Farm fires over, Delhi still choked: Report, Pg7

Key Highlights:

• Delhi's average PM2.5 levels in December increased by nearly 30% compared to months with stubble burning, according to a CSE analysis.
• On December 14, Delhi's AQI surged to 461, marking the season's worst air quality, even higher than during the stubble burning phase.
• Local sources within Delhi contributed about 35% of total PM2.5 in early December, with vehicles contributing nearly half of that.
• NCR cities also experienced sharp increases in PM2.5 levels in December, with Noida recording a 38% increase, Ballabhgarh 32%, Baghpat 31%, and Delhi 29%.

Detailed Insights:

• Delhi's pollution is sustained by local emissions, regional inflows, and secondary aerosol formation, with local sources accounting for 35% of PM2.5 and vehicles contributing nearly half of that.
• The remaining 65% of pollution is transported from NCR towns and beyond, highlighting the regional nature of the air quality crisis.
• Secondary particles, formed through chemical reactions of gases like NOx, SO₂, and VOCs, constitute nearly two-thirds of PM2.5, posing greater public health risks due to their toxicity and persistence.
• Transboundary pollution from vehicles, industries, power plants, waste burning, and household fuels in the NCR region are hidden drivers sustaining pollution after farm fires subside.

Key Concepts Involved:

• PM2.5: Fine particulate matter with a diameter of 2.5 micrometers or less, a major air pollutant.
• AQI (Air Quality Index): A scale used to measure and report air quality, with higher values indicating worse pollution.
• Secondary Aerosols: Pollutants formed in the atmosphere through chemical reactions of precursor gases.