Enter pollutant concentrations
Fill any fields you have. The calculator computes each sub-index, then reports the highest AQI as the overall value.
Example data table
These examples show typical inputs and the resulting overall AQI. Your output depends on the dominant pollutant and the reporting averaging time.
| Scenario | PM2.5 (µg/m³) | PM10 (µg/m³) | O₃ 8-hr (ppb) | NO₂ (ppb) | SO₂ (ppb) | CO (ppm) | Expected AQI (approx.) |
|---|---|---|---|---|---|---|---|
| Clean morning | 7.2 | 30 | 35 | 20 | 5 | 0.8 | ~30–45 (Good) |
| Urban haze | 32.0 | 95 | 55 | 65 | 18 | 2.9 | ~90–110 (Moderate to USG) |
| Severe smoke | 180.0 | 280 | 70 | 120 | 40 | 6.2 | ~200+ (Unhealthy to Very Unhealthy) |
Formula used
The AQI is computed with linear interpolation between regulatory breakpoints for each pollutant:
I = (Ihi − Ilo) / (Chi − Clo) × (C − Clo) + Ilo
- C is the reported (and truncated) concentration.
- Clo, Chi bracket C in the pollutant table.
- Ilo, Ihi are the matching AQI breakpoints.
- The overall AQI is the maximum of all computed sub-indices.
How to use this calculator
- Collect readings from a monitor or official station report.
- Enter the concentrations you have for each pollutant.
- Choose ppb or ppm for ozone if needed.
- Click Calculate AQI to view the result panel.
- Use the table to identify the dominant pollutant.
- Download CSV or PDF to save your report.
Note: AQI depends on averaging time (8-hr, 24-hr, 1-hr). Always match your input to the stated averaging period.
Interpretation guide
Professional overview of AQI calculations
1) Why the AQI exists
The Air Quality Index converts measured pollutant concentrations into a single, comparable scale from 0 to 500. This translation helps non‑specialists interpret real-time readings and align decisions with health-based thresholds used by many agencies.
2) Pollutants commonly reported
Most networks track fine particles (PM2.5), coarse particles (PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). Each pollutant has distinct sources and physics: particles scatter and absorb light, gases participate in atmospheric chemistry.
3) Breakpoints and linear interpolation
The AQI uses concentration “breakpoints” that map ranges of C to index ranges I. Within a breakpoint band, the index is computed by linear interpolation. This calculator applies the standard equation and rounds to the nearest whole number for reporting.
4) Averaging time matters
Air quality is time‑dependent. PM values are typically based on 24‑hour averages, CO often uses an 8‑hour average, and ozone can use 8‑hour or 1‑hour periods at higher levels. Entering mismatched averaging times can shift the reported category and dominant pollutant.
5) Dominant pollutant logic
Overall AQI is defined as the maximum of all pollutant sub‑indices. A day with moderate PM2.5 but elevated ozone will be driven by ozone. This “max rule” is intentional: it highlights the worst health-relevant pollutant at that moment.
6) Typical category boundaries
Categories are aligned to AQI bands: 0–50 (Good), 51–100 (Moderate), 101–150 (Sensitive Groups), 151–200 (Unhealthy), 201–300 (Very Unhealthy), and 301–500 (Hazardous). Higher categories correspond to stronger guidance to reduce outdoor exertion.
7) Measurement quality and units
Particulate readings are reported in µg/m³, while gases are often in ppb or ppm. Small unit errors can change results by orders of magnitude. This tool supports ozone in either ppb or ppm and applies practical truncation to mimic common reporting conventions.
8) Using AQI for decisions
Use AQI trends, not only single snapshots. Rapid changes can occur during traffic peaks, temperature inversions, dust events, or wildfire smoke. For sensitive individuals, planning activities around lower‑AQI hours and improving indoor filtration can significantly reduce exposure.
FAQs
1) What does the overall AQI represent?
The overall AQI is the highest sub-index among all pollutants you entered. It indicates which pollutant creates the greatest near-term health concern and sets the category for guidance.
2) Why can ozone be entered as ppb or ppm?
Ozone is reported in different units depending on the source. This calculator converts ppb to ppm internally so it can use consistent breakpoint tables and then displays the unit you selected.
3) Why are there 8-hour and 1-hour ozone options?
Ozone standards use an 8-hour average for typical conditions, but a 1-hour value can apply when ozone is high. Enter the averaging period that matches your monitoring report.
4) Do I need to fill every pollutant field?
No. Enter any available pollutants. The tool computes sub-indices for the values provided and uses the maximum as the overall AQI.
5) Why can a small concentration change affect the category?
Breakpoints create category bands. If your value is near a breakpoint boundary, a small change can move the sub-index into the next AQI range and alter the overall category.
6) Is AQI the same everywhere in the world?
No. Some countries use different breakpoint tables or index scales. This calculator follows widely used U.S. style AQI breakpoints, which are common for educational and comparative purposes.
7) Can I use this for medical decisions?
Use it for general planning and awareness. If you have asthma or heart conditions, follow your clinician’s plan and local public health advisories, especially during high AQI events.