How to Calculate AQI (Air Quality Index) - with Calculator - OneSDR

Air quality can have a big impact on our health and daily lives. That’s why cities and countries use the Air Quality Index (AQI) to let people know how clean — or polluted — the air is.

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In this article, we’ll walk you through what AQI means, how it’s calculated, and how you can understand it for your area.

Table of Contents

🌬️ What Is AQI?

The Air Quality Index (AQI) is a number used to communicate how polluted the air currently is or how polluted it is forecast to become. It ranges from 0 (very good) to 500 (hazardous).

The AQI takes into account multiple pollutants in the air, such as:

PM2.5 (fine particles)
PM10 (coarse particles)
Ozone (O₃)
Nitrogen dioxide (NO₂)
Carbon monoxide (CO)
Sulfur dioxide (SO₂)

Whichever pollutant has the highest index value becomes the overall AQI for that time/location.

To use the calculator select the Pollutant and its concentration.

AQI (Air Quality Index) Calculator

Select Pollutant:
Enter Concentration (µg/m³ or ppm):

AQI Result:

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📊 AQI Scale Breakdown

AQI Range	Air Quality	Health Message
0–50	Good	Air quality is satisfactory 😊
51–100	Moderate	Acceptable for most
101–150	Unhealthy for Sensitive Groups	May affect children, elderly, people with asthma
151–200	Unhealthy	Everyone may begin to feel effects
201–300	Very Unhealthy	Health alert ⚠️
301–500	Hazardous	Emergency conditions ❌

🧮 How to Calculate AQI

The AQI is calculated using a linear formula between the concentration of a pollutant and its corresponding AQI range:

AQI = [(Ihigh − Ilow) / (Chigh − Clow)] × (C − Clow) + Ilow

Where:

C = actual pollutant concentration
Clow and Chigh = the breakpoints that contain C
Ilow and Ihigh = the AQI values corresponding to Clow and Chigh

Example: PM2.5 Concentration = 55 µg/m³

From the PM2.5 AQI breakpoint table:

Clow = 35.5, Chigh = 55.4
Ilow = 101, Ihigh = 150

AQI = [(150 − 101) / (55.4 − 35.5)] × (55 − 35.5) + 101
AQI = (49 / 19.9) × 19.5 + 101
AQI ≈ 148

This means the AQI is Unhealthy for Sensitive Groups.

📍 Why AQI Matters

🫁 Alerts you to potential health risks
🏃 Helps plan outdoor activities
👨‍👩‍👧‍👦 Protects vulnerable populations
🌍 Raises awareness of pollution and environmental impact

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