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Air Quality Index Calculator

Calculate the Air Quality Index (AQI) based on pollutant concentrations. Understand air quality levels and health implications for your location.

Fine particulate matter (2.5 micrometers or smaller)
Inhalable particulate matter (10 micrometers or smaller)
8-hour average ozone concentration
Annual average nitrogen dioxide concentration
1-hour average sulfur dioxide concentration
8-hour average carbon monoxide concentration

How to Use This Calculator

  1. Enter the concentration values for each pollutant
  2. Make sure to use the correct units for each pollutant
  3. Click Calculate to determine the Air Quality Index
  4. Review the AQI category and health recommendations

Formula Used

AQI = Max(I_PM2.5, I_PM10, I_O3, I_NO2, I_SO2, I_CO)
I_p = [(I_hi - I_lo)/(C_hi - C_lo)] × (C_p - C_lo) + I_lo

Where:

  • I_p = Sub-index for pollutant p
  • C_p = Concentration of pollutant p
  • C_lo, C_hi = Concentration breakpoints that encompass C_p
  • I_lo, I_hi = AQI breakpoints corresponding to C_lo and C_hi

Example Calculation

Real-World Scenario:

A city reports the following pollutant concentrations on a summer day. Let's calculate the AQI to determine air quality.

Given:

  • PM2.5 = 35.5 μg/m³
  • PM10 = 55 μg/m³
  • Ozone = 70 ppb
  • NO₂ = 30 ppb
  • SO₂ = 10 ppb
  • CO = 1.5 ppm

Calculation:

Calculate sub-index for each pollutant using the breakpoint formula:

I_PM2.5 = [(100-50)/(35.5-12.1) × (35.5-12.1) + 50 = 100

I_PM10 = [(100-50)/(54-35) × (55-35) + 50 = 55

I_O3 = [(100-50)/(70-55) × (70-55) + 50 = 100

I_NO2 = [(50-0)/(53-0) × (30-0) + 0 = 28

I_SO2 = [(50-0)/(30-0) × (10-0) + 0 = 17

I_CO = [(50-0)/(4.4-0) × (1.5-0) + 0 = 17

Result: AQI = Max(100, 55, 100, 28, 17, 17) = 100 (Moderate)

Why This Calculation Matters

Practical Applications

  • Daily health decision making
  • Urban planning and policy development
  • Environmental monitoring and alerts

Key Benefits

  • Standardized air quality communication
  • Health risk assessment
  • Informing outdoor activity decisions

Common Mistakes & Tips

Each pollutant has specific units required for accurate AQI calculation. PM2.5 and PM10 use μg/m³, while gases like O₃, NO₂, and SO₂ use ppb, and CO uses ppm. Using the wrong units will result in incorrect AQI values.

Different pollutants have different averaging time requirements for AQI calculation. For example, O₃ and CO use 8-hour averages, while SO₂ uses 1-hour averages. Make sure you're using the correct averaging period for each pollutant.

Frequently Asked Questions

PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or smaller, while PM10 includes inhalable particles with diameters of 10 micrometers or smaller. PM2.5 is more dangerous as it can penetrate deeper into the lungs and enter the bloodstream.

For general awareness, checking the AQI daily is sufficient. However, if you're in a sensitive group (children, elderly, people with respiratory conditions), or if you're planning outdoor activities, checking the AQI multiple times a day is recommended, especially during air quality alerts.

No, different countries use different AQI scales and breakpoints. The US AQI (used in this calculator) ranges from 0 to 500, while other countries like China and India have their own scales with different breakpoints and categories. Always check which AQI scale is being used when comparing values.

References & Disclaimer

Environmental Health Disclaimer

This calculator provides estimates based on the input data provided. The AQI calculation follows EPA guidelines but should not replace official air quality monitoring. For health decisions, consult with healthcare professionals and refer to local air quality reports.

References

Accuracy Notice

The accuracy of AQI calculations depends on the quality of the input data. This calculator uses the US EPA's standard AQI breakpoints and may not reflect local variations in air quality standards. For official air quality information, consult your local environmental agency.

About the Author

Kumaravel Madhavan

Web developer and data researcher creating accurate, easy-to-use calculators across health, finance, education, and construction and more. Works with subject-matter experts to ensure formulas meet trusted standards like WHO, NIH, and ISO.

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