Why Delhi air quality deteriorates in October, Pg8

Key Highlights:

• Delhi's Air Quality Index (AQI) reached 244 on Wednesday, marking the highest level in 100 days, following Dussehra celebrations.
• Particulate matter levels, including PM10 and PM2.5, significantly exceeded permissible standards across various city locations.
• Major contributors to the pollution spike include emissions from Dussehra fireworks, post-monsoon weather changes, vehicular emissions, and farm fires.
• Vehicular emissions were the largest source, contributing an estimated 21% to PM2.5 pollution, while stubble burning contributed around 4%.
• Meteorological factors such as shallow atmospheric boundary layers and low wind speeds exacerbate the accumulation of pollutants.

Delhi AQI.jpg

Detailed Insights:

• The AQI of 244 falls into the 'poor' category, indicating potential health impacts for sensitive individuals.
• PM10 levels peaked at 488 micrograms per cubic metre in Anand Vihar, far exceeding the permissible standard of 100 micrograms per cubic metre.
• PM2.5 levels reached 305 micrograms per cubic metre in Punjabi Bagh, significantly above the permissible standard of 60 micrograms per cubic metre.
• A 2024 study by IIT Delhi researchers indicated that fireworks accounted for over 85% of measured elemental mass in PM2.5 during Diwali celebrations.
• As winter approaches, the atmospheric boundary layer becomes shallower, and night-time temperature inversions trap polluted air near the ground.
• The India Meteorological Department (IMD) states that average wind speeds below 10 kmph are unfavorable for pollutant dispersion.
• A 2026 study found that Delhi's boundary layer remained below 1 km from November to January, correlating with higher PM2.5 concentrations.
• The Indian Institute of Tropical Meteorology (IITM) Decision Support System reported stubble burning contributed 4% to Delhi's PM2.5, with a forecast to rise to 15%.
• The Indian Agricultural Research Institute (IARI) detected 1,350 farm fire events across the Northern belt between September 15 and October 21.

Scientific/Technical Concepts Involved:

• Air Quality Index (AQI): A numerical scale used to communicate daily air quality levels and associated health risks.
• Particulate Matter (PM2.5 & PM10): Microscopic solid or liquid particles suspended in the air, categorized by size, which can cause respiratory issues.
• Atmospheric Boundary Layer: The lowest part of the atmosphere directly influenced by the Earth's surface, where pollutants are mixed and dispersed.
• Temperature Inversion: A meteorological condition where a layer of warm air traps cooler air and pollutants closer to the ground.