Particulate matter
Also called: PM10, PM2.5 · Topic: Atmosphere: Composition, Structure and Elements of Weather · NCERT: Beyond NCERT
Meaning
Particulate matter (PM) means tiny solid or liquid bits in the air, sorted by size. PM10 particles are 10 micrometres or smaller. PM2.5 particles are 2.5 micrometres or smaller, which is tiny enough to go deep into the lungs and even into the blood. India's air-quality standards (NAAQS, 2009) set a PM2.5 annual limit of 40 µg/m³. The WHO guideline (2021) is much stricter, at 5 µg/m³. The National Clean Air Programme (2019) aims to cut PM10 by 40% by 2025-26.
Example
In winter in Delhi-NCR, smoke from stubble burning, vehicles and factories builds up. A temperature inversion (a layer of cold air trapped near the ground under warmer air) and calm winds stop the smoke from spreading out. PM2.5 levels shoot up and thick smog forms.
Don't confuse with
- Black carbon: this is one type of particle, the soot from incomplete burning. PM is the whole size-based group of particles, whatever they are made of.