What is aqi

Overview

The Air Quality Index (AQI) is a standardized tool that helps people understand how clean or polluted their air is and what associated health effects they might experience. The AQI converts complex air quality data into a simple number and color-coded scale, making it accessible to the general public. The index ranges from 0 to 500, with 0 representing excellent air quality and 500 representing extremely hazardous conditions that pose serious health risks.

What Pollutants Are Measured

The AQI measures five major criteria pollutants: particulate matter (PM2.5 and PM10), ground-level ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). Each pollutant is measured separately, converted to a sub-index value on a 0-500 scale, and the highest sub-index becomes the overall AQI. This approach ensures that the overall AQI reflects the most problematic pollutant in the air at any given time.

Understanding AQI Categories

AQI values are grouped into six categories with corresponding colors. Green (0-50) indicates good air quality with minimal health concerns. Yellow (51-100) is moderate, acceptable for most but with potential concerns for sensitive groups. Orange (101-150) means unhealthy for sensitive groups—children, elderly, and those with respiratory conditions should limit outdoor activities. Red (151-200) is unhealthy for the general population. Purple (201-300) is very unhealthy with serious health effects for everyone. Maroon (301+) is hazardous, representing emergency conditions requiring everyone to avoid outdoor activity.

How AQI Is Calculated

The AQI is calculated by monitoring the concentration of each of the five criteria pollutants. Each pollutant's concentration is then converted to a sub-index using standardized formulas and breakpoints established by environmental agencies. The highest sub-index value becomes the overall AQI for that location and time. This ensures the index reflects the most problematic pollutant present, providing an accurate representation of air quality.

Global Variations

Different countries and regions use slightly different AQI systems and breakpoints. The United States uses the EPA's AQI, while China, India, and the European Union have their own variations. Despite differences in calculation methods, all major AQI systems serve the same purpose: providing accessible air quality information to help people make health decisions about outdoor activities and exposure.

Health Impacts

Air quality directly affects respiratory and cardiovascular health. Poor AQI levels can trigger asthma attacks, bronchitis, reduced lung function, and heart problems. Vulnerable populations including children, elderly people, and those with existing respiratory or heart conditions are at greatest risk. Regular AQI monitoring helps at-risk individuals take preventive measures during poor air quality days.