Enter Carbon Monoxide Data
Formula Used
This calculator uses the standard piecewise Air Quality Index equation: I = (Ihi−Ilo)/(Chi−Clo) × (C−Clo) + Ilo. The CO concentration C is truncated to one decimal place before indexing.
If you enter mg/m³, it converts to ppm using the ideal gas relationship: ppm = (mg/m³) × (R·T·1000)/(MW·P), where T is Kelvin and P is Pascal.
MW for carbon monoxide is 28.01 g/mol.
How to Use This Calculator
- Enter the carbon monoxide concentration from your monitor.
- Select the correct unit: ppm or mg/m³.
- Choose the averaging time used by your data source.
- If using mg/m³, optionally set temperature and pressure.
- Click Calculate AQI to view results above the form.
- Use the download buttons to export CSV or PDF.
Example Data Table
| CO (ppm) | Truncated C (ppm) | Estimated AQI | Category |
|---|---|---|---|
| 2.0 | 2.0 | 23 | Good |
| 6.0 | 6.0 | 66 | Moderate |
| 11.0 | 11.0 | 126 | Unhealthy for Sensitive Groups |
| 14.0 | 14.0 | 176 | Unhealthy |
| 20.0 | 20.0 | 231 | Very Unhealthy |
Examples are for illustration and depend on rounding rules.
What CO AQI Represents
The Air Quality Index (AQI) converts carbon monoxide (CO) concentration into a 0–500 scale that is easier to compare across days and locations. CO is a colorless gas from incomplete combustion, so elevated readings often track traffic corridors, generators, heaters, and poor ventilation. Higher AQI values indicate greater short‑term health concern.
Why Averaging Time Matters
CO exposure is assessed over time because symptoms depend on dose and duration. Many monitoring systems emphasize an 8‑hour average for community reporting, while some situations also review a 1‑hour perspective for rapid changes. This calculator lets you select the averaging time and applies the corresponding breakpoint table before calculating the AQI.
Units and Conversion to ppm
Sensors may output CO in parts per million (ppm) or milligrams per cubic meter (mg/m³). When mg/m³ is provided, the tool converts to ppm using temperature and pressure, because gas density changes with conditions. At standard conditions (25 °C and 101.325 kPa), 1 ppm of CO is approximately 1.145 mg/m³.
Breakpoint Tables and Categories
AQI categories are defined by concentration “breakpoints.” For CO, the table starts at 0.0–4.4 ppm (Good) and 4.5–9.4 ppm (Moderate), then progresses through Unhealthy for Sensitive Groups (9.5–12.4), Unhealthy (12.5–15.4), Very Unhealthy (15.5–30.4), and higher hazardous ranges. These thresholds provide consistent interpretation across regions.
Linear Interpolation Formula
Once the correct breakpoint range is found, the AQI is computed by linear interpolation. The concentration is mapped between the lower and upper breakpoints and scaled to the matching AQI interval. This method preserves continuity, so small measurement changes produce proportionate AQI changes within each category band.
Rounding and Truncation Rules
To match common reporting practice, concentrations are typically truncated before indexing into breakpoints. This calculator truncates CO to 0.1 ppm (for example, 6.29 becomes 6.2) and then rounds the final AQI to the nearest whole number. Consistent rounding avoids category flips caused by insignificant sensor noise.
Interpreting Health Messages
The category label summarizes likely impacts. “Moderate” suggests sensitive people should watch for symptoms, while “Unhealthy” and above calls for reducing strenuous outdoor activity and improving indoor ventilation. People with heart disease, older adults, and children may be affected earlier, so use the message as a conservative guide.
Practical Data Quality Tips
Place monitors away from direct exhaust plumes, calibrate when recommended, and note whether the reading is indoor or outdoor. Sudden spikes can indicate a nearby source rather than regional air quality. If CO is persistently elevated indoors, prioritize safety: improve ventilation, check appliances, and follow local health guidance.
FAQs
Which CO unit should I enter?
Enter the unit your sensor reports. Choose ppm for direct readings, or mg/m³ if your device uses mass concentration. The calculator will convert mg/m³ to ppm using temperature and pressure when needed.
What averaging time should I choose?
Use the averaging time that matches your measurement or reporting requirement. An 8‑hour view is common for community air reports, while a 1‑hour view can highlight short spikes from nearby sources.
How is AQI computed from CO?
The tool finds the CO breakpoint range that contains your value, then applies linear interpolation: I = (Ihi−Ilo)/(Chi−Clo) × (C−Clo) + Ilo. The result is rounded to a whole AQI number.
Why does the calculator truncate CO to 0.1 ppm?
Many AQI workflows use truncation to reduce noise-driven category changes. Truncating to 0.1 ppm standardizes input precision so small sensor fluctuations do not create misleading jumps in the reported AQI category.
Can I use custom temperature and pressure?
Yes. Enable the advanced switch, then enter temperature and pressure to improve mg/m³ to ppm conversion. This is helpful at high elevations or unusual weather where air density differs from standard conditions.
What does “Unhealthy for Sensitive Groups” mean for CO?
It indicates increased risk for people with heart or lung disease, older adults, and children. Sensitive individuals should reduce prolonged outdoor exertion and watch for symptoms like headache, dizziness, or shortness of breath.
Is this result a medical diagnosis or regulatory report?
No. It is an informational estimate based on standard breakpoint tables and your inputs. For official reporting, follow local authority methods and validated monitor data, especially for compliance, workplace safety, or emergency decisions.