the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Jun 2024
A modular approach to volatile organic compound samplers for tethered balloon and drone platforms
Abstract. Situated at a land-sea interface, Houston, Texas, is a national hub for the petrochemical industry and has the second fastest-growing metropolitan population in the United States. Addressing air quality in this region is uniquely challenging, due in part to its wide range of meteorological conditions (e.g., convection systems and temperature inversions) and continuum of volatile organic compound (VOC) and aerosol sources (e.g., anthropogenic and biogenic). As a result, Houston was chosen as the location for the Department of Energy’s Atmospheric Radiation Measurement (ARM) program-led Tracking Aerosol Convection ExpeRiment (TRACER), which investigated cloud and aerosol interactions in the deep convection over the area. Deployed as a key asset, ARM’s tethered balloon system (TBS) was used to investigate questions related to the vertical distributions of aerosols and their formation, including their precursor species volatile organic compounds. Platforms like TBSs and uncrewed aerial vehicles (UAVs) can bridge the vertical gap between ground-based and crewed airplane measurement platforms to focus on near-surface characterization. However, there has been limited effort to modularize and integrate VOC samplers into instrument payloads on both aerial systems. In this study, lightweight and robust VOC samplers were designed and deployed on the TBS and a UAV to collect VOCs in flight. The modular design allowed for scalable adjustments to meet the unique platform requirements and enabled multiple flights per sampling day. Each sampler can autonomously collect VOCs on up to four sorbent tubes for subsequent thermal desorption-gas chromatography-mass spectrometry analysis. The low sampler mass (2.2 kg and 800 g, TBS and UAV, respectively) enables the combination of these VOC samplers with trace gas, aerosol, and meteorological sensors on aerial platforms. These profiles allow us to assess temporal changes in VOC magnitude and composition at multiple locations. Observations from TBS and UAV flights during TRACER are presented and future considerations for sampler design and deployments are discussed.
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Status: open (until 21 Nov 2024)
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RC1: 'Comment on amt-2024-96', Anonymous Referee #1, 25 Jul 2024
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In their manuscript "A modular approach to volatile organic compound samplers for tethered balloon and drone platforms" (amt-2024-29), the authors present an instrument for collecting multiple sorbent tube samples that is suitable for drone- and balloon-based platforms. In general, this is a major topic in VOC sampling and the subject of many recent advances. The instrument described here is a nice addition to the suite of custom tools that have been developed throughout the research community. And the reported applications demonstrate the utility of these measurements To be suitable for publication, this manuscript should more fully examine the existing literature and explore what tools are out there. Many of the goals achieved in this work have been previously demonstrated. The authors are in a bit of a rock and a hard place, because many of the samplers previously demonstrated are not commercially available, so there is value to providing detail and demonstrating their own solution and I think it is still valuable to publish this work. However, with that in mind, I would have liked to see a little bit more of a demonstration of the science that will actually be achieved with this device and/or a demonstration of some of the next-step advances they describe as being possible and would advance the field. Specifically my two major concerns are described here:
(1) There are details missing on the technical aspects of this device. For example: it's overall weight and size are only in the abstract, the capacity of the battery is not provided, there is a lack of clarity about the control system (why a computer and a microcontroller?), whether power for the UAV version is being supplied by the UAV itself, how or if it is being integrated into the TBS payload, etc.
(2) The introduction overlooks prior work that demonstrated many of the achievements shown here, primarily multiple samples collected from a single airborne package. The authors elude to many promising features of their work, including communication with the ground, potential to integrate signals from other instruments, and complex sampling strategies. These advances would truly be novel and show the field what can be done, but are not really demonstrated here (and their theoretical possibility was mentioned in some of the previous literature). The authors should look a little more deeply into the literature (a few citations are provided, but I think there are others) and more thoroughly identify the gaps and how their work fits into that context.
Specific comments:Line 68-70. There have been at least some efforts (including work published in this journal) on independent, drone-compatible VOC samplers, both for collection of multiple coordinated samples across multiple platforms (DOI: 10.5194/amt-16-4681-2023), and for sequential samples within the same platform (DOIs: 10.5194/amt-12-3123-2019; 10.1016/j.jes.2024.04.016) as is being reported here. So this statement is not really true and highlights some need for a bit more literature review to place this work in the context of prior work.
Line 86-87. It's not clear what the author's mean by this statement. For example, commercially available options can monitor trace gas levels and use them as triggers for sorbent tube collection (see for example the SENSIT SPOD), and canisters have regularly been collected alongside comprehensive instrument payloads, includign with an arbitrary trigger for collection (DOI: 10.5194/amt-10-291-2017). What do the author's mean by "integrated" in this context?
Line 91: By "integration" in the ARM TBS payload, do author's mean they use the meteorological, aerosol, and ozone data to inform timing of sample collection, or just that they share a data aquisition system? The latter does not seem like a scientific advance, but rather solving a specific technoical issue relevant just to the TBS system. Throughout the work, it looks like this sampler only uses preset timing to determine sample intervals, so it's not clear to me that it is really "integrated" in any meaningful way.
Line 103-104. "uses lighter-than-air principles to obtain its initial lift" seems overly jargony/complex. I would say that the fact that helium-filled balloons rise can be considered common knowledge and does not need to be explained
Line 111. Authors should note the size range of particles measured by POPS, since later concentrations are provided just as total numbers
Line 131. The authors should clarify what they mean by modular. Which components can be separated and recombined in different ways?
Line 140. It's not really clear to me why there needs to be a computer on board. Why not just provide firmware to the Arduino and re-program it on the ground if necessary? Including the computer seems like extra weight and power. Or conversely, it looks like the UDOO Bolt has analog and digital I/O, so why include the microcontroller at all?
Line 147. How was flow controlled? Is flow checked on each tube, since their resistances could be different, or is it measured in real time? Also, no information about the pump is provided - what pump is being used?
Line 204. What do the author's mean the code initiation was synced? That the start time was synced with the start time of the flight?
Line 236. More information about this pairing would be helpful. Is the power for the UAV being directly used to power this device? And what communication features are being used. In general, more description of the "modularity" of this device would improve understanding of its uniqueness and value. This is later described in more detail in lines 254-256 and I agree ground-based communication with the device is a big step forward that I'm not sure has been previously demonstrated; this should be described earlier and/or in the methods.
Line 250. Was the use of metadata used here or demonstrated? Complex sampling strategies have been previously shown to be possible on the other samplers mentioned above, but the inclusion of other sensors, though likely possible in the other systems, would to my knowledge be a new advance worth demonstrating explicitly.
Line 266. "1 A" is not a unit of power, do the authors mean 1 Ah? What is the size of the battery?
Line 343. Could the authors estimate increase in mass due to each additional tube? This would involve the tube, valve, and lines, are there other components that would also need to be scaled?
Citation: https://doi.org/10.5194/amt-2024-96-RC1
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