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

    Frequently Asked Questions

    What is PM2.5?

    PM2.5 refers to particulate matter 2.5 micrometers or smaller. These tiny particles penetrate deep into the lungs and bloodstream, causing respiratory and cardiovascular disease. Sources include combustion, vehicles, and industry.

    What AQI level is safe for exercise?

    AQI below 50 is safe for all outdoor activities. 51-100 is acceptable for most people. Above 100, sensitive groups should limit prolonged outdoor exertion. Above 150, everyone should reduce outdoor activity.

    How can air quality be improved?

    Reducing vehicle emissions, transitioning from coal to renewables, controlling industrial pollution, reducing agricultural burning, and increasing green spaces all improve air quality.

    Ready to run the numbers?

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