VSI - Model AS-111 -UAV-mountable Sorbent Tube Air Sampler

Measuring the gas composition and/or isotopic signature of air reveals crucial information about water use, carbon balance, greenhouse gas emissions or pollutants in natural or managed ecosystems or urban settings. UAV-systems could contribute to improved monitoring of atmospheric background levels and air quality, as well as improved modelling of net surface–atmosphere fluxes, by expanding the part of the lower troposphere that can be sampled. UAV thus also allow for sampling along vertical profiles in the lower boundary layer, which would otherwise require expensive eddy flux towers or the use of balloons. There is thus scope for UAV-mounted sampling systems to contribute to improved monitoring of GHGs and air pollutant emissions, which is of utmost importance when dealing with mitigation measures or enforcement of environmental laws. 

At the current configuration, the sorbent tube gas sampler for UAV can be loaded with four sorbent tubes (weight: 1200 g; dimensions:  180 x 155 x 130 mm (Lenght, Width, Height) with installed tubes). The sample gas inlet can be set with a manually adjustable pinch valve and maintained at 50 mL min−1 when e.g. using 6 mm thick Tenax GR packed sorbent tubes (see overview on sorbent tube types). All tubing is made out of 4 or 6-mm PTFE, and tube connections out of polyethylene terephthalate (PET) or metal. Passing the restriction valve at the sampler inlet, the gas flow is split in two using a Y connector and forwarded to the two inlet ports of an electric four-port gas distribution manifold. The gas manifold enables switching between different sampling modes, either loading all four tubes simultaneously, individually or allows for collecting subsequent duplicates. The sorbent tubes are installed at the outlets of the gas manifold using straight push-in connections. At the outlet of the four sorbent tubes, the gas flow is merged into two streams using a 90° push-in Y connector. Each stream then passes through a flow sensor, recording the actual flow rate. The gas streams are finally united and directed to the suction pump. To circumvent the non-regulated suction pressure of the pump, a tee piece is installed prior to the pump feed to equalise the different flow rates set at the restriction valve of the gas inlet. Thereby the exposure to pressure differentials resulting in altered flow readings, and the development of leaks and the overuse of sampler components is effectively prevented.

The VSI AS-111 sorbent tube sampler for UAV is equipped with a memory card, recording the actual flow rate, temperature, air pressure, humidity, the activated sample port number, and time over the sampling event. The gas sampler is triggered to gather a sample utilising a 5 V DC relay connected to an open-source autopilot. For example, the relay can be autonomously triggered with missions created (e.g. using Mission Planner GCS); e.g. by approaching within 2 m of a designated point. Here, the UAV can be programmed to delay and gather a sample for x seconds to sorption tubes. The UAV can subsequently fly to the next sampling point or height, or return and land. A sample can alternatively be collected manually, utilising the pilot's console transmitter. The sorbent tube sampler is mounted underneath the UAV fuselage between the landing gear legs using a quick release dovetail mount; 12 V DC power must be supplied to the VSI AS-111 sampler from the UAV.

The AS-111 sorbent system is able to carry sorbent tubes for a large range of air sampling purposes (see overview on sorption materials), for example the location and hight profiles of volatile emissions, pollen and particulate matter (PM2.5, PM10) concentrations. The sorbent sampling system is currently adapted to meet the demands of policing missions with heavy UAVs in the project C-SALS. Vienna Scientific is happy to contribute to the development of adapted sampling systems - meeting the air sampling needs of your research or environmental monitoring project