Volatile Organic Compound Monitoring during Extreme Wildfires: Assessing the Potential of Sensors Based on LbL and Sputtering Films

Abstract

A new theory suggests that flammable gases generated by heated vegetation, in particular the volatile organic compounds (VOC) common to Mediterranean plants, may, under certain topographic and wind conditions, accumulate in locations where, after the arrival of the ignition source, they rapidly burst into flames as explosions. Hence, there is a need for the development of a system that can monitor the development of these compounds. In this work, a sensor’s array is proposed as a method for monitoring the amount of eucalyptol and α-pinene, the major VOC compounds of the Eucalyptus and Pine trees. The detection of the target compounds was assessed using the impedance spectroscopy response of thin films. Combinations of layers of polyelectrolytes, such as poly(allylamine hydrochloride) (PAH), polyethyleneimine (PEI), poly(sodium 4-sytrenesulfonate) (PSS) graphene oxide (GO), and non/functionalized multiwall nanotubes (MWCNT-COOH or MWCNT), namely, PAH/GO, PEI/PSS, PEI/GO, PAH/MWCNT, PAH/MWCNT-COOH, films, and TiO2 and ZnO sputtered films, were deposited onto ceramic supports coated with gold interdigitated electrodes. The results showed that concentrations of the target VOCs, within the range of 68 to 999 ppmv, can be easily distinguished by analyzing the impedance spectra, particularly in the case of the ZnO- and PAH/GO-film-based sensors, which showed the best results in the detection of the target compounds. Through principal component analysis (PCA), the best set of features attained for the ZnO and PAH/GO based sensor devices revealed a linear trend of the PCA’s first principal component with the concentration within the range 109 and 807 ppmv. Thus, the values of sensitivity to eucalyptol and α-pinene concentrations, which were (2.2 ± 0.3) × 10−4 and (5.0 ± 0.7) × 10−5 per decade, respectively, as well as resolutions of 118 and 136 ppbv, respectively, were identified.

Graphene Oxide Thin Films for Detection and Quantification of Industrially Relevant Alcohols and Acetic Acid

“…Impedance spectroscopy was the analytical technique selected for the characterization of sensor units’ response to the industrial solvents mentioned above. Detailed information on experimental setup has been described by Magro et al [ 30 ]. Basically, a custom-made chamber with a volume of 58 L was employed to create a controlled atmosphere and assess the electrical impedance response of the thin films.…”

“…Aiming to circumvent the mentioned limitations, the development of sensor array-based systems dedicated to specific scenarios has gained relevance as a cheaper and simpler solution [ 28 , 29 ]. These systems enable an accurate and rapid qualification and quantification of VOCs through the interactions that occur on the surface of the sensor when they experience contact with the analyte [ 30 , 31 ]. Due to their flexibility and scientifically relevant results, sensor array-based systems have proved their suitability for the assessment of common VOCs such as acetone [ 32 ], ethanol [ 33 ], butanol [ 34 ], formaldehyde [ 35 ], triethylamine [ 36 ], methanol [ 37 ], isopropanol [ 38 ], ethyl acetate [ 39 ], benzene [ 40 ], or acetic acid [ 41 ], among many others.…”

“…The development of electronic tongues [ 42 , 43 , 44 ] and noses [ 30 ] based on featured organic thin films of graphene as sensing units have been widely addressed over the past years; an approach that can also be used for the development of VOC-dedicated electronic noses and tongues. For these cases, a sensor array is normally required.…”

Long-term in situ air quality assessment in closed environments: A gas chromatography–ion mobility spectrometry applicability study

“…24,25 In a different approach, multi-sensor array-based systems have equally been deeply studied regarding their suitability for the complete assessment of VOCs. 26,27 Nonetheless, all the mentioned techniques and procedures lack some features that are important in the field of VOCs assessment in the indoor air of closed environments, namely, the lack of portability, which hinders in situ analyses; the necessity of additional preparation of the sample, which increases the complexity of the analyses; the lower resolution power, sensitivity and selectivity, that inhibit the detection of VOCs at trace levels of concentration; the incapacity for real-time measurement, which delays the entire analysis; the necessity of trained personal due to the instrumental complexity, and several other limitations. 24,28,29 An analytical technique that has gained significant recognition in the detection, identification and quantification of VOCs is ion mobility spectrometry (IMS).…”

An Effective Sensor Network System for Early Wildfire Detection: Empowering Communities using Advanced Technologies

“…Through continuous monitoring of temperature, humidity, barometric pressure, and VOC gases, our sensors can swiftly identify abnormal conditions that may indicate the presence of a wildfire [11]. This real-time analysis enables prompt alerts and facilitates timely response measures to mitigate the impact of wildfires, thereby protecting lives and properties.…”