Environment › Pollution
Air pollution
Air pollution and its control: the national programme and standards, how air quality is measured and ranked, and its sources, from vehicles and power plants to crop burning, dust and indoor fuel. Prelims has asked which gases are used to calculate the Air Quality Index and about the World Health Organization (WHO) air quality guidelines.
UPSC has asked
- Prelims 2022: the WHO Air Quality Guidelines
Showing 2 of 5 subjects, those that changed from 1 to 15 July 2026.Show all
Flue gas desulphurisation norms
Copy link to Flue gas desulphurisation normsPrelims and Mains
Flue gas desulphurisation removes sulphur dioxide from a coal plant's exhaust, usually with a limestone slurry. It was made mandatory in 2015. A 2021 notification split plants into three categories by location, and Category C, close to four fifths of the fleet, has since been exempted. Sulphur dioxide turns into sulphate particles in the air, so a distant plant adds to a city's particulate pollution.
What changed
14 Jul 2026New subject
- A study found that 20 of 37 coal plant units within 300 km of Delhi emit sulphur dioxide above the limit, and that the largest share comes from plants exempted from installing the equipment.
Mains: an airshed does not respect city limits, so a programme built city by city cannot fix a regional source.
Graded Response Action Plan
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The Graded Response Action Plan is the set of curbs on vehicles, construction and industry that the Delhi NCR applies in stages as the Air Quality Index worsens through the winter.
What changed
3 Jul 2026New subjectalso in news
- Delhi announced its winter curbs on vehicles and construction five months ahead, to run from 1 November, instead of waiting for the Air Quality Index to cross a threshold.