The Air Quality Index (AQI) Calculator converts PM2.5, PM10, ozone, NO2, SO2, and CO concentrations into the standardized EPA AQI scale from 0 to 500. Translate raw pollutant data into color-coded health categories used in public air quality alerts and environmental assessments.
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The calculator for Air Quality Index (AQI) converts measured pollutant concentrations into the standardized AQI value used by the US EPA and environmental agencies worldwide to communicate air quality risk. The AQI translates complex atmospheric chemistry data into a single intuitive number with color-coded health guidance.
The AQI runs from 0 to 500, divided into six categories:
The reported AQI is the highest value among all measured pollutants — not an average. The water quality index calculator applies similar standardized scoring to water quality parameters.
AQI is calculated using piecewise linear interpolation between breakpoints defined for each pollutant:
AQI = [(AQI_high − AQI_low) / (C_high − C_low)] × (C − C_low) + AQI_low
Different pollutants use different averaging times: PM2.5 uses 24-hour averages; ozone uses 8-hour averages; NO2 uses 1-hour averages. Using the wrong averaging period produces meaningless results. Use this online calculator with properly averaged concentration data for accurate AQI values.
Fine particulate matter (PM2.5) is the pollutant most strongly linked to adverse health outcomes. PM2.5 penetrates deep into the lungs and enters the bloodstream, causing cardiovascular and respiratory disease. Major sources include vehicle exhaust, industrial emissions, wildfire smoke, and secondary particle formation. WHO revised its PM2.5 guideline in 2021 to 5 μg/m³ annual mean — substantially stricter than the EPA's 12 μg/m³ standard, reflecting growing evidence of health effects at lower concentrations.
Ground-level ozone (O₃) forms through photochemical reactions between NOx and volatile organic compounds in sunlight. Ozone AQI is highest on hot, sunny, stagnant summer days — particularly in inland valleys. Air quality management requires understanding atmospheric chemistry beyond just emission control. The environmental science calculators cover related air, water, and ecosystem quality tools.
The AQI is calculated using linear interpolation:
AQI = ((IHi - ILo) / (BPHi - BPLo)) × (Cp - BPLo) + ILo
Where:
Categories: 0-50 Good (green), 51-100 Moderate (yellow), 101-150 Unhealthy for Sensitive Groups (orange), 151-200 Unhealthy (red), 201-300 Very Unhealthy (purple), 301-500 Hazardous (maroon).
Inputs
Results
AQI = ((100-51)/(35.4-12.1)) x (35.5-12.1) + 51 = 100.5. This PM2.5 level is just entering the Unhealthy for Sensitive Groups category.
Inputs
Results
AQI = ((50-0)/(12-0)) x (6-0) + 0 = 25. Air quality is Good, posing little or no health risk.
The AQI is a standardized index used by the EPA and agencies worldwide to communicate air pollution levels to the public. It runs from 0 to 500, with higher values indicating worse air quality and greater health concerns. The AQI is calculated separately for each pollutant, and the highest value is reported as the overall AQI.
Breakpoints are the concentration thresholds that define AQI categories. They are published in the EPA AQI Technical Assistance Document. For PM2.5 (24-hour): 0-12.0 (Good), 12.1-35.4 (Moderate), 35.5-55.4 (Unhealthy for Sensitive Groups), 55.5-150.4 (Unhealthy), 150.5-250.4 (Very Unhealthy), 250.5-500.4 (Hazardous).
In most urban areas, PM2.5 (fine particulate matter) or ground-level ozone are the pollutants that most frequently determine the AQI. PM2.5 is dominant in areas with combustion sources, construction, and wildfires. Ozone is highest in summer in areas with significant vehicle emissions and sunlight.
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