AQI vs PM2.5 vs EU/US Scales — A Translator for Humans
Convert confusing air-quality numbers, units, and scales into clear training decisions. One guide to cut through the jargon.
Quick Answer
AQI is a unitless index (0–500) that wraps multiple pollutants into one number. PM2.5 concentration (µg/m³) is a raw measurement. The US and EU use different scales — a “Good” reading on one may be “Moderate” on another. For training: AQI below 50 is ideal, 50–100 is usually fine, above 100 deserves caution.
This is general guidance, not medical advice. Consult a healthcare provider if you have respiratory or cardiovascular conditions.
What Is AQI, Exactly?
The Air Quality Index is a standardized way to communicate how polluted the air currently is. It converts raw pollutant concentrations into a single number on a 0–500 scale. The higher the number, the worse the air quality and the greater the health concern.
AQI Ranges at a Glance
- 0–50 Good: Air quality is satisfactory. No restrictions for exercise.
- 51–100 Moderate: Acceptable for most. Unusually sensitive individuals may notice effects.
- 101–150 Unhealthy for Sensitive Groups: People with asthma or heart conditions should reduce prolonged outdoor exertion.
- 151–200 Unhealthy: Everyone may start to feel effects. Move workouts indoors.
- 201–300 Very Unhealthy: Health alert. Avoid outdoor exercise entirely.
- 301–500 Hazardous: Emergency conditions. Stay indoors.
The AQI is calculated separately for each pollutant (PM2.5, PM10, ozone, NO₂, SO₂, CO). The overall AQI reported is the highest individual sub-index.
PM2.5 Concentration vs AQI: What’s the Difference?
When you see “PM2.5: 35 µg/m³”, that’s a raw concentration — how many micrograms of fine particles are in each cubic meter of air. AQI translates that concentration into a health-risk scale. The relationship is not linear: small changes at low concentrations cause larger AQI jumps than the same change at high concentrations.
PM2.5 to US AQI Reference
| PM2.5 (µg/m³) | US AQI Range | Training Guidance |
|---|---|---|
| 0–9.0 | 0–50 (Good) | All outdoor training fine |
| 9.1–35.4 | 51–100 (Moderate) | Most can train normally |
| 35.5–55.4 | 101–150 (USG) | Sensitive groups reduce duration |
| 55.5–125.4 | 151–200 (Unhealthy) | Move workouts indoors |
| 125.5+ | 201+ (Very Unhealthy) | Avoid outdoor exercise |
Many European data sources report raw µg/m³ rather than AQI. If PM2.5 is below 9, air is generally clean. Above 35, start considering alternatives.
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Try Aeriqo FreeUS Scale vs EU Scale: Why Numbers Don’t Match
The US EPA AQI (0–500) and the European CAQI / EAQI (0–100+) use different breakpoints and categories. A reading of 50 means “Good” on the US scale but maps to something different on the European scale. This causes confusion when apps or websites mix scales without labeling them.
US EPA AQI
- • Scale: 0–500, six color-coded categories
- • Based on 24-hour or 8-hour averages depending on pollutant
- • Widely used in US apps and international platforms
EU Air Quality Index (EAQI)
- • Scale: Good / Fair / Moderate / Poor / Very Poor / Extremely Poor
- • Based on hourly concentrations for most pollutants
- • Used by the European Environment Agency and many EU countries
The practical impact: if you travel between the US and Europe, or use apps that pull from different data sources, the same air might be labeled differently. Focus on the underlying PM2.5 concentration (µg/m³) when in doubt — it’s the same everywhere.
Making Training Decisions Across Scales
Rather than memorizing conversion tables, focus on simple thresholds that work regardless of which scale your app uses.
Universal Rules of Thumb
- PM2.5 below 9 µg/m³ (US AQI ≤ 50): Train freely. This is clean air.
- PM2.5 9–35 µg/m³ (US AQI 51–100): Fine for most. Consider shortening very long sessions if sensitive.
- PM2.5 35–55 µg/m³ (US AQI 101–150): Reduce intensity and duration. Sensitive individuals should go indoors.
- PM2.5 above 55 µg/m³ (US AQI 151+): Move indoors regardless of fitness level.
Aeriqo uses the US EPA AQI scale consistently, so you always get the same reference frame — whether you’re checking air quality in Berlin, San Francisco, or Tokyo.
Frequently Asked Questions
Why do different apps show different AQI for the same city?
They may use different scales (US EPA vs European CAQI), different monitoring stations, or different averaging periods. A 24-hour average will read differently from an hourly snapshot. Always check which scale an app uses.
Which scale does Aeriqo use?
Aeriqo uses the US EPA AQI scale (0–500). This is the most widely recognized international standard and makes it easy to compare conditions across cities worldwide.
Is PM2.5 the only pollutant I should care about?
PM2.5 is the most health-relevant for exercisers, but ozone can be the dominant pollutant on hot summer afternoons. The overall AQI captures all pollutants, so use it as your primary guide and check the dominant pollutant for more detail.
Can I convert EU CAQI to US AQI?
There’s no exact one-to-one conversion because the scales use different breakpoints and averaging periods. The most reliable approach is to look at the raw PM2.5 concentration in µg/m³ and apply the universal thresholds listed above.
What does ‘Unhealthy for Sensitive Groups’ mean for healthy runners?
At this level (AQI 101–150), most healthy adults can still exercise but should consider reducing duration or intensity. If you notice any unusual symptoms — tighter breathing, throat irritation, fatigue — cut the workout short.
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