Air quality standards and monitoring

National Ambient Air Quality Standards (NAAQS)

Ambient air is the outdoor air we breathe. The Central Pollution Control Board (CPCB) notified revised NAAQS in November 2009, covering 12 pollutants: PM10, PM2.5, SO₂, NO₂, O₃, CO, ammonia (NH₃), lead (Pb), benzene, benzo(a)pyrene, arsenic and nickel.

Key limits (for residential and industrial areas):

• PM10: 100 µg/m³ (24-hour average); 60 µg/m³ (annual).
• PM2.5: 60 µg/m³ (24-hour average); 40 µg/m³ (annual).

PM10 particles are 10 micrometres or smaller; PM2.5 are 2.5 µm or smaller, small enough to go deep into the lungs and even the bloodstream, so they are the most harmful.

Air Quality Index (AQI)

India’s National AQI turns pollutant readings into a single number and colour. It uses eight pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃ and Pb. The overall AQI is set by the worst pollutant. Categories:

• 0–50 Good; 51–100 Satisfactory; 101–200 Moderately polluted; 201–300 Poor; 301–400 Very poor; 401–500 Severe.

Monitoring

• National Air Quality Monitoring Programme (NAMP): run by the CPCB with state boards across many cities; it regularly measures SO₂, NO₂, PM10 and PM2.5.
• Manual sampling: air is pulled through a filter by a high-volume or respirable dust sampler; the filter is weighed before and after (gravimetric method) to find particulate mass. Gases are bubbled through absorbing solutions and analysed.
• Continuous Ambient Air Quality Monitoring Stations (CAAQMS) give real-time automatic data.

Role of pollution control boards

The CPCB (central) and State Pollution Control Boards (SPCBs) set standards, monitor air and water, grant “consent to establish” and “consent to operate” to industries, inspect, and take action against polluters. The National Clean Air Programme (NCAP) was launched in January 2019 to cut particulate pollution in many cities.

Key points

• NAAQS 2009: 12 pollutants.
• PM2.5: 60 (24 h), 40 (annual) µg/m³; PM10: 100 (24 h), 60 (annual) µg/m³.
• AQI: 8 pollutants; worst pollutant decides the index; 401–500 = Severe.
• NAMP is run by the CPCB.

Exam tips

Learn AQI bands in order. Questions often give an AQI value and ask for the category, or ask why PM2.5 is more harmful than PM10.

Common mistakes

• Averaging all pollutants to get AQI; the highest sub-index decides it.
• Swapping PM10 and PM2.5 limits.
• Thinking SPCBs only advise; they can grant or refuse consent.