A pollen forecast estimates how much airborne pollen you may encounter over the next few days. It cannot predict whether you will have symptoms. Your response depends on the pollen you are allergic to, your sensitivity, your exposure, and your treatment.
Airpult groups six CAMS European pollen forecasts into tree, grass, and weed levels. Use those levels to judge timing and relative intensity, not as a medical threshold or a guarantee for your street.
What pollen is
Pollen grains are microscopic particles that seed plants release for reproduction. Many trees, grasses, and weeds are wind-pollinated. They produce large amounts of light pollen that can stay airborne and travel far from the plant.
Insect-pollinated flowers often produce stickier pollen that is less important as a widespread outdoor allergen. Hay fever is therefore driven mainly by a smaller set of wind-borne species, not by every plant that is in bloom.
Not all allergenic pollen behaves the same way. Birch and olive are both trees, but they flower in different regions and seasons. Grass pollen is a mixture of species. Mugwort and ragweed are both weeds, yet they are not interchangeable.
A high total can therefore hide the plant that matters to you. If you know your trigger, read the group that contains it, then remember that the group may still mix several species.
What a pollen count measures
A pollen count is the concentration of pollen grains in the air, usually reported as grains per cubic metre. A daily count commonly represents the average concentration observed over 24 hours. It describes the sample collected at one monitoring site, so it may not match conditions at every address nearby.
Traditional monitoring networks use Hirst-type volumetric traps. A pump draws air across an adhesive strip on a slowly rotating drum. Analysts divide the strip into daily samples, then identify and count pollen under a microscope. These observations are retrospective, and reporting delays vary by network.
Automated monitors used by MeteoSwiss can identify selected pollen types within minutes. Manual traps remain important for long records and a wider range of pollen.
A trap count is still a local sample. Nearby vegetation, elevation, a sheltered street, or local wind can make your exposure different from the station, and from a model grid cell.
How the forecast is made
Airpult uses the CAMS European air quality forecast. It provides hourly pollen concentrations on a grid of about 10 kilometres, updates daily, and extends four days ahead. The dataset covers alder, birch, grass, mugwort, olive, and ragweed pollen. Coverage follows that European CAMS domain, so pollen levels are shown for European locations rather than worldwide.
CAMS uses the median of 11 European forecasting systems. The models estimate when plants release pollen and how weather transports or removes it. They combine plant distribution, phenology, recent weather, and atmospheric transport. The spread between their results provides an estimate of forecast uncertainty, and CAMS evaluates pollen output against observations from European Aeroallergen Network stations.
A forecast value is still a model estimate for a grid cell, not a measurement at your exact location. CAMS also classifies pollen variables as experimental because they are not among the pollutants that receive its regular in-situ validation. Use the forecast to identify the likely level and timing, rather than treating a precise number as a guarantee.
The CAMS output has hourly steps, but it is recalculated once a day. An hourly point is therefore part of a modelled daily forecast, not a new observation made at that hour. Forecast uncertainty generally matters more further into the four-day period.
What Airpult’s levels mean
Airpult combines the six CAMS pollen forecasts into the three groups shown on a location’s forecast page:
- Tree : alder, birch, and olive concentrations added together.
- Grass : grass concentration.
- Weed : mugwort and ragweed concentrations added together.
Airpult applies the same display bands to each group, in grains per cubic metre:
- Low : 2.4 or lower.
- Moderate : above 2.4 through 4.8.
- High : above 4.8 through 7.2.
- Very high : above 7.2.
These are Airpult display bands, not universal medical symptom thresholds. People can react at different concentrations, and grouping several species can hide which plant is driving the total. A high tree value, for example, does not tell you whether alder, birch, or olive is responsible.
The pollen thresholds published by the European Academy of Allergy and Clinical Immunology define the start and end of pollen seasons and peak periods using several consecutive days. They should not be read as Airpult index cut-offs or as a guarantee that symptoms will or will not occur on one day.
A pollen forecast and the air-quality index also measure different things. A low AQI does not mean that pollen is low, or vice versa. See AQI: How the Air Quality Index Works for the pollutant scale.
When pollen seasons happen
Tree pollen often appears earlier in the year, grass pollen follows later, and weed pollen can remain important into the later part of the growing season. The order and timing vary by species, latitude, elevation, and weather. A broad group such as “tree” can also contain several species with different seasons, so the calendar is a clue rather than a fixed schedule.
Tree pollen
Alder is often among the earliest tree pollens in much of Europe. Birch is a major spring allergen in northern and central Europe. Olive is important in Mediterranean regions and can dominate the tree total there even when birch is not.
Because Airpult adds alder, birch, and olive together, a high tree level in southern Europe may have a different cause from a high tree level farther north.
Grass pollen
Grass pollen usually becomes important after the main tree season in a given climate, then can persist through late spring and summer. It is one of the most common outdoor hay-fever triggers in Europe. The CAMS grass field is a single combined forecast, not a list of individual grass species.
Weed pollen
Mugwort and ragweed typically matter later in the growing season. Ragweed pollen can travel long distances on the wind, so a high weed level is not always produced by plants immediately beside you. As with trees, a combined weed total does not say which of the two is responsible.
How weather changes pollen
Weather affects both release and transport. No single factor controls the day.
Warm, dry conditions
Warm, dry conditions can favour flowering and pollen release. These days often bring higher airborne concentrations, but plant readiness still matters. A warm day before the local season has started will not create a high forecast by itself.
Wind
Wind can carry pollen away from its source, sometimes over long distances. Dry, windy weather can raise concentrations far from the plants that produced the grains. Local shelter can also do the opposite and keep your street different from the grid value. Wind Speed Explained covers how terrain changes exposure.
Rain
Rain often removes pollen from the air, but the effect depends on its timing and intensity, the plant, and whether conditions dry out again. There is no dependable rule that every rainy day lowers exposure or that the next day always brings a spike. What Is Precipitation? explains how rain intensity and duration differ.
Humidity
Humidity also affects pollen release and particles differently across species and situations. High humidity alone does not guarantee low exposure. Humidity and Dew Point Explained shows why a percentage needs temperature context. The MeteoSwiss pollen model description shows why forecasts account for temperature, wind, precipitation, plant distribution, and recent weather together.
Thunderstorms
Thunderstorm asthma is a narrower risk than the name suggests. Some storms during periods of high grass pollen can expose people to small allergen particles and trigger sudden asthma symptoms. Events are uncommon. People with current, past, or undiagnosed asthma, and people with hay fever, face greater risk, especially when asthma is poorly controlled.
A pollen forecast alone is not a thunderstorm-asthma forecast. Follow local health warnings and your asthma action plan. Victoria’s health guidance explains the risk and precautions. Thunderstorms and Lightning: How They Form covers storm structure more generally.
Planning for high pollen
- Check the forecast before extended outdoor activity and pay attention to the pollen type that triggers you.
- On high-pollen days, limiting outdoor activity, closing windows, and showering and changing clothes after time outside can reduce exposure.
- Avoid drying laundry outdoors when levels are high if pollen on fabric bothers you.
- Follow your medication label and your clinician’s plan. The American Academy of Allergy, Asthma & Immunology advises that many seasonal-allergy medicines work best when started before exposure and symptoms, but there is no single two-to-four-week rule for every medicine.
- If you rinse your nose, use distilled or sterile water, or tap water that has been boiled and cooled. Follow the device instructions and keep it clean. The CDC’s nasal-rinsing guidance explains the safe-water requirement.
- If pollen affects your breathing or your usual treatment is not controlling symptoms, contact a healthcare professional.
Pollen is only one possible outdoor trigger. If your symptoms do not follow the pollen forecast, mould, dust, or smog may also be relevant. Beyond Pollen: Mould, Dust and Smog covers those other outdoor and indoor sources.
How Airpult shows pollen
Use Airpult’s explore page to find a city or town. For European locations, the forecast page shows the current tree, grass, and weed level alongside air-quality information. Those labels are the display bands above, derived from the grouped CAMS concentrations.
Compare the current levels with your plans, and check again when the daily forecast updates. A change after rain or a wind shift is more informative than one snapshot taken in isolation.
