SECONDARY POLLUTANT

NEWS: A CAQM meta-analysis shows that Delhi’s winter air pollution is dominated not by direct smoke sources but by secondary particulate matter formed through chemical reactions in the atmosphere, with ammonia playing a key role

FINDINGS

Major contributors to Delhi’s winter PM2.5 pollution

• Contribution share (winter):
• Secondary particulate matter → 27% (largest)
• Transport (vehicles) → 23%
• Biomass burning → 20%
• Dust → 15%
• Industry → 9%

Primary vs Secondary particles

• Primary particulate matter: Emitted directly, Example: vehicle exhaust, smoke, dust
• Secondary particulate matter: Not emitted directly, Forms in the atmosphere through chemical reactions

Ammonia (NH₃): crucial

• CAQM highlights ammonia as the key enabler of secondary PM.
• ~80% of ammonia in India comes from agriculture

Health impact of secondary PM2.5

• 25%–60% of PM2.5 consists of sulphates & nitrates
• 5: Penetrates deep into lungs, enters bloodstream

New steps are planned

New emissions inventory & source apportionment study (base year: 2026), by:

• Automotive Research Association of India
• Indian Institute of Technology Delhi
• The Energy Resources Institute
• Indian Institute of Tropical
• Meteorology

Purpose:

• Improve Air Quality Early Warning System
• Strengthen Decision Support System (DSS)