Designing new automatically generated pollen calendars for the public in Switzerland

Pollen calendars are one of the most comprehensible means to inform allergy sufferers or medical professionals about the mean presence of allergenic pollen during the course of the year. They have been produced with a variety of methods and were distributed with great success since the beginning of pollen monitoring. Current technologies, longer data series and changing user demands allow to develop new calculation methods. For designing the new pollen calendars of Switzerland, the following requirements were formulated: The pollen load levels in the calendars should correspond to the levels used in pollen forecasts. A pollen load level in the calendar should show the time window in which it potentially occurs. Further requirements were an automatic generation of the calendars, a regular update and the possibility to provide calendars for single stations, regions or specific pollen species. The data analysis is based on mean daily pollen concentrations of the last 20 years of all 14 pollen-monitoring stations in Switzerland for the 15 pollen types most relevant for allergies. For each day of the year, the 90% quantile of the daily pollen concentrations is determined in a moving 9-day time window over 20 years of data. The calculated concentrations are converted afterward into a pollen load level. The new method is flexible because various parameters can be selected freely: the reference period, the size of the moving time window, the quantile value and the thresholds for pollen load levels. Adjusting these parameters, also pollen calendars for fewer than 20 years can be calculated. However, a sensitivity analysis showed that a reference period of 20 years provides much more stable pollen calendars than shorter reference periods.