Chennai, Bengaluru and Mumbai turned out to be among the best three cities in terms of having clean air during the first 40 days of the coronavirus-triggered lockdown, shows an analysis of the Central Pollution Control Board (CPCB), released on Wednesday. Chennai, Bengaluru and Mumbai turned out to be among the best three cities in terms of having clean air during the first 40 days of the coronavirus-triggered lockdown, shows an analysis of the Central Pollution Control Board (CPCB), released on Wednesday.