The Air quality source on the exposure indicator summarises four pollutants into a single AQI (Air Quality Index) reading. This tutorial explains which thresholds flip the verdict and where the numbers come from.
The thresholds ClearSpot uses
ClearSpot follows the European Environment Agency (EEA) AQI convention: a single 1-6 score computed from five ground-level pollutants - PM2.5, PM10, NO2, ozone (O3) and SO2.
- AQI 1-2 (Good / Fair) - verdict "Clear".
- AQI 3 (Moderate) - "Not clear" if you opted into air sensitivity. Sensitive groups may see effects.
- AQI 4-6 (Poor / Very poor / Extremely poor) - always "Not clear". General population may experience symptoms.
Behind the AQI we watch each pollutant individually against the WHO 2021 short-term guidelines. When any of these breaches its reference value the composite AQI class jumps.
What each indicator means
PM2.5 - fine particulates (WHO 24 h: 15 µg/m³)
Particles smaller than 2.5 microns - combustion soot, tyre wear, industrial aerosols. Small enough to reach the alveoli and enter the bloodstream. Linked to cardiovascular disease, stroke, lung cancer and adverse birth outcomes. The single most impactful air-quality metric in WHO's 2021 update.
PM10 - coarse particulates (WHO 24 h: 45 µg/m³)
Particles up to 10 microns - desert dust, pollen, construction sites, road dust. Irritates the upper airways and aggravates asthma. Often correlates with PM2.5 but can spike independently during dust storms or roadworks.
NO2 - nitrogen dioxide (WHO 24 h: 25 µg/m³)
Primarily a traffic pollutant, emitted by diesel engines and thermal power plants. Causes airway inflammation, reduced lung function in children, and contributes to ozone formation. High near motorways, urban canyons and ports.
O3 - ground-level ozone (WHO 8 h peak: 100 µg/m³)
Not emitted directly - produced when NOx and VOCs react in sunlight. Peaks in summer afternoons, especially downwind of cities. Strong respiratory irritant; triggers asthma attacks and can reduce exercise capacity even in healthy adults.
SO2 - sulfur dioxide (WHO 24 h: 40 µg/m³)
Mostly emitted by coal-fired power stations, heavy shipping and volcanic activity. Causes bronchoconstriction in asthmatics at low concentrations. Much less common in Europe today than a decade ago, but still relevant near ports and heavy industry.
Why the WHO 2021 values and not the EU 2008 values
The EU 2008 directive allows PM2.5 up to 25 ug/m^3 annually - a level the WHO 2021 update now describes as "harmful" on the basis of a decade of cohort studies. We default to the WHO limits because they track the most recent epidemiology, but you can switch ClearSpot back to the EU regulatory values from the cog menu if you prefer to align with local law.
What the verdict means
A "Not clear" verdict indicates that the closest CAMS forecast cell to your point has crossed the AQI 3 boundary for at least one pollutant. For sensitive groups (asthma, cardio-vascular patients, pregnant people, children) it is a reliable cue to check whether to limit outdoor exercise. For the general population it is a heads-up, not a contra-indication.
How the "composite" European AQI is built
The AQI is not a raw µg/m³ value: the EEA algorithm maps each pollutant to a sub-index, then the worst sub-index (after capping) drives the 1-6 class you see. ClearSpot reuses the same philosophy for the chip: the band threshold (60 by default) and the per-pollutant 0-5 sub-levels (from WHO 2021 24-48h targets) act as parallel tripwires so that neither a smog of NO2 only nor a dust spike of PM10 only evades the verdict.
Your thresholds vs official baselines
The WHO 2021 guideline values in the sub-index are a scientific backbone used worldwide; the EEA AQI is the regulatory bridge inside the EU. ClearSpot defaults to band 60 as the AQI "soft" line because it sits at the first tier where the general population is meant to notice outdoor air, but you can set a stricter 40 (Fair) or relax to 100 if you are comfortable using the map as a loose indicator only.
Example: the modal with pollutant rows
Expand the exposure panel and tap Air quality. The list typically shows the worst cell's AQI plus individual pollutant chips, each on the same 0-5 scale as the public air legend. If ozone sits in level 4 but PM2.5 is only level 1, a sensitive asthmatic might care about ozone first - the panel lets you cross-check the numbers before you trust a single green PM column.
Data latency and smog seasonality
Ozone and NOx couples peak on hot weekdays; particulates and wood smoke often spike on winter evenings. Model cells update on a rolling ingest - check the "period" line in the popup for the exact model month, because wildfire or Saharan intrusions can align poorly with calendar month boundaries.
Data source
ClearSpot aggregates two upstream providers:
- The Copernicus Atmosphere Monitoring Service (CAMS) 0.1-degree European forecast, updated four times a day, for PM2.5, PM10, NO2, ozone and SO2.
- Official ground stations reported via EEA when your point is within 25 km of a monitoring site, which takes precedence over the model output.
We resample to an H3 hex grid at resolution 4 and cache the result for one hour. Ground-station readings carry an "observed" tag in the indicator details.