Presets and sharing
Inputs
Advanced options
Advanced options
Calculation result
- Concentration after truncation Cp
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- Use breakpoint
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- AQI (before rounding)
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- expression
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- AQI
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- classification
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- Use breakpoint
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- Estimated concentration C_est
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- Concentration range (approximate)
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- expression
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Breakpoint (US EPA)
| Category | AQI range | Concentration range (µg/m³) |
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Note: PM2.5 is rounded down to the nearest 0.1, and PM10 is rounded down to the nearest whole number.
Assumptions, source, and limits
- This calculator follows the US EPA AQI method (40 CFR Part 58 Appendix G).
- Use 24-hour PM2.5 and PM10 averages here. Real-time metrics such as NowCast can differ.
- The calculator applies linear interpolation inside each breakpoint interval, then rounds to the nearest integer.
- Values above AQI 500 are extrapolated reference values.
- Reference: 40 CFR Part 58 Appendix G
FAQ
What is AQI?
AQI maps air pollution to a 0 to 500 scale and links each range to likely health impact.
Should I enter PM2.5 or PM10?
Choose the pollutant that matches your measured concentration. PM2.5 uses 0.1 µg/m³ truncation, while PM10 uses whole µg/m³ truncation before conversion.
Why round down and then calculate?
US EPA rules truncate PM2.5 to 0.1 units and PM10 to whole numbers before AQI conversion.
Is this the same as NowCast?
No. This page converts a concentration with the breakpoint table. Real-time public AQI may use NowCast, station quality control, or agency-specific reporting rules.
Why doesn't it match the officially announced value?
Official values may differ because of averaging windows, NowCast processing, station choice, quality control, or publisher rounding rules.
How to use the US EPA AQI calculator
Use 24-hour PM averages
This page converts measured PM2.5 or PM10 concentration in µg/m³ into the US EPA AQI category. It is intended for 24-hour average concentrations. Short-term sensor readings, NowCast values, and local agency dashboards may use a different averaging rule.
Read the breakpoint table first
AQI is not a simple linear scale from zero. The calculator finds the matching US EPA breakpoint interval, interpolates inside that interval, then rounds to the nearest integer. If a concentration is near a category boundary, a small measurement or truncation difference can change the displayed category.
Common use cases
- Convert a PM2.5 or PM10 lab/sensor value into an AQI category for a report note.
- Check which concentration range corresponds to Good, Moderate, or Unhealthy categories.
- Compare AQI conversion with related air-quality tools such as gas ppm/mg/m³ conversion or dispersion estimates.
Limits
This is a calculation helper, not an official health advisory. Official AQI can differ because of station choice, quality control, NowCast processing, local reporting rules, or pollutant combinations.