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

Abstract

In order to evaluate the performance of a commercially available metal oxide semiconductor gas sensor (TGS 2602, Figaro Engineering Inc.) for activating a monitoring system when a nuisance/odorous pollution episode of volatile organic compounds (VOCs) occur, a widely used active sampling methodology based on multi-sorbent bed tubes (Carbotrap, Carbopack X and Carboxen 569) and analysis through automatic thermal desorption-gas chromatography/mass spectrometry was used. Daily 24 h samples of multi-sorbent bed tubes were taken over a period of 14 days using an air collector pump sampler specially designed in the LCMA-UPC laboratory. Simultaneously, daily episodic samples were taken according to the activation of another LCMA-UPC sampler by the metal oxide semiconductor gas sensor. Sampling was done throughout January–February 2019 at El Morell (Tarragona, Spain), near the petrochemical area. All episode samples present higher concentrations of VOCs than 24 h samples, with an average ratio of 3.5 times for Total VOCs. VOC familial distributions present very similar values in 24 h and episode samples (r2 = 0.7466), correlating significatively (F-Snedecor, p < 0.05). A higher level of VOCs in the atmosphere in general, not derived from a specific compound or a VOC/s family/ies, seems to be the trigger of the activation of the sampler by the sensor. On the other hand, no significant correlations are observed between alcohols concentrations and relative humidity (F-Snedecor, p < 0.05). Additionally, Total VOCs concentrations in episode samples are in agreement with higher percentages of NE-SSE wind directions, coming from the petrochemical complex. Hence, these aspects validate the use of the evaluated sensor for its application for the activation of samplers in air quality evaluations when episodic events occur, an interesting and innovative technique. Thus, this study is an important contribution to the understanding of the performance of gas sensors and proposes an expansion of their field of use.