Key Findings of the CREA Analysis

  • Widespread Non‑Compliance: 204 of 238 cities recorded average PM2.5 > 40 µg/m³ (Indian NAAQS) in winter 2025‑26.
  • No city met WHO safe limit of 5 µg/m³.
  • Most Polluted Cities:
  • Ghaziabad – 172 µg/m³
  • Noida – 166 µg/m³
  • Delhi – 163 µg/m³
  • Economic Hubs: Delhi (163), Kolkata (78), Mumbai (48), Chennai (44) all above NAAQS.
  • Cleanest Cities: Chamarajanagar (Karnataka) – 19 µg/m³; Bengaluru – 39 µg/m³ (just below NAAQS).
  • Regional Trend: Southern & Central/Northeastern India performed better; 8 of the 10 cleanest cities are from Karnataka.

Core Pollutants

  • PM10 & PM2.5 – particulate matter ≤10 µm and ≤2.5 µm respectively.
  • Ground‑Level Ozone (O₃) – secondary pollutant formed from NOx + VOCs under sunlight.
  • VOCs – volatile organic compounds from paints, solvents, vehicle exhaust.
  • Secondary Pollutants – e.g., photochemical smog, ground‑level ozone.

Atmospheric Phenomena

  • Photochemical Smog – brownish‑gray haze from UV‑driven reactions of hydrocarbons & NOx.
  • Temperature (Thermal) Inversion – warm air overlaying cool air traps pollutants near the surface, intensifying winter smog in northern India.
  • Acid Rain – precipitation containing nitric & sulfuric acids formed from NOx & SO₂.

Monitoring & Measurement

  • Air Quality Index (AQI) – colour‑coded index based on 8 pollutants (PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, Pb).
  • NAAQS – standards for 12 pollutants (the 8 AQI pollutants + Benzene, Benzo(a)pyrene, Arsenic, Nickel).
  • SAFAR – System of Air Quality and Weather Forecasting and Research (MoES) providing location‑specific forecasts.
  • CAAQMS – Continuous Ambient Air Quality Monitoring Stations feeding real‑time data to CPCB.

Governance & Action Frameworks

  • GRAP (Graded Response Action Plan) – tiered anti‑pollution measures for Delhi‑NCR, activated as AQI worsens.
  • Bharat Stage (BS) Emission Standards – currently BS‑VI for vehicles.
  • NCAP (National Clean Air Programme) – aims for 40 % reduction in PM2.5/PM10 by 2026 through city‑specific action plans, expanded monitoring and coordinated interventions.

Frequently Asked Questions (FAQs)

  1. What is PM2.5 and why is it dangerous?
  • Particles ≤2.5 µm penetrate deep into lungs and bloodstream, causing respiratory & cardiovascular diseases.
  1. What is the Air Quality Index (AQI)?
  • A colour‑coded tool communicating air quality based on concentrations of eight major pollutants.
  1. What is Temperature Inversion and its impact?
  • Warm air above cool air traps pollutants, leading to severe smog especially in winter.
  1. Objective of NCAP?
  • Reduce particulate matter pollution by up to 40 % by 2026 via city‑specific plans and expanded monitoring.
  1. What is GRAP?
  • Emergency framework for Delhi‑NCR implementing progressive restrictions as AQI deteriorates.

Previous Year Questions (PYQs)

  • Prelims (2025): Artificial way of causing rainfall to reduce air pollution uses (a) silver iodide and potassium iodide.
  • Prelims (2018): Difference between NGT and CPCB – NGT established by an Act; CPCB by executive order.
  • Mains (2021): Discuss revised WHO Global Air Quality Guidelines and required changes in India's NCAP.

All data are based on the CREA analysis (Winter 2025‑26) and official Indian monitoring agencies.