Overview
The Indo‑Gangetic Plain (IGP) is one of the most intensively farmed regions on the planet. Recent studies show that the region’s winter haze is not mainly caused by visible smoke from stubble fires, but by invisible chemical reactions that turn gases into fine particles.
Key Developments
- In 2025, the CREA reported that secondary pollutants, especially ammonium sulphate, contributed to nearly one‑third of India’s PM2.5 burden.
- During the most polluted winter months, secondary pollutants made up about 41 % of fine particles in Delhi’s air.
- Professor Srinidhi Balasubramanian of IIT‑Bombay estimates that ammonia alone accounts for ≈25 % of national PM2.5, and when combined with nitrogen oxides and sulphur dioxide, the inorganic secondary share rises to ≈40 %, pushing the total secondary fraction to about 55 % of all fine particles.
- The National Aerosol Facility at IIT‑Kanpur has documented winter‑time spikes in SO₂, NOₓ, CO and ozone, confirming that cold temperatures and a shallow planetary boundary layer trap precursors and favour particle formation.
Important Facts
1. Ammonia is the dominant base in the region, with 80‑85 % of its emissions coming from agriculture.
2. The acids that react with ammonia are nitrogen oxides from combustion and sulphur dioxide from coal‑fired power plants, both of which are also high in the IGP.
3. Winter conditions (low temperature, low mixing height < 400 m) shift chemical equilibrium toward the particle phase, making the formation of ammonium nitrate and ammonium sulphate rapid.
Exam Relevance
The chemistry of secondary particles links several GS‑3 topics: air‑quality management, agricultural emissions, energy policy, and public health. Understanding the source‑sector split (agriculture vs. industry) is essential for answering questions on mitigation strategies, inter‑state coordination, and the impact of climate‑seasonal dynamics on pollution.
Moreover, the case illustrates how scientific research (e.g., the work of IIT‑Kanpur and IIT‑Bombay) informs policy. Aspirants should note the role of think‑tanks like CREA in translating data into actionable recommendations.
Way Forward
- Strengthen regulation of nitrogen‑based fertilizers and promote low‑emission alternatives.
- Upgrade coal‑based power plants with flue‑gas desulphurisation to cut SO₂ emissions.
- Implement real‑time monitoring networks linked to the National Aerosol Facility for early warning during winter inversions.
- Encourage inter‑sectoral coordination between agriculture, energy, and urban planning ministries to address the combined acid‑base chemistry.
Addressing the surplus of ammonia and the resulting secondary particles is crucial for improving winter air quality across the IGP and protecting the health of half a billion citizens.