Chennai Metro Rail, in partnership with IIT Madras, has installed smart bus shelters equipped with air purifiers, air-quality sensors, and solar roof panels. Each shelter captures PM2.5 and VOC data, displaying live air quality indices. The purification system filters particulate matter before dispersing cleaner air for waiting passengers. Trials on four routes show shelter air quality improved by 50 %, even on polluted days. The state plans to extend the system to 500 stops across Chennai and Coimbatore.