air quality index calculator

What is the Air Quality Index (AQI)?

The Air Quality Index is a standardized way to describe how clean or polluted outdoor air is and what that means for your health. Instead of forcing people to interpret raw pollutant numbers, AQI converts measurements into a single scale from 0 to 500. Lower values are better. Higher values indicate greater health risk.

AQI is especially useful because different pollutants use different units and concentration ranges. PM2.5 is measured in micrograms per cubic meter, ozone and carbon monoxide are often measured in ppm, and gases like NO₂ can be reported in ppb. AQI puts all of those on one common scale so decision-making is easier.

How this air quality index calculator works

This calculator uses EPA-style breakpoint interpolation. For each pollutant, it finds the concentration range (breakpoint) your value falls into, then computes a pollutant-specific AQI sub-index using a linear formula. The overall AQI is the maximum of those sub-indices.

AQI categories and what they mean

• 0–50 (Good): Air quality is satisfactory, and air pollution poses little or no risk.
• 51–100 (Moderate): Acceptable for most people; unusually sensitive individuals should monitor symptoms.
• 101–150 (Unhealthy for Sensitive Groups): Children, older adults, and people with heart/lung disease should reduce prolonged outdoor exertion.
• 151–200 (Unhealthy): Everyone may begin to experience health effects; sensitive groups may experience more serious effects.
• 201–300 (Very Unhealthy): Health alert level; risk increases for everyone.
• 301–500 (Hazardous): Emergency conditions. Avoid outdoor activity and follow local public health guidance.

Pollutants included in this calculator

PM2.5 and PM10

Fine particles (PM2.5) are especially important because they can penetrate deep into the lungs and enter the bloodstream. PM10 includes larger particles that still affect breathing and inflammation.

Ozone (O₃)

Ground-level ozone is a strong respiratory irritant. It tends to be worse in sunny conditions and can trigger asthma symptoms, chest discomfort, and reduced lung function.

Carbon Monoxide (CO), Sulfur Dioxide (SO₂), and Nitrogen Dioxide (NO₂)

These gases can contribute to respiratory irritation and broader cardiovascular stress, especially in vulnerable populations. Even when levels are below emergency thresholds, sustained exposure may still matter for comfort and performance.

How to use AQI in daily life

• Check AQI before runs, bike rides, or outdoor sports.
• Shift intense workouts to earlier hours when pollution is lower.
• Use HEPA filtration indoors during high AQI events.
• Keep windows closed when AQI is in the unhealthy range.
• Wear a properly fitted respirator (such as N95) when smoke or particulate levels are high.

Important notes and limitations

AQI is a practical communication tool, not a diagnosis. Real risk depends on age, existing medical conditions, exposure duration, and pollutant mixtures. This page is intended for education and planning, not emergency medical decision-making.

Also remember that sensor quality varies. A calibrated regulatory monitor is generally more reliable than an inexpensive consumer sensor. If your local agency publishes official AQI, use that as your primary reference.

Quick FAQ

Is a single AQI number enough?

It is useful for fast decisions, but looking at the dominant pollutant gives better context.

Why does this calculator use the highest sub-index?

Because the pollutant with the highest relative health risk should drive the public health message.

Can indoor air have a different AQI than outdoor air?

Absolutely. Indoor filtration, cooking, smoking, and ventilation patterns can produce very different conditions.