Measuring the gas composition and/or isotopic signature of ambient air above plant canopies reveals crucial information about water use, carbon balance and greenhouse gas emissions of natural or managed ecosystems. For example, photosynthesis and respiration impart distinct isotopic signatures to the atmosphere that are used to constrain global carbon source/sink estimates and partition ecosystem fluxes. Increasingly, the ‘‘Keeling plot’’ method is being used to determine the carbon isotope composition of ecosystem respiration (d13CR) in order to better understand the processes controlling ecosystem isotope discrimination in general and to integrate environmental effects on dynamic canopy and ecosystem processes in specific.
To support these and similar measurements, we recently developed a device to automatically sample ambient air at different heights within/above forest and crop canopies. The air sampler is easily mountable on commercially available, unmanned aerial vehicle (UAV) such as drones or blimps and is fixed deployable within and/or above canopies for automatic sampling. If carried by UAV, sampling can be triggered by reached specific target heights and waypoints or manually, fixed units usually sample according to a predefined time schedule or following a manual or environmental trigger. With the current systems, air samples are stored in 12 ml pre-evacuated sample vials for later routine analyses of gas composition (with a mass spectrometer). Currently, six sample containers are positioned in an revolver system (to be UAV deployable). However, larger numbers of sample vials can be easily achieved in units for fixed deployment (ground, within canopies, on tower systems, height transects, etc) or to be carried by larger drones or airplanes. The product originates from an ongoing collaboration with the Austrian Institute of Technology GmbH (AIT; PD Dr. Rebecca Hood-Nowotny) and the IAEA (CRP D1.20.13). The suitability of the sampling system to measure isotopic signatures at relevant concentration of CO2 in ambient air samples has been confirmed by initial tests (R2 = 0.972) conducted at the AIT. In addition to scientific questions, the automatic air sampler could be used to sample emissions from sources that are otherwise difficult and/or dangerous to sample using traditional methods. Connected to any kind of commercial drone (payload min 1.0 kg), the air sampler opens a whole new dimension in air sampling.
Future developments of the air sampling system will include the collection of condensed water samples from ambient air and the adaptation of the automatic sampling system to automatic chambers for soil efflux measurements (CO2, CH4, NOx determination etc.).