The Central Pollution Control Board released a list of pollution levels in Indian cities on Thursday. Tamil Nadu's Palkalaiperur has the cleanest air with good air quality index of 20. This is followed by Balasore (23), Aizawl (25), Ramanathapuram (25), Chikkaballapur (28), Madikeri (29), Madurai (29), Chikkamagaluru (30), Gangtok (30) and Nagaon (30).