| 15 Jan 2026
Exploring the Feasibility of an Air Sensor Array for the Real-Time Detection and Characterization of VOCs
Abstract. Volatile organic compounds (VOCs) are an important class of atmospheric chemical species that can be directly harmful to human health and contribute to the formation of hazardous secondary products. Measurements of ambient VOCs are typically made using “offline” techniques, which are well-suited for distributed measurements but have low time resolution, or real-time measurements using state-of-the-art in situ instruments, which have high precision and time resolution, but tend to be expensive and so cannot be deployed in a widespread manner. An alternative VOC measurement approach that is both real-time and lower in cost would open the possibility of widespread, spatially distributed measurements of VOCs in air quality and atmospheric chemistry contexts. While there are several commercially available air sensors that are sensitive to environmental VOCs, these sensors are “broadband,” meaning that each can only output a single scalar value that reflects the sensitivity of the sensor toward a wide and poorly defined range of VOCs. As a result, VOC air sensors have, to date, seen little use in research. Here, we investigate the feasibility of a novel method for measuring environmental VOCs that uses an array of such broadband sensors. This array includes VOC air sensors representing three fundamentally different sensor types, and takes advantage of operational parameters that achieve a diversity of responses amongst sensors with the same type. Within a controlled laboratory setting, we obtained calibration curves for ten typical atmospheric VOCs between 5 and 100 ppb and explored the effects of varying RH and introducing binary mixtures on sensor responses. Overall, we found that all observed sensor responses can be parameterized with linear or power-law models, consistent with results of prior studies and expectations based on physical sensing principles. Our results show that each of the 12 sensors in our array appear to have their own unique sensitivities to various VOCs, resulting in distinctive “fingerprints” of array responses for each compound tested. However, we also show that interferences by water vapor and other gases pose substantial challenges that likely cannot be fully addressed in the laboratory. Thus, co-location with a reference instrument in the field may first be required if this measurement approach is to yield quantitative, chemically specific information about ambient VOCs in indoor or outdoor environments.
This manuscript provides an interesting exploration of the varying sensitivities of different VOC sensors in an array. The plots are very clear and useful for considering how a multi-sensing-technology (PID, MOx, EC) array can be used to gather species (or species-group) specific information. However, this is not the first time sensor arrays have been used to measure VOCs, yet the manuscript does not seem to fully acknowledge much of the other work on VOC sensing and sensor arrays, making it difficult to fully assess the impact of this work. A number of suggestions are given below to better contextualize this work within the related body of VOC sensing efforts.
Line 78: More recent examples of e-noses should be given here, as there have been many developments in this space since 1994.
Line 83: You mention that sensor sensitivities to non-VOC gases are a challenge for VOC sensors. Why was this not explored in the present study, alongside the exploration of RH and VOC mixture impacts? If it cannot be added into the study, the reasoning for excluding it, as well as suggested avenues for testing these impacts, should at least be mentioned.
Paragraph starting on line 85: Examples of prior MOx sensor arrays are given. Examples of successful uses of PID sensors should also be mentioned (even if they are not arrays) to give context to the prior use of these sensors.
Line 97-98: There actually are examples using a range of sensing technologies that should be acknowledged here. Two examples: Xu, Linjie, et al. "Hybrid gas sensor array to identify and quantify low-concentration VOCs mixtures commonly found in chemical industrial parks." IEEE Sensors Journal 22.13 (2022): 13434-13441. And Fumian, Francesca, et al. "Development and performance testing of a miniaturized multi-sensor system combining MOX and PID for potential UAV application in TIC, VOC and CWA dispersion scenarios." The European Physical Journal Plus 136.9 (2021): 913.
There are also many examples of using sensor arrays with temperature cycling that are worth mentioning in the introduction, as they have provided another route to gain species-specific information using VOC sensors. One such example: Baur, Tobias, et al. "Field study of metal oxide semiconductor gas sensors in temperature cycled operation for selective VOC monitoring in indoor air." Atmosphere 12.5 (2021): 647.
Lines 125-126: This is not true. Temperature control has been used many times in VOC sensing. Mostly in indoor applications, but since this work is in a controlled laboratory setting, it cannot exclude indoor applications in its analysis: See above with work by Baur et. al., as well as He, Junjie, et al. "Low-cost MOX sensor for indoor ppb-level VOC detection using pulsed temperature-voltage dual modulation." Sensors and Actuators B: Chemical (2025): 138289. And Leidinger, M., et al. "Selective detection of hazardous VOCs for indoor air quality applications using a virtual gas sensor array." Journal of Sensors and Sensor systems 3.2 (2014): 253-263. And On the performance evaluation of hybrid and mono-class sensor arrays in selective detection of VOCs: A comparative study
Lines 138-140: This is also not true. VOC EC sensors have been used for methane detection (Silberstein, Jonathan, Matthew Wellbrook, and Michael Hannigan. "Utilization of a Low-Cost Sensor Array for Mobile Methane Monitoring." Sensors 24.2 (2024): 519.) and for VOCs: Mayer, Thomas, et al. "Toward an Event-Based and Quality-Assured Air Sampling: A Portable System for Sensing and Sampling Volatile Organic Compounds." Analytical Chemistry 97.43 (2025): 23765-23772.
Line 138-140: Although VOC EC sensors have indeed been used before (see above), they certainly are less common. Is there any explanation for why this is that can be added?
Lines 232-233: Why were these compounds chosen? Also, what are the typical ambient concentrations of these compounds? Is 5 ppb a reasonably low detection limit for all of these? It seems like some would often be much lower.
Figure 4 (and related discussion): This figure is really interesting, as it shows the different chemical “fingerprints” produced using the sensor array. However, these fingerprints are only clear when there is only one compound present. What happens in ambient air when there is a complex mixture of compounds? Prior work has used pattern recognition / machine learning to disentangle these effects. Some discussion of how the information provided by the array could actually be used in an environmental application is needed. The following reference provides some ideas for interpretation: Rath, Ronil J., et al. "Chemiresistive sensor arrays for gas/volatile organic compounds monitoring: a review." Advanced Engineering Materials 25.3 (2023): 2200830.
Line 302: Why were these two compounds chosen for the RH testing? Wouldn’t it have been more useful to choose two more chemically different species (i.e. an alkene and an aromatic) to understand how the effects vary more broadly? This choice should be justified.
Line 350: Again, why were two chemically-similar alkenes chosen for the binary mixture? Would the additive nature of the sensors also apply in a mixture that contains an alkene and an aromatic? It seems as if the response would be very different, which limits the applicability of these findings.
Lines 422-427: Sensor colocation with reference instruments and “novel application of data analysis techniques that directly interpret air sensor measurements” has already been done extensively with VOC sensors, which should be acknowledged. A few examples include: Hong, Gung-Hwa, et al. "Long-term field calibration of low-cost metal oxide VOC sensor: Meteorological and interference gas effects." Atmospheric Environment 310 (2023): 119955. , Frischmon, Caroline, et al. "Improving the quantification of peak concentrations for air quality sensors via data weighting." Atmospheric Measurement Techniques 18.13 (2025): 3147-3159. And Okorn, Kristen, and Michael Hannigan. "Applications and limitations of quantifying speciated and source-apportioned vocs with metal oxide sensors." Atmosphere 12.11 (2021): 1383.
Line 449: Discussion of how the “chemically specific information about VOCs” would actually work in practice is lacking. The fingerprints shown in Figure 4 are certainly interesting, but how would they be applied or used in contexts where there is a complex mixture of compounds (thereby making it difficult to distinguish the individual fingerprints).