Air Quality Index Calculator Formula

Understand the math behind the air quality index calculator. Each variable explained with a worked example.

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Formulas Used

Air Quality Index (AQI)

aqi = aqi_value

Annual Exposure Dose

annual_exposure = annual_dose

vs WHO Guideline (5 ug/m3)

vs_who = pm25 / 5 * 100

Reduction to Meet WHO

reduction_needed = pm25 - 5

Variables

VariableDescriptionDefault
pm25PM2.5 Concentration(ug/m3)35
hours_outdoorsDaily Hours Outdoors(hours)2
days_exposureAnnual Exposure Days(days)250
aqi_valueDerived value= pm25 * 4.167calculated
annual_doseDerived value= pm25 * hours_outdoors * days_exposurecalculated

How It Works

How to Calculate Air Quality Index

The AQI converts pollutant concentrations into a standardized scale.

Simplified PM2.5 to AQI

AQI (approx) = PM2.5 * 4.167 (for values up to ~100 AQI)

AQI Categories

  • 0-50: Good (green)
  • 51-100: Moderate (yellow)
  • 101-150: Unhealthy for sensitive groups (orange)
  • 151-200: Unhealthy (red)
  • 201-300: Very unhealthy (purple)
  • 301+: Hazardous (maroon)

    • The WHO guideline for annual PM2.5 is 5 ug/m3.

    Worked Example

    PM2.5 of 35 ug/m3, spending 2 hours outdoors daily for 250 days/year.

    pm25 = 35hours_outdoors = 2days_exposure = 250
    1. 01AQI: 35 * 4.167 = 146 (Unhealthy for sensitive groups)
    2. 02Annual exposure: 35 * 2 * 250 = 17,500 ug*hr/m3
    3. 03vs WHO: 35 / 5 * 100 = 700% above guideline
    4. 04Reduction needed: 35 - 5 = 30 ug/m3

    Ready to run the numbers?

    Open Air Quality Index Calculator