Selective detection of hazardous VOCs for indoor air quality applications using a virtual gas sensor array

Abstract

Abstract. An approach for detecting hazardous volatile organic compounds (VOCs) in ppb and sub-ppb concentrations is presented. Using three types of metal oxide semiconductor (MOS) gas sensors in temperature cycled operation, formaldehyde, benzene and naphthalene in trace concentrations, reflecting threshold limit values as proposed by the WHO and European national health institutions, are successfully identified against a varying ethanol background of up to 2 ppm. For signal processing, linear discriminant analysis is applied to single sensor data and sensor fusion data.Integrated field test sensor systems for monitoring of indoor air quality (IAQ) using the same types of gas sensors were characterized using the same gas measurement setup and data processing. Performance of the systems is reduced due to gas emissions from the hardware components. These contaminations have been investigated using analytical methods. Despite the reduced sensitivity, concentrations of the target VOCs in the ppb range (100 ppb of formaldehyde; 5 ppb of benzene; 20 ppb of naphthalene) are still clearly detectable with the systems, especially when using the sensor fusion method for combining data of the different MOS sensor types.

Highly sensitive benzene detection with metal oxide semiconductor gas sensors – an inter-laboratory comparison

“…This approach has previously been studied for the selective detection of volatile organic compounds (VOCs), e.g. benzene in indoor air (Leidinger et al, 2014;Schütze et al, 2017). MOS gas sensors are very robust and sensitive devices (Morrison, 1981;Sasahara et al, 2004) sensitive to a broad variety of reducing gases.…”

Highly Sensitive and Selective VOC Sensor Systems Based on Semiconductor Gas Sensors: How to?

“…Furthermore, in addition to identifying and quantifying target gases, this approach allows sensor self-monitoring [36], which is a crucial aspect especially for applications in safety and security. For VOC monitoring, selective identification of hazardous VOCs down to concentrations of 1 ppb could be demonstrated even in a background of other VOCs of several ppm and against changing humidity using a commercial ceramic MOX sensor at least under lab conditions [14]; similarly, quantification of VOCs at low ppb levels was demonstrated with this approach both for MOS [26] and SiC-FET [15,37] sensors. Further approaches to improve the performance of semiconductor gas sensor systems with dynamic operation are optical excitation [27,28] and impedance spectroscopy [38] often applied to MOX sensors or gate bias cycled operation for GasFETs [39].…”

“…The different methods employed for increasing the selectivity can also be combined, for example, by integrating several dynamically operated sensors in a hybrid sensor array or combining gas pre-concentration (see below) with temperature cycling to boost sensitivity and selectivity. Especially temperature cycled operation (TCO) has proven a very powerful and versatile tool for various sensor principles (MOS sensors [14,[30][31][32], SiC-FETs [33], pellistors [34]), which is easily understandable as the chemical interaction between sensor and gas atmosphere is strongly influenced by the surface temperature. For example, some gases such as CO or H 2 will react at relatively low temperatures, while others such as CH 4 are more stable and thus require higher activation energies to cause a sensor reaction.…”

“…One candidate sensor principle for direct monitoring of even sub-ppb level VOC concentrations are metal oxide semiconductor (MOS) gas sensors [13,14], but gas-sensitive field effect transistors (GasFETs), e.g., based on silicon carbide (SiC-FET), have also proven their suitability for this task [15]. For simplification, we will concentrate on MOS sensors in the following discussion, but many aspects also apply to SiC-FET sensors, so the approach is presented for semiconductor gas sensors.…”

Novel method for the detection of short trace gas pulses with metal oxide semiconductor gas sensors

“…For some applications sensors and adaptable sensor arrays have been investigated (Leidinger et al, 2015;Roberts et al, 2014;Sasahara et al, 2007). The classification of various hazardous VOCs at ppb concentration level has been demonstrated by some of us in earlier works using metal oxide sensors combined with temperature cycled operation (TCO) and pattern recognition as well as with novel MOFbased micro-preconcentrators (Leidinger et al, 2014;Wilhelm et al, 2016). Under ideal conditions this facile approach allows low-cost, online measurements with sub-ppb accuracy (Leidinger et al, 2017).…”