The Problem With AQI: Why One Number Can’t Describe the Air You Breathe?

Air Quality Index (AQI) has become the default language of air pollution.

One number. One colour. One verdict: good or bad.

It’s simple, easy to communicate, and widely used, but it’s also deeply misleading.

While AQI plays an important role in public awareness, relying on a single number to understand air quality hides critical details about personal exposure, indoor environments, and health-relevant differences in what people actually breathe.

This article explains what AQI does well, where it falls short, and why understanding your air requires more than a single score.

What AQI Was Designed to Do?

AQI was created as a public communication tool, not a personal health diagnostic.

Its purpose is to:

• Summarise outdoor air pollution conditions

• Provide broad guidance for populations

• Trigger public health warnings during severe pollution events

AQI typically aggregates several pollutants, such as PM2.5, PM10, NO₂, O₃, SO₂, and CO, into a single worst-case value.

That simplification is intentional, but simplification always comes with trade-offs.

1. The First Problem: AQI Is Based on Averages

AQI values usually come from:

• Fixed outdoor monitoring stations

• Area-wide or city-wide averages

• Hourly or daily aggregation

This means AQI cannot tell you:

• What’s happening inside your home

• What you’re breathing in a train carriage

• How air changes room to room

• How exposure differs minute by minute

Two people in the same city, or even on the same street, can experience very different air quality, while seeing the same AQI number on their phone.

2. The Second Problem: AQI Ignores Indoor Air

Most people spend around 90% of their time indoors.

Yet AQI almost always reflects outdoor conditions only.

Indoor air quality is shaped by:

• Cooking

• Cleaning products

• Furniture off-gassing

• Poor ventilation

• Humidity and temperature changes

• Occupancy levels

Indoor pollution can be higher than outdoor pollution, even on “good AQI” days, and AQI will never show it.

3. The Third Problem: AQI Hides Pollutant-Specific Risks

AQI compresses multiple pollutants into one score.

But different pollutants affect the body in different ways.

For example:

• PM2.5 → lung and cardiovascular risk

• VOCs → headaches, irritation, long-term toxicity

• CO₂ → fatigue, reduced cognitive performance

• Humidity → mold growth, allergy triggers

• Noise → stress and sleep disruption

Two environments can share the same AQI, yet pose completely different health challenges.

A single number cannot explain why you feel unwell.

The Difference Between Air Quality and Exposure

This is the most important distinction AQI doesn’t capture.

• Air quality describes what’s in the environment

• Exposure describes what you personally experience, over time

Exposure depends on:

• Where you are

• How long you stay

• Ventilation

• Activity level

• Micro-environment conditions

A short walk on a polluted street may matter less than hours spent in a poorly ventilated indoor space, but AQI treats them equally.

Why Personal Air Data Changes the Picture?

When air is measured where you actually are, patterns emerge that AQI cannot show:

• Cooking creates short but intense PM spikes

• Meetings raise CO₂ faster than expected

• Bedrooms accumulate CO₂ overnight

• Commutes expose people to noise and particulates

• Ventilation choices immediately change conditions

This is where personal air monitoring becomes essential, not to replace AQI, but to add context and relevance.

From Public Awareness to Personal Understanding

AQI remains valuable for:

• Regional alerts

• Policy discussion

• Public health warnings

But it is not enough for:

• Daily decision-making

• Indoor health optimisation

• Understanding symptoms

• Long-term exposure awareness

Tools like PurerAir are designed to complement AQI by measuring what AQI cannot, real-time, personal, indoor and mobile exposure across multiple environmental signals.

Not one number, but a clearer picture.

Air Is Complex, Our Understanding Should Be Too

Air quality cannot be reduced to a single score without losing meaning.

If we want healthier homes, workplaces, and cities, we need to move beyond simplified indicators and toward transparent, granular, personal data.

AQI tells us there may be a problem.

Understanding your air tells you where, when, and why.