PM2.5 (fine particulate matter)

PM2.5 is airborne particulate matter with an aerodynamic diameter of 2.5 micrometres or less — fine particles small enough to evade the upper airways, deposit in the alveoli, and cross into the bloodstream. PM2.5 is the most health-damaging routinely-measured air pollutant: long-term exposure is causally linked to cardiovascular disease, ischemic stroke, lung cancer and reduced birth weight, with the Global Burden of Disease 2019 attributing roughly 1.67 million premature Indian deaths per year to ambient PM2.5.

India's NAAQS (2009) sets PM2.5 ambient limits at 60 µg/m³ (24-hour average) and 40 µg/m³ (annual mean), applicable uniformly across all area categories. WHO 2021 guidelines recommend 15 µg/m³ (24-hour) and 5 µg/m³ (annual) — making Indian limits 4-8x more permissive. Most North Indian cities exceed even the lenient Indian annual limit by 2-3x; Delhi annual averages run 95-110 µg/m³, Kolkata 65-75 µg/m³.

Measurement uses gravimetric samplers with WINS impactor or VSCC cyclone at the inlet to remove particles above 2.5 µm, with collection on PTFE filters. Continuous instruments rely on beta-attenuation (BAM-1020) or laser nephelometry; CPCB's 250+ CAAQMS network feeds the National Air Quality Index dashboard. PM2.5 sources split between primary emissions (combustion soot, brake dust, road resuspension) and secondary aerosols (sulphate, nitrate, ammonium formed atmospherically from SO2, NOx and ammonia).

For recycling plants, PM2.5 emissions are dominated by combustion stages — pyrolysis flue gas, tyre shredder hammer-mill operations, plastic agglomerator off-gas, biomass dryers, and in CBG plants the boilers and engines. Stack PM2.5 control requires baghouse filtration (PTFE-coated bags, 99.9%+ removal efficiency on sub-2.5 µm) or electrostatic precipitators (95-99% on fine fraction). Cyclones are useless on PM2.5 — their cut size is 5-10 µm. Wet scrubbers achieve 60-80% on PM2.5 only with venturi designs at pressure drops of 5-8 kPa, which is energy-expensive. For SPCB consent compliance, stack PM2.5 limits are typically embedded as PM (total) limits of 30-50 mg/Nm³ from which PM2.5 fraction is back-calculated by stack survey.