A recent study of 141 Indian cities revealed that several northwestern and northern Indo-Gangetic Plain cities exhibit relatively lower aerosol levels than their surroundings.

• The Study was conducted by researchers of School of Earth, Ocean and Climate Sciences, IIT Bhubaneswar.
• The study is based on satellite-retrieved aerosol data from  141 cities in India from 2003 to 2020.

Key Findings of the Study

• Urban Aerosol Clean Islands (UACI): Observed in 43% of cities in northwestern and northern Indo-Gangetic Plain (IGP), where cities had lower aerosol levels than nearby areas.
• Urban Aerosol Pollution Islands (UAPI): In contrast, 57% of cities in southern and southeastern India showed higher aerosol levels within the city compared to surroundings.
• Wind Stilling Effect: Urban infrastructure weakens surface winds, forming invisible barriers that partially block aerosol entry from long-range sources like desert dust.
• Pre-Monsoon Dominance: UACI effects are most visible during the pre-monsoon period due to dry conditions and high dust transport.
• Geographical Influence: Southern cities show UAPI due to limited external pollution transport, making internal sources more dominant.
  

About Aerosols

• Aerosols are tiny solid or liquid particles suspended in the atmosphere, ranging in size from a few nanometers to tens of micrometers.
• They are mainly concentrated in the lower atmosphere (<1.5 km) due to their surface-based sources.

Types of Aerosols

Major Examples

• Mineral Dust: From deserts like the Sahara or TharSea Spray: Salt and organic matter from ocean bubbles
• Smoke: From wildfires or crop burning which is rich in black carbon
• Industrial Aerosols: Sulfates, nitrates from fossil fuel burning
• Volcanic Aerosols: Ash and sulfate from eruptions
• Biogenic Aerosols: Pollen, spores, and plant-emitted organic compounds

Positive and Negative Impacts of Aerosols

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