A new study led by researchers from Aarhus University (Denmark) shows that it is considerably more complicated for allergy sufferers to avoid grass pollen than previously thought.

Based on a three-year study with intensive measurements at three different locations in Aarhus, researchers divided the grass pollen season into three periods: a twin peak profile during the early season, a single evening profile in the middle season and a single midday profile during the late season.

Concentrations of grass pollen are influenced by many factors, the most important being the weather and the emissions, which again depends on the grass species. In Denmark alone, 230 species of grass have been recorded, of which around 20 species are likely to be particularly common in urban environments.

The emission of pollen from the individual species is driven by different weather parameters, e.g. the temperature on the previous day or on the current day, some emissions stop when it is raining, others release their pollen in response to rain. Each species flowers intensively for approximately one-two weeks, and the total season is around two months.