Delhi Air Quality Index
Delhi is consistently ranked among the world's most polluted capital cities. Annual average PM2.5 exceeds WHO guidelines by 10–20x. Winters are catastrophic — AQI regularly hits 400–600 during November smog episodes. Monsoon months (July–August) offer brief relief with AQI dropping below 100.
Delhi AQI by Month
Monthly average AQI — catastrophic in winter, briefly clean during monsoon
Delhi's Air Pollution Sources
Crop Stubble Burning
Every October–November, farmers in Punjab and Haryana burn rice stubble to quickly clear fields before wheat planting. Smoke plumes travel 300–500 km to Delhi, adding 30–50% to Delhi's PM2.5 on peak days. Despite government subsidies for alternatives, millions of acres are still burned annually.
Vehicle Emissions
Delhi has 11+ million registered vehicles — the highest of any Indian city. Diesel trucks, two-wheelers, and old buses contribute 28–40% of PM2.5. The Delhi government has implemented Odd-Even schemes and restricted old diesel vehicles, but the fleet grows by 1,500 new vehicles per day.
Diwali Firecrackers
Diwali fireworks create one of the year's worst single-night spikes. PM2.5 can reach 900+ μg/m³ (AQI 999+) on Diwali night. Delhi has banned firecrackers multiple times, but enforcement is inconsistent. The post-Diwali smog cloud can persist for 3–7 days as firework chemicals mix with agricultural smoke.
Temperature Inversions
In winter, cold dense air near the surface gets trapped under warmer air above — a temperature inversion. This atmospheric lid prevents pollutants from rising and dispersing. Combined with low wind speeds in December–January, inversions can trap pollution for 5–10 consecutive days, creating "smog episodes."
Health Protection in Delhi
Frequently Asked Questions
Why is Delhi air quality so bad?
Delhi's crisis stems from overlapping sources: 11M vehicles, industrial plants, construction dust, crop burning from Punjab/Haryana (Oct-Nov), coal power, Diwali firecrackers, and winter temperature inversions that trap all these pollutants in a bowl of stagnant air. The geography — surrounded by Aravalli hills and Punjab plains — limits natural ventilation.
Is Delhi getting better or worse?
Slowly better on some metrics. BS-VI fuel standards, expanded Metro, CNG auto-rickshaws, and coal plant closures have helped. But population growth, construction boom, and rising vehicle ownership offset gains. Annual PM2.5 averages in 2023 were still ~60 μg/m³ — 12x WHO guidelines.
What is the best time to visit Delhi?
February–March and October (early, before stubble burning) are best. July–August (monsoon) has the cleanest air but heavy rain. Avoid November–January if air quality is a concern — this is when AQI regularly hits 300–500+.
Do N95 masks actually work in Delhi?
Yes — N95 masks filter 95%+ of PM2.5 particles when worn correctly (no facial hair, snug fit). They are far more effective than surgical masks or cloth masks. N99 masks offer even better protection. Valved N95s are more comfortable for extended use but offer less protection to others.