Calculator Form
Plotly Graph
The line below shows the PM2.5-to-AQI relationship across the current breakpoint ranges.
Example Data Table
| Example PM2.5 (µg/m³) | Truncated PM2.5 (µg/m³) | Calculated AQI | Category |
|---|---|---|---|
| 7.8 | 7.8 | 43 | Good |
| 18.6 | 18.6 | 69 | Moderate |
| 42.3 | 42.3 | 118 | Unhealthy for Sensitive Groups |
| 88.9 | 88.9 | 174 | Unhealthy |
| 180.2 | 180.2 | 255 | Very Unhealthy |
PM2.5 AQI Breakpoint Table
| Category | PM2.5 Low (µg/m³) | PM2.5 High (µg/m³) | AQI Low | AQI High |
|---|---|---|---|---|
| Good | 0.0 | 9.0 | 0 | 50 |
| Moderate | 9.1 | 35.4 | 51 | 100 |
| Unhealthy for Sensitive Groups | 35.5 | 55.4 | 101 | 150 |
| Unhealthy | 55.5 | 125.4 | 151 | 200 |
| Very Unhealthy | 125.5 | 225.4 | 201 | 300 |
| Hazardous | 225.5 | 325.4 | 301 | 500 |
Values above 500 are beyond the standard AQI scale and should be handled with Hazardous precautions.
Formula Used
I = ((Ihigh - Ilow) / (Chigh - Clow)) × (C - Clow) + Ilow
In this equation, C is the truncated PM2.5 concentration, while Clow and Chigh are the concentration breakpoints that surround the reading. Ilow and Ihigh are the AQI breakpoints for the same category band.
The workflow is:
- Read the PM2.5 concentration in µg/m³.
- Truncate the concentration to one decimal place.
- Find the matching breakpoint range.
- Interpolate using the equation above.
- Round the resulting AQI to the nearest whole number.
How to Use This Calculator
- Enter an optional reading label, location, and sample date.
- Select the source type for your record keeping.
- Leave the averaging basis as 24-hour average.
- Enter the PM2.5 concentration in µg/m³.
- Click Calculate AQI.
- Review the AQI result, category, health meaning, and action advice.
- Use the Plotly chart to see where the value sits on the curve.
- Download the result as CSV or PDF if needed.
Frequently Asked Questions
1. What does PM2.5 AQI mean?
It converts a fine-particle concentration into an easier public health scale. AQI tells how polluted the air is and what level of caution people should use outdoors.
2. Why does the calculator truncate PM2.5 to one decimal?
The AQI method uses PM2.5 values truncated to one decimal place before interpolation. That keeps calculations aligned with standard reporting practice for this pollutant.
3. Is this for hourly PM2.5 readings?
No. This version is built for the 24-hour PM2.5 AQI method. A single instant sensor reading may not represent the required average concentration.
4. Can I use low-cost sensor data here?
Yes, for screening or education. However, raw low-cost sensor values may need correction or validation before being used for formal public reporting decisions.
5. What happens when AQI goes above 100?
Once AQI exceeds 100, air quality becomes unhealthy at least for sensitive groups. As values rise, the expected health concern and recommended precautions become stronger.
6. What if the concentration produces an AQI above 500?
Values above 500 are beyond the standard AQI scale. This calculator shows 500+ and applies Hazardous guidance, which is the safest practical interpretation.
7. Is indoor AQI calculated the same way?
The math can be the same, but indoor interpretation may differ because exposure patterns, filtration, and source conditions are different from outdoor regulatory reporting.
8. How often should I recalculate AQI?
Recalculate whenever you receive a new validated 24-hour PM2.5 value. During smoke events or rapid pollution changes, updated daily values are especially useful.
Important Notes
- This calculator is designed for PM2.5 only.
- It does not combine ozone, PM10, CO, SO₂, or NO₂ into a daily overall AQI.
- For public alerts, use local official air quality services where available.
- Low-cost sensor readings may need calibration corrections before formal interpretation.