Why pollution affects north Indian cities more than south & west, Pg12

Key Highlights:

• No Indian city recorded safe air quality between 2015 and November 2025; Delhi was the most polluted.
• Cities in northern India experienced more severe pollution than those in the south and west.
• Climate Trends' analysis examined the annual mean Air Quality Index (AQI) data of 11 major cities.
• Delhi's annual mean AQI was highest in 2016 (over 250) but remained far from the safe threshold in 2025 (180).
• Bengaluru had the best air quality among the 11 cities but still did not record safe AQI levels between 2015 and November 2025.

Detailed Insights:

• The Indo-Gangetic Plain in northern India is landlocked and bordered by the Himalayas, trapping pollutants and preventing their dispersion.
• Dense urban structures in cities create surface roughness, slowing wind speeds and further limiting pollutant dispersion.
• Rain and strong westerly winds during the monsoon season help disperse pollutants, but the situation worsens in north India during winter.
• Winter inversion traps cooler air near the Earth's surface under warmer air, forming an atmospheric lid that limits vertical mixing and pollutant dispersion.
• Lucknow and Varanasi started with extremely high AQI levels but showed steady improvement after 2019, though their 2025 values remain above healthy limits.
• Chennai, Chandigarh, Visakhapatnam, and Mumbai had better air quality compared to other cities but still fell short of safe air standards.

Key Concepts Involved:

• Air Quality Index (AQI): A measure of air quality based on pollutants like particulate matter, ozone, and carbon monoxide.
• Winter Inversion: A phenomenon where cool air is trapped near the surface by a layer of warmer air above, preventing vertical mixing.
• Indo-Gangetic Plain: A large and fertile plain encompassing most of northern and eastern India, known for its high population density and agriculture.