Global Air Quality Indices Explained: AQI, PM Levels & WHO Guidelines

When you check the weather, you probably look for temperature and rain. But what about air quality?

Whether you’re commuting to work, exercising outdoors, or simply opening a window, air quality directly impacts your health—and yet, most people don’t fully understand what those index numbers and coloured charts really mean. This guide breaks down the world’s most common air quality indices, the pollutants they measure, and how to interpret them so you can make smarter decisions about the air you breathe.

What Is the AQI?

The Air Quality Index (AQI) is a scale used by governments around the world to report daily air pollution levels. It combines readings from multiple pollutants—like PM2.5, PM10, Ozone (O₃), Carbon Monoxide (CO), Sulfur Dioxide (SO₂), and Nitrogen Dioxide (NO₂)—into a single, easy-to-read number.

Each country may have its own variation, but most AQI systems use a 0–500 scale:

AQI Range	Description	Colour Code	Health Advisory
0–50	Good	Green	Air quality is ideal
51–100	Moderate	Yellow	Acceptable for most; sensitive groups may react
101–150	Unhealthy for Sensitive Groups	Orange	Children, elderly, MCS sufferers should limit outdoor time
151–200	Unhealthy	Red	General public may begin to experience symptoms
201–300	Very Unhealthy	Purple	Serious health risks for everyone
301+	Hazardous	Maroon	Emergency conditions – avoid all outdoor exposure

🡪 Source: US EPA AQI guidelines [1]

What’s the Difference Between AQI and PM Levels?

While AQI gives a combined risk score, you’ll often see PM2.5 and PM10 reported directly—especially on air quality monitors and apps.

PM2.5: Particles smaller than 2.5 microns—dangerous because they penetrate deep into the lungs
PM10: Larger particles like dust and pollen
PM1.0: Ultrafine particles—often found in combustion fumes and smoke (less commonly reported)

The World Health Organization (WHO) recommends the following daily exposure limits:

Pollutant	WHO 24-Hour Guideline
PM2.5	15 µg/m³
PM10	45 µg/m³
NO₂	25 µg/m³
O₃ (8-hour)	100 µg/m³

🡪 Source: WHO Global Air Quality Guidelines 2021 [2]

Most cities around the world exceed these limits regularly—especially in areas affected by traffic, industry, or seasonal wildfires.

How to Read Your Air Quality Monitor or App

When using a personal air quality monitor (like AusAir’s upcoming multi-sensor device), you’ll see real-time readings of pollutants like PM1.0, PM2.5, CO₂, and TVOCs. These are not AQI scores—but they give you raw data that can be even more powerful.

Here’s how to interpret them:

PM2.5 > 35 µg/m³ = Consider wearing a mask or using an air purifier
TVOC > 500 ppb = Open windows, ventilate space
CO₂ > 1000 ppm = Ventilation is insufficient (expect fatigue, low focus)
HCHO > 0.1 mg/m³ = Formaldehyde levels are high—consider source control or activated carbon filtration

Final Thoughts: Why It Matters

Clean air is not guaranteed, even in modern cities. With urbanisation, wildfires, and global traffic congestion, exposure to air pollution is now one of the top global health threats—linked to over 7 million premature deaths each year [3].

Understanding how to read air quality indices empowers you to take action:

Adjust your routine
Wear a high-filtration mask
Improve indoor ventilation
Use a reliable monitor to stay informed

Understanding air quality isn’t just for scientists or policymakers—it’s for anyone who breathes. Whether you're managing a health condition, looking out for your family, or simply trying to make more informed choices each day, staying aware of air quality indices can help you take meaningful steps toward a healthier life.