Delhi's winter smog (AQI 400+) is PM2.5 + NOx + stubble smoke — the odd-even scheme and GRAP are control attempts. The Taj Mahal's marble yellows from Mathura refinery SO₂ — the Taj Trapezium Zone bans polluting industry. CNG buses (Delhi, 2001 court order) cut CO and particulates — a policy success. Your mask on smog days filters PM2.5 — personal control.