Alder
Late winter, windborne tree pollen in central and northern Europe.
Understand the pollen scale
Pollen forecasts come from Open-Meteo in grains per cubic metre. ClearSpot maps those raw counts to a 0 to 5 scale so you can see at a glance whether the air in your area is risky for allergy sufferers.
The six levels
| Level | Label | Range (grains/m3) |
|---|---|---|
| 0 | None | 0 |
| 1 | Very low | 1 - 2 |
| 2 | Low | 3 - 10 |
| 3 | Moderate | 11 - 30 |
| 4 | High | 31 - 50 |
| 5 | Very high | > 50 |
Ranges above are given for grass pollen, the most common reference allergen. Tree pollens (birch, olive) tolerate higher counts before reaching the same risk level; see the technical thresholds in PollenScale.php for exact values per taxon.
Taxa covered
Birch
Early spring, one of the most allergenic tree pollens.
Grass
May to July peak, the reference allergen for hay fever.
Mugwort
Late summer herbaceous pollen, often co-reactive with ragweed.
Olive
Late spring, highly allergenic around the Mediterranean basin.
Ragweed
Late summer to autumn, severe allergen even at low counts.
Sources: Open-Meteo Air Quality API for raw grains/m3 values, RNSA / EAACI literature for the per-taxon risk bands. Thresholds are conservative and can be tuned in src/common/PollenScale.php.