The number shown in the risk assessment does not come from one sensor and is not produced by simply multiplying pollen by a factor. It is the result of a multi-step process combining:
- pollen by plant type;
- species-specific reference thresholds;
- weather conditions that can increase or reduce exposure;
- air quality, which can irritate the airways;
- and, if you choose, personal sensitivity to individual allergens.
This article describes pelud.net’s current calculation exactly. For Italy, the CAMS module displays six species: alder, birch, grasses, mugwort, olive and ragweed. The Italian values shown in this pilot are modeled, not locally measured, through Open-Meteo; the European model has an approximately 11 km resolution. Important local taxa such as cypress and parietaria are not among the six CAMS variables shown. The result is therefore guidance, not a diagnosis.
1. Pollen by plant type
The starting point is the estimated daily concentration in the air, expressed in grains per cubic metre (grains/m³). Italian pilot cities query the European CAMS system through Open-Meteo. The series contains alder, birch, grasses, mugwort, olive and ragweed, with hourly values converted into daily means. This is not a monitor in your neighbourhood: an approximately 11 km grid may not represent one street, park or hillside.
For each allergen we show, when available, a numerical value and a class: low, moderate, high or very high. The presence of other plants in the landscape does not mean they are included in the forecast. Cypress, parietaria/urticaceae, plane and many other families may matter locally, but they should not be interpreted as included when the page declares the six-species CAMS set.
2. Thresholds by species — DWD and EAACI
The same 8 grains/m³ do not mean the same thing for every plant. Reference thresholds derived from the German DWD index and aligned with EAACI guidance distinguish species (daily mean, grains/m³):
| Plant | Low | Moderate | High |
|---|---|---|---|
| Hazel, alder | 1–10 | 11–100 | >100 |
| Birch | 1–10 | 11–50 | >50 |
| Ash | 1–50 | 51–75 | >75 |
| Olive | 1–10 | 11–100 | >100 |
| Grasses | 1–5 | 6–30 | >30 |
| Rye | 1–2 | 3–6 | >6 |
| Ragweed, mugwort | 1–5 | 6–10 | >10 |
Allergenic potency per grain varies between plants. Ragweed and mugwort have tighter reference thresholds; the model still cannot predict an individual response. The displayed class uses that species’ threshold, not one universal scale.
3. From concentration to score — the saturation curve
Each allergen enters the calculation with a normalised value from 0 to 1. A value of 1.0 corresponds to the point where the concentration reaches that species’ high threshold.
A linear curve would make the score double whenever pollen doubled. The current calculation instead uses a concave saturation curve: it rises quickly at lower levels and flattens near 1.
score = (1 − e^(−2.5 × x)) / (1 − e^(−2.5))
Here x is the normalised value (0–1), and the result is also between 0 and 1. For grasses, with a high threshold of 31 grains/m³, 5 grains/m³ produce about 30 pollen points, 13 about 53 and 30 about 74 before weather modifiers. These are model examples, not a promise about symptoms.
4. Several allergens at once — “soft-max”
When two allergens are present together, we do not keep only the highest and do not add them fully. We use:
aggregate = highest_normalized_value + 0.5 × second_highest
The result is capped at 1.0. One allergen at 0.5 remains 0.5; two allergens at 0.5 become 0.5 + 0.25 = 0.75. The third and subsequent allergens do not enter the main aggregate. Personal sensitivity can still change the contribution of selected allergens.
5. From aggregate to pollen score
The aggregate goes through the saturation curve again and is multiplied by 75. The remaining space up to 100 lets weather and air quality modify the result.
A single reading at the DWD high threshold produces the maximum pollen score of 75 by itself. This is a model choice: a concentration already in the high band represents substantial exposure, while wind, heat or polluted air can move the overall result into a higher class.
6. Weather and air quality — the modifier
We add or subtract points for:
| Condition | Change |
|---|---|
| Wind > 25 km/h | +15 |
| Wind 15–25 km/h | +8 |
| Wind < 5 km/h | −5 |
| Humidity < 40% | +10 |
| Humidity > 75% | −8 |
| Rain > 5 mm/24h | −20 |
| Rain 1–5 mm/24h | −10 |
| Temperature ≥ 30°C | +8 |
| Temperature ≥ 25°C | +5 |
| Moderate EAQI (41–60) | +3 |
| Poor EAQI (61–80) | +6 |
| Very/extremely poor EAQI (>80) | +10 |
The combined modifier ranges from −33 to +43. Wind disperses pollen, dry air keeps it suspended and rain removes it from the atmosphere. Heat raises the modeled contribution and air quality can irritate the airways; clean air does not lower the score below its baseline. We use the European Air Quality Index obtained through Open-Meteo.
7. Personal sensitivity (optional)
In the personalisation panel each allergen can be set to:
- Normal, the default;
- Sensitive, with a doubled contribution;
- Excluded, removing it from the calculation.
Preferences are stored in your browser and apply across cities. No account is needed; on different devices you must set them again. This personalises a mathematical estimate and does not identify which allergens cause your allergy.
8. Final score — classes and outdoor time
The pollen score plus weather and air-quality modifiers is capped at 0–100:
| Points | Class | Orientative indication |
|---|---|---|
| < 30 | SAFE | No specific time limit outdoors |
| 30–49 | LOW | Up to 6 hours |
| 50–69 | MODERATE | 2–3 hours |
| 70–84 | HIGH | At most 1 hour |
| ≥ 85 | VERY HIGH | Avoid outdoor activity |
These are general indications for an average person with rhinitis. Someone with asthma or severe allergy may need more caution at every level; a non-allergic person may not have the same symptoms. The assessment is not medical advice.
Limits and sources
CAMS provides six pollen species in Europe and a modeled forecast on an approximately 11 km grid; it is not a reading at your home and does not automatically include cypress, parietaria or every Italian taxon. Thresholds and modifiers follow the structure documented by DWD, EAACI and the relevant meteorological relationships. Air quality comes from CAMS through Open-Meteo. Open-Meteo requires attribution, and the forecast remains orientative.
For individual assessment and treatment, consult your family doctor or allergist. This article is informational and is not medical advice.