Air Quality Management: Standards, AQI and Consent
Air Quality Management in CPCB Scientist B exams tests whether you can connect legal instruments, monitoring data and control decisions. Expect NAAQS, AQI computation, the Air Act consent system, non-attainment planning and monitoring quality.
Standards and averaging
The National Ambient Air Quality Standards (NAAQS), 2009 under the Environment (Protection) Act, 1986 cover 12 pollutants. Key 24-hour limits: PM10 100 µg/m³, PM2.5 60 µg/m³, SO2 80 µg/m³, NO2 80 µg/m³; annual PM10 60, PM2.5 40. CO is 2 mg/m³ (8 h) and 4 mg/m³ (1 h); ozone 100 µg/m³ (8 h) and 180 µg/m³ (1 h). NAAQS are ambient goals, not stack emission limits.
AQI
The CPCB AQI runs 0–500 and uses eight pollutants: PM10, PM2.5, SO2, NO2, CO, O3, NH3 and Pb. Each pollutant gets a sub-index from breakpoints; the overall AQI is the worst sub-index, not the mean. At least three pollutants, including PM2.5 or PM10, are needed. Categories: 0–50 Good, 51–100 Satisfactory, 101–200 Moderate, 201–300 Poor, 301–400 Very Poor, 401–500 Severe.
Worked example
PM2.5 24-h = 90 µg/m³. The PM2.5 breakpoint 61–90 maps to 101–200, so the sub-index is 200. PM10 24-h = 120 µg/m³; the 101–250 band maps to 101–200, giving 101 + (19/149)×99 ≈ 114. The higher value, 200, sets AQI = 200: Moderate. If you averaged 200 and 114 you would wrongly report 157.
Traps
Do not use annual limits for a 24-h AQI; do not mix µg/m³ and mg/m³; do not average sub-indices; do not call NAAQS an emission standard. Non-attainment is based on NAAQS exceedance, not AQI alone. The Air Act's Section 21 consent is separate from ambient monitoring.