Development and testing of a fluorescence-based UAV-mountable sensor for PBAP monitoring in the lower troposphere

Primary Biological Aerosol Particles (PBAPs) are ubiquitous in Earth’s atmosphere and have been repeatedly shown to affect human health in adverse ways as allergens or disease vectors. Their role in heterogenous freezing is also attracting increasing interest and many PBAPs are regarded as Ice Nucleating Particles (INPs) This makes PBAPs a crucial factor for Earth’s Climate. These phenomena emphasise the importance of spatially resolved information on PBAP concentrations. Current instruments use UV fluorescence spectroscopy to study PBAPs in ambient air samples, however the size and weight of these instruments limit this technique to ground- or plane-based measurements, leaving a blind spot to the lower troposphere. This highlights the need for miniaturised, UAV-mountable fluorescence spectrometers that can provide spatially resolved PBAP data from low altitudes.

To address this demand, a 3D-printed fluorescence chamber was developed and successfully tested under laboratory conditions. Due to its compact, lightweight and adaptable nature, it can be operated under UAV conditions. This was then coupled with an optical particle counter and expanded to include a wide range of different on- and offline instruments, to form a modular UAV-mountable measurement system capable of monitoring fluorescence information, particle size and mass distributions and a variety of meteorological data.

This setup was successfully used during a multi-day field campaign in Steinalpl, Styria, Austria in summer 2025. During the campaign the setup was flown consistently over an area consisting of meadows and a spruce forest suffering from heavy bark beetle infestation. The novel fluorescence spectrometer proved reliable, producing data on every flight without interruption. Preliminary results show that terrain changes can clearly be observed in the fluorescence data and that it shows correlation to other instruments from the setup, which underlines the quality of the data produced and demonstrates that the developed lightweight UAV-mountable spectrometer is an important step towards online monitoring of PBAPs in the lower troposphere.