Why in the News?
A satellite-based study (2003–2020) of 141 Indian cities revealed a surprising aerosol pattern — southern cities act as pollution hotspots, while many northern cities form ‘clean islands’ due to a phenomenon called the Wind Stilling Effect.
Key Highlights of the Study:
- Conducted by: The Indian Institute of Technology Bhubaneswar.
- Method: Used high-resolution aerosol optical depth data to track pollution.
- Focus: Examined how urbanisation interacts with natural and transported pollution.
- Surprising Insight: Many northern cities were not major aerosol hotspots, contrary to assumptions.
- Classification of Cities: Two categories based on aerosol levels relative to surrounding areas:
- Urban Aerosol Pollution Islands-
- Location: Predominantly in southern and southeastern India.
- Characteristics: Cities had higher aerosol levels than nearby rural surroundings.
- Pollution Source: Mostly local emissions from vehicles, construction, and industries.
- Absence of External Influence: Minimal contribution from long-range dust or biomass burning.
- Urban Aerosol Clean Islands-
- Location: Observed in northwestern India and the Indo-Gangetic Plain.
- Pattern: Cities had lower aerosol levels than nearby upwind (southwest) areas.
- Mechanism: Incoming pollutants were blocked or deflected, creating a “clean island” effect.
- Downwind Evidence: Northeast (downwind) sides showed equal or lower aerosol levels compared to city centres.
- Urban Aerosol Pollution Islands-
About the Wind Stilling Effect:
- Overview: A phenomenon where dense urban infrastructure reduces surface wind speed, altering local airflow.
- Barrier Formation: Slowed winds create atmospheric stagnation zones, especially on the upwind side.
- Pollution Blocking: Long-range pollutants like Thar Desert dust or biomass smoke are slowed or blocked.
- Misleading Cleanliness: Cities appear cleaner not due to lower emissions, but due to pollution deflection.
- Seasonality: Most evident during the pre-monsoon season, when dust transport is high and cloud cover is minimal.
| [UPSC 2010] If there were no Himalayan ranges, what would have been the most likely geographical impact on India ?
1. Much of the country would experience the cold waves from Siberia. 2. Indo-gangetic plain would be devoid of such extensive alluvial soils. 3. The pattern of monsoon would be different from what it is at present. Which of the statements given above is/are correct ? Options: (a) 1 only (b) 1 and 3 only (c) 2 and 3 only (d) 1, 2 and 3* |
Get an IAS/IPS ranker as your 1: 1 personal mentor for UPSC 2024
