A new analysis, Air Quality Assessment of Major Indian Cities (2015–2025) by Climate Trends, finds that no major Indian city achieved safe air quality levels in the last decade. 

Key Findings of the Analysis

• Most Polluted City: Delhi recorded the worst air quality among 11 major cities analysed. Its annual mean AQI peaked above 250 in 2016 and remains unhealthy at 180 in 2025, despite improvements since 2019.
  • Northern cities like Lucknow and Varanasi began with AQI values above 200, showing improvement but still remaining above healthy limits.
• Regional Disparity: Chennai, Chandigarh, Visakhapatnam, and Mumbai saw lower AQI levels (80–140) but still above safe standards.
  • Bengaluru showed the lowest pollution levels (AQI 65–90), though still not within the safe range (AQI 0–50).

Why Northern Cities Are More Polluted

• Geography:
  • Landlocked Basin: Northern cities lie in a landlocked Indo-Gangetic Plain, bounded by the Himalayas in the north, preventing pollutant dispersion.
  • Airflow Obstruction: Due to this enclosure, pollutants cannot disperse easily and tend to stagnate over cities for long durations.
• Atmospheric Inversion During Winters
  • Winter Inversion Layer: In winter (December–February), cold, dense air near the ground gets trapped under a warm layer above, creating an atmospheric lid.
  • Reduced Vertical Mixing: Pollutants remain confined within the thin planetary boundary layer, resulting in severe choking of cities like Delhi, Lucknow, Varanasi.
• Seasonal Wind and Rain Patterns:
  • Summer & Monsoon Relief: Strong westerly winds and rainfall during monsoons help disperse pollutants across India.
  • Winter Stagnation: Lack of rain, low wind speeds, and dry air combine to intensify pollution episodes in northern cities.
• Urban Structure and Wind Resistance:
  • Surface Roughness Effect: Dense urban construction in northern megacities creates friction that slows wind speed and limits pollutant dispersion.
  • High Built-up Density: More high-rise clusters and narrow urban canyons trap particulate matter.
• Additional Regional Pollution Burden: 
  • Northern India faces heavier pollution loads due to Crop residue burning (Punjab–Haryana belt), Industrial clusters in NCR, High vehicular population, Dust from construction and mining

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Why Southern and Western Cities Fare Better

• Coastal Influence: Cities like Chennai, Mumbai, and Visakhapatnam benefit from sea breezes, which enhance dispersion.
• Higher Wind Speeds: Stronger winds prevent stagnation of pollutants.
• No Mountain Barriers: These regions lack barriers like the Himalayas, allowing freer airflow and pollutant escape.
• Monsoon Impact: The southwest monsoon brings heavy rainfall and strong westerlies that cleanse the air effectively.

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