Pollen, fungal spore and fluorescent particle concentrations during long-range transport events at the Sonnblick Observatory (3106m asl)

The recent rise of automatic and online instrumentation for bioaerosol research has stirred the interest from diverse scientific communities and more and more monitoring stations are installed worldwide. Providing a higher time resolution, the automatic instruments promise novel insights into atmospheric processes and distribution patterns of bioaerosols. While most stations are situated well within the atmospheric boundary layer and in populated areas, we will present data from a high alpine research station, the Sonnblick Observatory, located at 3106 m asl. Such measurements at high altitudes, far away from local sources and in atmospheric regions where clouds form, are rare.

From April 2023, a SwisensPoleno Jupiter was installed at the Sonnblick Observatory alongside a manual Hirst-type pollen trap. The SwisensPoleno Jupiter is an online aerosol monitor that obtains scattered light, two holographic images and fluorescence signals of single aerosol particles. With the Hirst-type pollen trap, the particles are collected on a sticky tape and are later examined manually under a microscope, identifying pollen and fungal spores by visual inspection. For pollen, 30 percent of the tape surface and for fungal spores 10 percent is analyzed, which exceeds the requirements of the current European standard for pollen monitoring. The increased detection area for pollen takes in account the lower concentrations which are expected at high altitudes.

In a first step, time series of concentrations and fractions of fluorescent particles (as a proxy for bioaerosols) obtained from the SwisensPoleno Jupiter were analyzed to identify particularly interesting time periods and seasonal patterns. The time series of fluorescent particles show a clear increase in the concentrations and fractions of fluorescent particles over the course of the season from early spring to summer (fluorescent fraction: 0.2 in April; 0.6 in June).

In a second step, we focused on selected time periods where FLEXPART simulations indicate long-range transport of air masses such as from the Saharan region. For these periods, we took a closer look at the fluorescence properties of the particles together with the holographic images. In a previous laboratory study, we obtained representative fluorescence signals for three classes of bioaerosol particles: pollen, fungal spores and plant debris. We use these data in combination with pollen and spore counts from the Hirst-type trap to characterize the selected events and compare them with periods with stagnant conditions and stronger local influence.