Air quality basics
What is AQI? Air Quality Index Explained
The Air Quality Index (AQI) is a single number from 0 to 500 that shows how polluted the air is and what it means for health. India's National AQI, defined by the CPCB, is calculated from up to eight pollutants — the overall AQI equals the highest pollutant sub-index. 0–50 is Good; above 300 is Very Poor.
The Air Quality Index, commonly known as AQI, is a crucial tool for understanding the quality of the air we breathe. It provides a standardized way to measure and communicate air pollution levels, helping individuals make informed decisions about their daily activities. This article explains the full meaning of AQI, how it is calculated, the pollutants it monitors, and its significance for public health.
What is AQI?
The term "AQI" stands for Air Quality Index. It is a numerical scale used to report daily air quality, indicating how clean or polluted the air is and the associated health concerns. The AQI is designed to help people understand what local air quality means for their health. For instance, you can check the live air quality index for your city to stay updated on current conditions.
The AQI Scale Explained
The AQI scale typically ranges from 0 to 500, with higher values indicating higher levels of air pollution and greater health concerns. The scale is divided into several categories, each corresponding to a different level of health concern:
- 0-50: Good - Air quality is considered satisfactory, and air pollution poses little or no risk.
- 51-100: Moderate - Air quality is acceptable; however, some pollutants may pose a moderate health concern for a very small number of people.
- 101-150: Unhealthy for Sensitive Groups - Members of sensitive groups may experience health effects, while the general public is less likely to be affected.
- 151-200: Unhealthy - Everyone may begin to experience health effects, and members of sensitive groups may experience more serious effects.
- 201-300: Very Unhealthy - Health alert: The risk of health effects is increased for everyone, and sensitive groups should avoid outdoor activities.
- 301-500: Hazardous - Health warnings of emergency conditions. The entire population is likely to be affected.
India's National Air Quality Index (NAQI)
In India, the National Air Quality Index (NAQI) is defined by the Central Pollution Control Board (CPCB). The NAQI follows a similar structure to the international AQI but is tailored to address the specific pollutants and health concerns prevalent in India. The CPCB has established six bands to categorize air quality:
- Good: 0-50
- Satisfactory: 51-100
- Moderate: 101-200
- Poor: 201-300
- Very Poor: 301-400
- Severe: 401-500
Understanding the Pollutants
The AQI monitors a variety of pollutants, each with different health implications:
- PM2.5 and PM10: These are particulate matters, with PM2.5 being particularly concerning due to its small size and ability to penetrate deeply into the lungs. To understand why PM2.5 matters, it's important to know that it can cause respiratory and cardiovascular issues.
- NO2 (Nitrogen Dioxide): Primarily emitted from the burning of fossil fuels, NO2 can irritate the respiratory system and exacerbate asthma.
- O3 (Ozone): Ground-level ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, and other sources react chemically in the presence of sunlight. It can cause breathing problems, trigger asthma, and worsen other lung diseases.
- CO (Carbon Monoxide): A colorless, odorless gas that can be harmful when inhaled in large amounts. It reduces oxygen delivery to the body's organs and tissues.
- SO2 (Sulfur Dioxide): Emitted from the burning of fossil fuels, it can cause respiratory problems and aggravate existing heart disease.
- NH3 (Ammonia): Mainly emitted from agricultural activities, it can contribute to the formation of PM2.5 and cause respiratory issues.
- Pb (Lead): A heavy metal that can cause neurological damage, especially in children.
How to Interpret the AQI Number
Understanding the AQI number is crucial for making daily decisions about outdoor activities. For example, an AQI of 50 or below indicates good air quality, and most people can enjoy outdoor activities without any concern. However, an AQI of 100 or above may prompt sensitive groups, such as children, the elderly, and those with pre-existing health conditions, to limit their outdoor exposure. As the AQI rises, the health risks increase, and everyone may experience adverse health effects.
Why AQI Matters for Health
The AQI is more than just a number; it is a critical indicator of the potential health risks associated with air pollution. According to the World Health Organization (WHO), air pollution is a major environmental risk to health, contributing to a range of issues from respiratory infections to heart disease and lung cancer. The CPCB also emphasizes that prolonged exposure to high levels of air pollution can have serious health consequences, particularly for vulnerable populations such as children, the elderly, and those with pre-existing health conditions.
Key takeaways
- The Air Quality Index (AQI) is a standardized way to measure and communicate air pollution levels.
- India's National Air Quality Index (NAQI) is defined by the Central Pollution Control Board (CPCB) and monitors eight pollutants.
- The AQI scale ranges from 0 to 500, with higher values indicating higher levels of air pollution and greater health risks.
- Understanding the AQI number helps individuals make informed decisions about their daily activities.
- Air pollution poses significant health risks, making the AQI a vital tool for public health awareness.
By understanding the AQI and its implications, you can take proactive steps to protect your health and the health of those around you. Regularly checking the live air quality index for your city can help you stay informed and make better choices about outdoor activities.
The six AQI categories (India CPCB scale)
| AQI | Category | Associated health impact |
|---|---|---|
| 0–50 | Good | Air quality is considered satisfactory and air pollution poses little or no risk. |
| 51–100 | Satisfactory | Acceptable air quality; minor breathing discomfort possible for unusually sensitive people. |
| 101–200 | Moderate | May cause breathing discomfort to people with lung disease such as asthma, and to children and older adults. |
| 201–300 | Poor | May cause breathing discomfort to most people on prolonged exposure. |
| 301–400 | Very Poor | May cause respiratory illness on prolonged exposure; effects more pronounced for people with lung and heart disease. |
| 401–500 | Severe | Affects healthy people and seriously impacts those with existing diseases; avoid outdoor activity. |
Frequently asked questions
What is AQI in simple words?
AQI (Air Quality Index) is a single number from 0 to 500 that tells you how polluted the air is and how it affects health. The higher the number, the more polluted the air.
What is the full form of AQI?
AQI stands for Air Quality Index. In India it is officially the National Air Quality Index (NAQI), defined by the Central Pollution Control Board (CPCB).
How is the AQI calculated?
Each pollutant's concentration is converted to a sub-index using CPCB breakpoints, and the overall AQI is the highest of those sub-indices — reflecting the worst (dominant) pollutant.
Which pollutants are used in the AQI?
India's AQI uses up to eight pollutants: PM2.5, PM10, NO₂, O₃, CO, SO₂, NH₃ and lead (Pb). PM2.5 is usually the one that drives the index.
What is a good AQI?
An AQI of 0–50 is "Good" and 51–100 is "Satisfactory". Below 100 the air poses little risk to most people; above 300 it affects everyone.
Is India's AQI the same as the US AQI?
No. India uses the CPCB scale and the US uses the US EPA scale, so the same pollution can show a different AQI number. This site uses CPCB for Indian cities and US EPA for world cities.