Abstract
Terrestrial ecosystems can influence atmospheric processes by contributing a huge variety of biological aerosols (bioaerosols) to the environment. Several types of biological particles, such as pollen grains, fungal spores, and bacteria cells, trigger freezing processes in super-cooled cloud droplets, and as such can contribute to the hydrological cycle. Even though biogenic particles are known as the most active form of ice nucleation particles (INPs), the transport to high tropospheric altitudes, as well as the occurrence in clouds, remains understudied. Thus, transport processes from the land surface into the atmosphere need to be investigated to estimate weather phenomena and climate trends. To help fill this knowledge gap, we developed a drone-based aerosol particles sampling impinger/impactor (DAPSI) system for field studies to investigate sources and near surface transport of biological INPs. DAPSI was designed to attach to commercial rotary-wing drones to collect biological particles within about 100 m of the Earth’s surface. DAPSI provides information on particulate matter concentrations (PM10 & PM2.5), temperature, relative humidity, and air pressure at about 0.5 Hz, by controlling electrical sensors with an onboard computer (Raspberry Pi 3). Two remote-operated sampling systems (impinging and impacting) were integrated into DAPSI. Laboratory tests of the impinging system showed a 96% sampling efficiency for standardized aerosol particles (2 µm polystyrene latex spheres) and 84% for an aerosol containing biological INPs (Betula pendula). A series of sampling missions (12 flights) were performed using two Phantom 4 quadcopters with DAPSI onboard at a remote sampling site near Gosau, Austria. Fluorescence microscopy of impactor foils showed a significant number of auto-fluorescent particles < 0.5 µm at an excitation of 465–495 nm and an emission of 515–555 nm. A slight increase in ice nucleation activity (onset temperature between −27 °C and −31 °C) of sampled aerosol was measured by applying freezing experiments with a microscopic cooling technique. There are a number of unique opportunities for DAPSI to be used to study the transport of bioaerosols, particularly for investigations of biological INP emissions from natural sources such as birch or pine forests.
Highlights
Precipitation as a part of surface hydrology is the result of physical and chemical reactions taking place in the troposphere
Transport processes from the land surface into the atmosphere need to be investigated to estimate weather phenomena and climate trends. To help fill this knowledge gap, we developed a drone-based aerosol particles sampling impinger/impactor (DAPSI) system for field studies to investigate sources and near surface transport of biological ice nucleation particles (INPs)
Different types of INPs, many associated with microorganisms, are present in precipitation collected at the surface of the Earth [4,5,6]
Summary
Precipitation as a part of surface hydrology is the result of physical and chemical reactions taking place in the troposphere. The formation of ice in pure water is kinetically hindered at temperatures below the equilibrium freezing/melting point at 0 ◦C. Homogeneous ice nucleation, where the ice embryo consists of water molecules only, takes place at about −38 ◦C in micrometer sized water droplets [1,2]. -called ice nucleation particles (INPs) can act as triggers for freezing events at higher subzero temperatures. Heterogeneous ice nucleation based on foreign INPs occurs in clouds at warmer atmospheric layers, resulting in solid or mixed phase clouds with different properties [3]. Hydrological events in the form of hail, rain, snow, or sleet formation often result. Different types of INPs, many associated with microorganisms, are present in precipitation collected at the surface of the Earth [4,5,6]
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