Air Quality Index — Definition
Definition
The Air Quality Index (AQI) is a numerical scale that translates complex air pollution data into simple, color-coded information that everyone can understand. Think of it as a weather forecast for air pollution - just as we check if it's going to rain, we can check how clean or polluted the air is on any given day.
In India, the AQI ranges from 0 to 500, with lower numbers indicating cleaner air and higher numbers indicating more dangerous pollution levels. The index is divided into six categories: Good (0-50, green), Satisfactory (51-100, light green), Moderately Polluted (101-200, yellow), Poor (201-300, orange), Very Poor (301-400, red), and Severe (401-500, maroon).
Each category comes with specific health advisories - for instance, when AQI is in the 'Good' category, everyone can enjoy outdoor activities, but when it reaches 'Severe' levels, even healthy people should avoid outdoor activities and those with respiratory conditions should stay indoors.
The AQI is calculated by measuring eight different pollutants in the air: PM10 (particles smaller than 10 micrometers), PM2.5 (particles smaller than 2.5 micrometers), nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), ammonia (NH3), and lead (Pb).
Among these, PM2.5 and PM10 are often the most concerning in Indian cities because they can penetrate deep into our lungs and bloodstream. The Central Pollution Control Board (CPCB) operates a network of monitoring stations across India that measure these pollutants continuously, 24 hours a day.
The data is then processed using a complex mathematical formula to arrive at a single AQI number. What makes this system particularly important for India is that it helps citizens make informed decisions about their daily activities.
For example, if the AQI shows 'Very Poor' levels, parents might decide to keep children indoors, or people with asthma might choose to wear masks when going outside. The government also uses AQI data to implement emergency measures like the Graded Response Action Plan (GRAP) in Delhi-NCR, which can include restrictions on construction activities, vehicle movement, and industrial operations when pollution reaches dangerous levels.
From a UPSC perspective, understanding AQI is crucial because it connects environmental science with public policy, health impacts, and governance mechanisms. Questions often test not just the technical aspects of how AQI is calculated, but also its policy implications, international comparisons, and effectiveness in pollution control.
The topic frequently appears in both Prelims and Mains, often linked with current affairs about pollution crises in major cities, policy interventions like odd-even schemes, or international commitments on air quality standards.