Delhi winter smog
Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Beyond NCERT
Meaning
Delhi winter smog is the thick, harmful haze that covers Delhi from about November to January. The pollution comes from vehicles, dust, industry and waste burning. In winter, temperature inversion happens: cold air stays near the ground under a layer of warmer air. This acts like a lid. With calm winds and a low mixing height (the air layer in which pollution can spread is shallow), the pollution cannot escape. North-westerly winds also carry smoke from crop fires and firecrackers down the Indo-Gangetic plain into the city.
Example
In October–November, farmers in Punjab, Haryana and western Uttar Pradesh burn paddy straw to clear their fields quickly for wheat. This smoke drifts towards Delhi, and the city's AQI often reaches the Severe band. This triggers the strict stages of GRAP (Graded Response Action Plan).
Don't confuse with
- Smog in general: smog is any smoky fog over a city caused by pollution. Delhi winter smog is one seasonal case of it, made worse by inversion and crop-fire smoke.