10. May 2021
Long-distance transport of grass pollen

The pollen season starts earlier and lasts longer. Pollen loads increase even before local plants start to flower. This is because wind currents can carry lightweight pollen across hundreds of kilometres.

Plants bloom earlier in the year due to rising average temperatures. With more carbon dioxide (CO2) in the air, plants not only grow better but also produce more pollen. Studies have shown this development for years.


But another important factor is often overlooked: “Pollen is meant to fly”, says Annette Menzel of the Technical University of Munich. In particular, small, very lightweight pollen varieties are transported hundreds of kilometres. “Transport phenomena have to be taken into account”, says Menzel, a professor of ecoclimatology.


The team studied at seven common allergy triggers: mugwort, birch, alder, ash, grasses, hazel and pine. They retrieved data on all seven allergens from six pollen monitoring stations from a thirty-year period, from 1987 to 2017. These stations are located in six Bavarian towns: Oberjoch in Oberallgäu, Munich, Zusmarshausen near Augsburg, and the three Franconian cities of Münnerstadt, Erlangen and Bamberg.

In addition, the researchers used weather data to determine when and where in Bavaria these allergens had started to flower.

The research team then compared both data sets – the start of flowering and the pollen measurements.

For example, if birch pollen was measured at a pollen monitoring station but the trees in the area did not start to flower until ten days later, the pollen was likely to have been transported.

“We were surprised that pollen transport is a quite common phenomenon”, says Menzel. It can account for half of the pollen load in the spring. Some stations already showed an increase in birch and hazel pollen loads eleven days before flowering; for alder and ash, the increase occurred even earlier, 16 and 19 days before flowering.

This means that not only the flowering period in the vicinity but also the pollen transported through the air before this period can have an impact on people with pollen allergies.

The data from the pollen monitoring stations were provided by the German Pollen Information Service (Stiftung Deutscher Polleninformationsdienst – PID). The data on the start of flowering of plants with allergenic pollens were sourced from the German Weather Service (DWD).




Constantin Schulte Strathaus. Allergy season starts earlier each year due to climate change and pollen transport. Press release Eureka Alert dated 25 February 2021. Last retrieved on 19 March 2021


Original study

Menzel A et al. A first Pre-season pollen Transport Climatology to Bavaria, Germany. FrontAllergy, 5 February 2021.

Other sources

Albertine JM et al. Projected Carbon Dioxide to Increase Grass Pollen and Allergen Exposure Despite Higher Ozone Levels. PLoS ONE 9(11): e111712