Pollutant Input

Manual Calculation

PM_2.5 (Fine Particles)

μg/m³

PM₁₀ (Coarse Particles)

μg/m³

O₃ (Ozone, 8hr avg)

ppm

NO₂ (Nitrogen Dioxide)

ppb

CO (Carbon Monoxide)

ppm

SO₂ (Sulfur Dioxide)

ppb

Enter pollutant concentrations or simulate data to view AQI analysis.

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About

The Air Quality Index (AQI) is a standardized system used by government agencies to communicate the level of air pollution to the public. It transforms complex raw data - concentrations of specific pollutants like PM_2.5 and O₃ - into a single, easy-to-understand integer.

Accuracy in AQI calculation is critical for public health. The US EPA standard uses a piecewise linear interpolation formula to map local concentrations to the AQI scale (0-500). This tool allows you to input raw sensor data (in μg/m³ or ppb) to determine the exact AQI, identify the primary pollutant, and receive specific health guidance. Unlike simple weather apps, this tool handles the full mathematical derivation, including breakpoint handling for all six major criteria pollutants.

Formulas

The AQI for a specific pollutant is calculated using the piecewise linear interpolation formula:

I p = I Hi - I Lo BP Hi - BP Lo \times (C p - BP Lo) + I Lo

Where:

I_p

The index value for pollutant p

C_p

The truncated concentration of pollutant p

BP_Hi

The concentration breakpoint that is ≥ C_p

BP_Lo

The concentration breakpoint that is ≤ C_p

I_Hi

The AQI value corresponding to BP_Hi

I_Lo

The AQI value corresponding to BP_Lo

Reference Data

AQI Range	Category	Color Code	PM2.5 Breakpoints (μg/m³)	Health Implication
0 - 50	Good	Green	0.0 - 12.0	Air quality is satisfactory; little to no risk.
51 - 100	Moderate	Yellow	12.1 - 35.4	Acceptable quality; moderate concern for very sensitive groups.
101 - 150	Unhealthy for Sensitive Groups	Orange	35.5 - 55.4	Members of sensitive groups may experience health effects.
151 - 200	Unhealthy	Red	55.5 - 150.4	Everyone may experience health effects; sensitive groups more serious.
201 - 300	Very Unhealthy	Purple	150.5 - 250.4	Health warnings of emergency conditions.
301 - 500	Hazardous	Maroon	250.5 - 500.4	Health alert: everyone may experience more serious health effects.

Frequently Asked Questions

AQI is not a direct concentration. It is a unitless index derived from concentration. For example, a PM2.5 concentration of 35.4 μg/m³ equals an AQI of 100, but a concentration of 55.4 μg/m³ equals an AQI of 150. The scale is non-linear to reflect health impact steps.

The overall AQI is the maximum value calculated among all monitored pollutants (PM2.5, PM10, Ozone, CO, SO2, NO2) for that specific hour. The highest individual index becomes the location's reported AQI.

This category (AQI 101-150) suggests that the general public is unlikely to be affected, but people with lung disease, older adults, and children are at a greater risk from exposure to ozone, while persons with heart and lung disease, older adults, and children are at greater risk from the presence of particles in the air.

Yes. The US EPA standards define specific units for each pollutant (e.g., Ozone in ppm/ppb, PM in μg/m³). This tool includes internal converters to normalize inputs before applying the breakpoint formulas.