Outdoor air monitoring: Performance evaluation of a gas sensor to assess episodic nuisance/odorous events using active multi-sorbent bed tube sampling coupled to TD-GC/MS analysis
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The sampling of representative episodic events can be a difficult aspect (Caron et al.,2016, Ou-Yang et al., 2018), especially due to the short duration of episodic occurrences and its possibility of materializing during all hours of the day (Gallego et al., 2008). In this line, the activation (switching on) of the air samplers when an odour episode begins and the switching off of the apparatus at the end of the odour episode, together with the annotation of the time interval when the air sample has been taken, are key aspects. In some cases, the potentially affected people and municipality technicians can activate the samplers. In the same way, a mobile unit may also be handed to the local police in order to follow directionally changing episodes (Roca et al., 2003, Roca 2006, Gallego et al. 2008). However, due to the short time duration of episodes and the potentiality of their occurrence during small hours, this approach to episodic sampling is sometimes not appropriate. Additionally, a bias in sampling representativeness can be added by field personnel (Ou-Yang et al., 2018). In this line, air sensors can be very helpful in peak event identifications (Spinelle et al., 2017, Morawska et al., 2018), and their use to trigger the switching on and off a sampling device is an interesting and innovative technique. On the other hand, the identification of the specific VOCs that generate an odorous episode is an essential point for air quality evaluation. Active sampling of outdoor air using a sorbent-based method (the air is pulled through tubes filled with appropriate sorbents) allows a successful collection of VOCs in air, including a wide range of chemical families, such as alkanes, aromatic hydrocarbons, aldehydes, alcohols, halocarbons, esters, ketones, terpenes, ethers, sulfur and nitrogen compounds, and isocyanates, principally. A good combination of different sorbents allows the qualitative determination of a wide range of C2-C14 VOC, around 200-300 in a Standard urban sample (Ribes et al. 2007, Gallego et al. 2009a). In this manuscript we present the evaluation of the suitability of a commercially available metal oxide semiconductor gas sensor (TGS 2602, Figaro Engineering Inc.) for the activation of a VOCs sampler when episodic events of nuisance/odorous annoyance occur. Concentrations of VOCs in outdoor air during 24 hour and episodic periods were measured simultaneously during 14 days in El Morell, near the Tarragona petrochemical complex. Analysis of VOCs was performed by automatic thermal desorption coupled to capillary gas chromatography/mass spectrometry (TD-GC/MS). VOCs analysis of samples takes place offline, generating a small gap between the sampling and the obtention of the analytical results that can be extended between two to eight days maximum, based on a maximum storage time of samples of one week. VOCs analysis through TD-GC/MS is more time consuming than real time gas analysis (Heninger et al., 2018; Lemaine et al., 2018), however, a good programmation of the sampling and analytical processes allows a rapid obtention of the results. TD-GC/MS analytical methodology, previous to air sampling through multi-sorbent bed tubes, is a very sensitive, selective and reproducible technique, and grants very low limits of detection for the evaluated VOCs, implying a large number of identified compounds within a wide range of VOCs families (Ribes et al., 2007; Gallego et al., 2009a, 2018a), an indispensable aspect for air quality monitoring. In this line, TD-GC/MS has been widely used in outdoor air quality evaluations (Gallego et al., 2009a, 2016, 2017,2018a). This selective methodology allows good chromatographic separation, and identification and quantification of target analytes through their characteristic mass spectrum and quantification ions, respectively (Ribes et al., 2007).
CitationGallego, E. [et al.]. Outdoor air monitoring: Performance evaluation of a gas sensor to assess episodic nuisance/odorous events using active multi-sorbent bed tube sampling coupled to TD-GC/MS analysis. "Science of the total environment", 3 Agost 2019, vol. 694, p. 133752:1-133752:13
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