As winter settles over Delhi, the familiar haze returns, and with it, a daily barrage of numbers on our screens. But what does an AQI of 350 actually mean for your morning walk or your child's health? Here’s a clear guide to decoding the data.
What Exactly Is the Air Quality Index (AQI)?
Think of
the AQI as a simplified report card for the air. Instead of bombarding you with complex data on multiple pollutants, it combines them into a single, colour-coded number that typically ranges from 0 to 500. The National Air Quality Index (NAQI) used in India was launched in 2014 to help the public easily understand air quality levels. It primarily tracks eight major pollutants, including PM2.5, PM10, nitrogen dioxide, and others. The final number you see is determined by the pollutant with the highest reading at that time, essentially telling you about the worst aspect of the air you are breathing.
The Pollutants That Matter Most: PM2.5 and PM10
While the AQI tracks several pollutants, the two you'll hear about most in Delhi's winter are PM10 and PM2.5. These are tiny suspended particulate matter. PM10 particles are 10 micrometres or smaller, while the far more dangerous PM2.5 particles are less than 2.5 micrometres in diameter—about 30 times smaller than a human hair. Their minuscule size allows them to bypass the body's natural defences, penetrating deep into the lungs and even entering the bloodstream. This is why PM2.5 is often called the 'real killer' and is linked to serious respiratory and cardiovascular illnesses. Sources for these particles are numerous, including vehicle exhaust, construction dust, industrial emissions, and smoke from biomass burning.
Decoding the Six Colour-Coded Categories
India's Central Pollution Control Board (CPCB) divides the AQI into six categories, each with a corresponding number range and colour to signal the level of health concern. - Good (0-50, Dark Green): The air is clean with minimal health impact. - Satisfactory (51-100, Light Green): Air quality is acceptable, though it might cause minor breathing discomfort to very sensitive people. - Moderate (101-200, Yellow): This can cause breathing discomfort for people with existing lung conditions like asthma, as well as heart disease, children, and older adults. - Poor (201-300, Orange): Most people may experience breathing discomfort on prolonged exposure. - Very Poor (301-400, Red): This level of pollution can lead to respiratory illness after prolonged exposure. The impact is more pronounced on those with existing lung and heart conditions. - Severe (401-500+, Maroon): This is a health emergency. It affects even healthy people and has serious impacts on those with existing diseases.
From Numbers to Action: What You Should Do
Knowing the numbers is one thing; acting on them is what protects your health. When the AQI enters the 'Poor' category (above 200), it's time to take precautions. For sensitive groups, even the 'Moderate' category warrants caution. - 'Moderate' (101-200): If you have asthma or heart issues, or are with children and the elderly, consider reducing prolonged or heavy exertion outdoors. - 'Poor' to 'Very Poor' (201-40) : Everyone should avoid strenuous outdoor activities like running, especially in the early morning when pollution is often trapped near the ground. Wearing a well-fitted N95 or N99 mask is crucial if you must be outside for extended periods. Surgical or cloth masks are not effective against PM2.5 particles. Consider using a HEPA air purifier in your home, particularly in the bedroom. - 'Severe' (4) : Avoid all outdoor physical activity. Keep children, the elderly, and those with chronic illnesses indoors as much as possible. Keep windows and doors closed to prevent polluted air from entering.
