Air Pollution and Ammonium Sulfate
Context:
A recent analysis by the Centre for Research on Energy and Clean Air (CREA) reveals that secondary aerosols like ammonium sulfate account for nearly one-third of Delhi's annual PM2.5 load
It is significantly intensifying pollution during winter smog.
Primary vs. Secondary Pollutants:
Primary Pollutants are emitted directly from sources (road dust, construction activity, open burning, vehicle exhaust, and industries)
Secondary Pollutants are formed in the atmosphere when precursor gases undergo chemical reactions influenced by humidity, temperature, and sunlight.
Ammonium sulfate is a dominant secondary inorganic aerosol.
Formation and Sources:
Ammonium sulfate forms when Sulphur Dioxide oxidizes in the atmosphere to become sulfate, which then reacts with Ammonia.
This reaction is accelerated by moist air, fog, and low winter temperatures.
Major sources of Sulphur Dioxide include coal-fired power plants, oil refineries, heavy industries, brick kilns, and diesel combustion.
Ammonia primarily arises from agricultural activities (fertilizer use, livestock waste), sewage systems, landfills, biomass burning, and diesel vehicles with catalytic converters
What are the key concerns associated with it?
Ammonium sulfate contributes around 49% of India's PM2.5 load during the post-monsoon period
These fine particles penetrate deep into the lungs
They remain airborne for days and travel long distances to affect regions far from the source.
Despite India being the world's largest emitter of SO2, the government exempted nearly 78% of coal-fired thermal power plants from installing flue gas desulphurisation (FGD) systems in July 2025.