singh said: "Sulphur dioxide and nitrogen oxides are all under control." The UPPCB uses CPCB's monitoring stations in Varansi.Following Varanasi, other polluted cities in India under CPCB's monitoring included Ghaziabad (485), Gurugram (480), Noida (470), Delhi (468), Bhiwadi (463), Lucknow (462), Kanpur (461), Patna (428), Faridabad (428), Muzaffarpur (409) and the Taj city Agra (404).