The Pollen Season is in Full Swing – Insights from instructor in microbiology Susanne Fröjdendal Skip to main content


08 July 2024

The Pollen Season is in Full Swing – Insights from instructor in microbiology Susanne Fröjdendal

The pollen season is in full swing in Europe, and many allergy sufferers feel its effects. In Eskilstuna, Sweden the situation is closely monitored by a unique pollen trap located on the roof of the local hospital. This device provides a detailed picture of the current pollen levels, helping residents prepare for what lies ahead.

At Unilabs' microbiology lab located in Mälarsjukhuset, Eskilstuna, Susanne Fröjdendal instructor in microbiology at Unilabs oversees one of the 22 pollen stations in Sweden. The station in Mälarsjukhuset has provided critical data by measuring pollen levels from March through September. 

The process involves a pollen trap mimicking human breathing, capturing and analysing the air's pollen content. We sat down with Susanne Fröjdendal to ask a few questions about the ongoing pollen season and its impact.

What does a pollen trap look like?
The pollen trap and the drum.
This is the pollen trap, a so-called burkad trap. This device is used to monitor and measure the pollen content in the air. It operates by drawing air through a narrow slit at the front. This slit allows air to flow into the trap, carrying any pollen particles present in the environment. Behind the split there is a drum that rotates slowly and steadily. On the surface of the drum is a sticky tape and any pollen that passes inside through the gap sticks to the tape. The drum rotates at a rate of two millimetres per hour. This slow rotation allows the trap to collect a consistent sample of pollen over time.

Once the pollen data is collected using the Burkad pollen trap, we use this information to create a pollen forecast. This forecast predicts pollen levels for the coming period by considering factors such as weather and wind patterns. In addition to the current pollen levels from the trap, scientists monitor the flowering progress of various trees, grasses, and herbs. Furthermore, the flowering stages in other parts of Europe are also tracked. This is important because strong winds can carry pollen over long distances, affecting regions far from the source. For instance, this spring, strong winds from Europe brought birch pollen to northern Europe, causing problems for people with allergies.

Is it true that the pollen season now lasts from March to September for some individuals? What factors are contributing to this longer season, and how might climate change be playing a role?

The pollen season traditionally kicks off with the blooming of hazel and alder trees. The timing of their bloom depends heavily on weather and temperature conditions. Hazel trees can bloom anytime between January and April, sometimes even earlier if temperatures are favorable. Generally, hazel blooms when the temperature rises above 5 degrees Celsius. It is hard to draw any conclusions on how climate change is playing a role. It is a complex system where the temperature, the light and the weather (e.g., dryness or rainfall). For some plants, light levels are more crucial than temperature in triggering blooming.

Our pollen measurements begin in early March, making it difficult to assess if the pollen season has lengthened over time. To draw definitive conclusions, measurements would need to start much earlier in the year. However, there has been a noticeable shift in the pollen season for some spring-flowering trees, starting one to two weeks earlier over the past 40 years. But again, it is difficult to say if it is due to climate change. We can see that the amount of pollen has increased by 10-20%, which puts a higher burden on people with allergies. Some scientists attribute this increase to climate change.

Based on your measurements and data, do you foresee any significant changes in pollen patterns or levels in the coming years? How can communities better prepare for these changes?

Predicting future changes in pollen patterns is a complex task that involves multiple factors, and it's an area where climate scientists play a crucial role. While temperature is a significant factor in determining when trees and plants bloom, other elements such as light exposure, moisture levels, and overall weather conditions also influence pollen production.

For instance, last year’s dry summer led to reduced grass blooming, whereas this year saw an early surge in grass pollen due to favorable weather conditions. Additionally, as climates warm, plants that typically do not thrive in colder regions might start to survive and proliferate, potentially altering local pollen patterns.

The increasing trend of planting ornamental grasses and non-native species in Sweden can extend the pollen season. For example, ornamental grasses that bloom later in the year could prolong the period during which pollen is present in the air. Similarly, certain wind-pollinated trees like grey alder and the non-native Turkish hazel (Corylus colurna) are being planted more frequently and can contribute to early and prolonged pollen seasons.

Communities can better prepare for these changes by educating landscape architects about the allergenic potential of different plants, particularly when planning parks and public spaces. Choosing plants that are less likely to produce significant amounts of pollen can help reduce the overall pollen load in populated areas. Continuous monitoring and data collection on pollen levels can help anticipate changes and inform the public in a timely manner.

That being said: the grass pollen season is not over. We can find pollen from grass until it starts snowing.

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