BharatNotes What is Particulate Matter (PM2.5 / PM10)?
Particulate Matter is the term for microscopic solid particles and liquid droplets suspended in the air. It is classified by aerodynamic diameter: PM10 comprises particles of 10 micrometres or less, while PM2.5 comprises fine particles of 2.5 micrometres or less (about 30 times smaller than the width of a human hair). PM2.5 is the more dangerous fraction because it bypasses the body's natural defences, lodges deep in the lungs and can pass into the bloodstream, raising the risk of respiratory illness, heart disease, stroke and lung cancer.
Sources
PM2.5 is mostly secondary and combustion-derived — emitted by vehicles, thermal power plants, industrial boilers, brick kilns, and the burning of biomass and crop residue (stubble). PM10 includes these sources plus coarser dust from road traffic, construction and demolition, and natural wind-blown soil. In the Indo-Gangetic Plain, winter temperature inversions trap these emissions, producing the severe smog episodes seen annually in cities such as Delhi.
Standards: WHO vs India
The World Health Organisation tightened its global air quality guidelines in 2021, citing evidence of health harm even at low concentrations. India's NAAQS were notified by the CPCB on 18 November 2009 and remain considerably more lenient than the WHO values.
| Standard | PM2.5 annual | PM2.5 24-hr | PM10 annual | PM10 24-hr |
|---|---|---|---|---|
| WHO Guideline (2021) | 5 µg/m³ | 15 µg/m³ | 15 µg/m³ | 45 µg/m³ |
| India NAAQS (2009) | 40 µg/m³ | 60 µg/m³ | 60 µg/m³ | 100 µg/m³ |
(Units: micrograms per cubic metre. WHO values per WHO Global Air Quality Guidelines, 2021; India values per NAAQS notified 18-Nov-2009.)
Reporting and Policy in India
The National Air Quality Index (NAQI) was launched on 17 September 2014 by the CPCB under the MoEF&CC. It collapses up to eight pollutants — PM2.5, PM10, NO₂, SO₂, CO, O₃, NH₃ and Pb — into a single number on a 0–500 scale across six categories (Good, Satisfactory, Moderately Polluted, Poor, Very Poor, Severe), reporting the worst sub-index as the overall AQI.
The National Clean Air Programme (NCAP), launched in January 2019, targets 130 non-attainment and million-plus cities. Its goal was initially a 20–30% cut in particulate pollution; this was revised in 2022 to a 40% reduction in PM10 (or meeting the PM10 NAAQS) by 2025–26 against a 2017 baseline. A frequent critique is that NCAP's performance is assessed mainly on PM10, despite PM2.5 being the more health-damaging fraction.
UPSC Angle
Treat PM as a "hub" topic: master the size definitions, the WHO–India standards gap, the NAQI structure, and NCAP's targets and limitations. These recur across Prelims (factual) and Mains GS3 (air-pollution governance, health and economic costs). It is a foundational concept with no single direct PYQ but underpins many questions on air pollution, smog and pollution-control institutions.
