Delhi’s hazardous daytime air pollution results from a combination of human activities and natural factors. The major causes include:
1. Vehicular Emissions
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High population and rapid growth in vehicle ownership.
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Traffic congestion leads to idling, increasing emissions.
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Major pollutants: PM2.5, PM10, NOx, CO, and ozone precursors.
2. Industrial and Power Plant Emissions
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Factories around Delhi-NCR emit particulate matter, sulfur dioxide (SO₂), and nitrogen oxides (NOx).
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Brick kilns and small-scale industries often use dirty fuels like coal, wood, and furnace oil.
3. Construction and Road Dust
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Continuous construction, demolition, and poor dust-control practices release large amounts of PM10.
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Road dust resuspension due to traffic movement is one of the largest daytime contributors.
4. Biomass Burning Within the City
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Burning of garbage, wood, and crop waste inside Delhi’s informal settlements contributes to toxic emissions.
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Open waste burning is a major source of black carbon.
5. Stubble Burning (Seasonal but Severe)
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Farmers in Punjab, Haryana, and Uttar Pradesh burn rice stubble.
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Winds carry the smoke to Delhi, dramatically raising PM2.5 levels, especially in late October–November.
6. Atmospheric and Weather Conditions
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Low wind speed during the day traps pollutants.
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Temperature inversions can occur even in daytime winter months, preventing vertical dispersion.
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Strong sunshine triggers photochemical reactions, increasing ground-level ozone.
7. Urban Heat Island Effect
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Dense built-up areas trap heat, intensifying chemical reactions that form secondary pollutants like ozone and secondary PM2.5.
8. Diesel Generators
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Commonly used during power cuts in markets, construction sites, and residential complexes.
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Emit high levels of PM2.5, SO₂, and NOx.
9. Poor Fuel Quality & Waste Disposal Practices
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Use of substandard fuels in transport and industry.
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Improper waste disposal leads to open burning, especially during daytime when enforcement is weak.
Summary
Delhi’s hazardous daytime air pollution arises from a mix of local emissions (vehicles, dust, industries), regional sources (crop burning), and weather conditions that trap pollutants and enhance photochemical pollution.
B S Vohra, Environment Activist, President, East Delhi RWAs Joint Front
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