Magda Brattoli

Odour Detection Methods: Olfactometry and Chemical Sensors

The complexity of the odours issue arises from the sensory nature of smell. From the evolutionary point of view olfaction is one of the oldest senses, allowing for seeking food, recognizing danger or communication: human olfaction is a protective sense as it allows the detection of potential illnesses or infections by taking into account the odour pleasantness/unpleasantness. Odours are mixtures of light and small molecules that, coming in contact with various human sensory systems, also at very low concentrations in the inhaled air, are able to stimulate an anatomical response: the experienced perception is the odour. Odour assessment is a key point in some industrial production processes (i.e., food, beverages, etc.) and it is acquiring steady importance in unusual technological fields (i.e., indoor air quality); this issue mainly concerns the environmental impact of various industrial activities (i.e., tanneries, refineries, slaughterhouses, distilleries, civil and industrial wastewater treatment plants, landfills and composting plants) as sources of olfactory nuisances, the top air pollution complaint. Although the human olfactory system is still regarded as the most important and effective “analytical instrument” for odour evaluation, the demand for more objective analytical methods, along with the discovery of materials with chemo-electronic properties, has boosted the development of sensor-based machine olfaction potentially imitating the biological system. This review examines the state of the art of both human and instrumental sensing currently used for the detection of odours. The olfactometric techniques employing a panel of trained experts are discussed and the strong and weak points of odour assessment through human detection are highlighted. The main features and the working principles of modern electronic noses (E-Noses) are then described, focusing on their better performances for environmental analysis. Odour emission monitoring carried out through both the techniques is finally reviewed in order to show the complementary responses of human and instrumental sensing.

Gas Chromatography Analysis with Olfactometric Detection (GC-O) as a Useful Methodology for Chemical Characterization of Odorous Compounds

The gas chromatography-olfactometry (GC-O) technique couples traditional gas chromatographic analysis with sensory detection in order to study complex mixtures of odorous substances and to identify odor active compounds. The GC-O technique is already widely used for the evaluation of food aromas and its application in environmental fields is increasing, thus moving the odor emission assessment from the solely olfactometric evaluations to the characterization of the volatile components responsible for odor nuisance. The aim of this paper is to describe the state of the art of gas chromatography-olfactometry methodology, considering the different approaches regarding the operational conditions and the different methods for evaluating the olfactometric detection of odor compounds. The potentials of GC-O are described highlighting the improvements in this methodology relative to other conventional approaches used for odor detection, such as sensoristic, sensorial and the traditional gas chromatographic methods. The paper also provides an examination of the different fields of application of the GC-O, principally related to fragrances and food aromas, odor nuisance produced by anthropic activities and odorous compounds emitted by materials and medical applications.

Odour Impact Monitoring for Landfills

In the perspective of the improvement of life quality and citizens wellness, odour pollution is becoming a more and more relevant topic. In fact, among the variables that could influence the citizens’ sense of a healthy environment, odour emissions play an important role, as they deeply affect the human life quality and psycho-physical wellness. An odour is a mixture of light and small molecules, that are able to stimulate an anatomical response in the human olfactory system (Craven et al., 1996). The nose represents the interface between the ambient air and the central nervous system; in fact chemicals interact with the olfactory epithelium which contains different olfactory receptors and the signals are transmitted to the brain, where the final perceived odour results from a series of neural computations. The olfactory signals are processed also thanks to the memory effect of previous experienced smells, thus accounting for the high subjectivity of the odour perception (Freeman, 1991; Pearce, 1997). In this way the sense of smell permits to detect the presence of some chemicals in the ambient air and for this reason odour perception is sometimes associated with a risk sensation (Dalton, 2003; Rosenkranz & Cunningham, 2003) or however it represents an indicator of a not salubrious situation for people suffering for olfactory pollution. Although odours do not involve toxic effects for human health, they could cause both physiological symptoms (respiratory problems, nausea, headache) and psychological stress (Schiffman, 1998). For this reason in the last decade the scientific community has been developing an increasing attention for odour pollution, generally caused by different types of industrial activities such as tanneries, refineries, slaughterhouses, distilleries, and above all civil and industrial wastewater treatment plants, landfills and composting plants. Moreover, the proximity of these industrial plants to residential areas really affects the acceptability of such activities causing population complaints (Nicell, 2009; Stuetz & Frechen, 2001; Yuwono & Lammers, 2004). This paper focuses on the necessity of a proper management for odour emissions during the processes and the critical phases of landfills, and on the development of a proposal for a guideline to evaluate odour emissions and odour impact. So, the methodological approach of the guideline is described and compared with those commonly adopted in odour regulations.

Application of Artificial Neural Networks to a Gas Sensor-Array Database for Environmental Monitoring

A sensors array based on two different types of chemical sensors such as tin dioxide commercial sensors and carbon nanotubes innovative sensors developed in the ENEA laboratories to monitor gases (e.g., CO, NO2, SO2, H2S and CO2) of relevance in polluted air has been analyzed. Measurements of chemical sensing of the sensors array have been performed in laboratory to create a database for applying artificial neural networks (ANNs) algorithms to quantify gas concentration of individual air pollutants and binary gas-mixture. A total number of 3,875 data-samples based on 413 distinct gas concentrations measured by 14 gas sensors has been used in the database. The ANN performance has been assessed for each targeted air-pollutant. The lowest normalized mean square error (NMSE) of 6%, 9% and 11% has been achieved for NO2, SO2 and CO2, respectively. In the contrast, NMSE as high as 28% and 39% has been measured for CO and H2S, respectively. The aim of this study is the selection of an optimal set of gas sensors in the array for enhanced environmental measurements of gas concentration in real-scenario.

A Portable Sensor System for Air Pollution Monitoring and Malodours Olfactometric Control

A portable sensor-system based on solid-state gas sensors has been designed and implemented as proof-of-concept for environmental air-monitoring applications and malodours olfactometric control. Commercial gas sensors (metal-oxides, n-type) and nanotechnology sensors (carbon nanotubes, p-type) are arranged in a configuration of array for multisensing and multiparameter devices. Wireless sensors at low-cost are integrated to implement a portable and mobile node, that can be used as early-detection system in a distributed sensor network. Real-time and continuous monitoring of hazardous air-contaminants (e.g., NO2, CO, SO2, BTEX, etc.) has been performed by in-field measurements. Moreover, monitoring of landfill gas generated by fermentation of wastes in a municipal site has been carried out by the portable sensor-system. Also, it was demonstrated that the sensor-system is able to assess the malodours emitted from a municipal waste site and remarkably compared to the olfactometry method based on a trained test panel.

Odour Impact Assessment by a Multiparametric System (electronic Noses/ch4-nmhc Analyser)

Odour impacts are assessed according to two principal approaches: evaluation and estimation of the pollutant relapse on the territory and monitoring through standard methodologies. In particular, odour monitoring is characterized by a great complexity due principally to the strict association of odour pollution to human perception. The standardized methodology for the determination of odour concentration is represented by an instrumental sensory technique, the dynamic olfactometry, that is affected by some limitations. This methodology provides punctual odour concentration data and it does not allow to perform continuous and field measurements, useful for monitoring the industrial processes causing odour emissions. The need of carrying out a continuous monitoring having been encouraged the use of an odour surrogate monitoring, performed by specific or not specific instruments (chemical analysers or electronic noses). The surrogate measurements employment is based on the fact that the ratio of surrogate concentration to odour units must be relatively constant and known. This paper focuses on the development of a multiparametric system for the evaluation of odour impact caused by an industrial source. The system has been tested during olfactometric monitoring campaigns conducted at the industrial site, coupling the results of electronic noses. The purpose of the research work has been to find an indicator for the odour emissions produced by the examined industrial site, and to correlate it with odour concentrations. This study has allowed to demonstrate the real applicability of not specific instruments to odour continuous monitoring, useful to detect a change of state in operating conditions of industrial processes and control it.

A Gas Sensor Array For Environmental Air Monitoring: A Study Case Of Application Of Artificial Neural Networks

An array of commercial gas sensors and nanotechnology sensors has been integrated to quantify gas concentration of air‐pollutants. A variety of chemoresistive gas sensors, commercial (Figaro and Fis) and developed at ENEA laboratories (metal‐modified carbon nanotubes) were tested to implement a database useful for applied artificial neural networks (ANNs). The ANN algorithm used is the common perceptron multi‐layer feed‐forward network based on error back‐propagation. Electronic Noses based on various sensor arrays related to mammalian olfactory systems have been largely reported [1,2]. Here, we reported on the perceptron‐based ANNs applied to a large database of 3875 datapoints for environmental air monitoring. The ANNs performance has been individually assessed for any targeted gas. The response of the classifier has been measured for NO2, CO, CO2, SO2, and H2S gas. The NO2 characteristics exhibit that real concentrations and predicted concentrations are very close with a normalized mean square error (N...

Automated Collection of Real-Time Alerts of Citizens as a Useful Tool to Continuously Monitor Malodorous Emissions

The evaluation of odor emissions and dispersion is a very arduous topic to face; the real-time monitoring of odor emissions, the identification of chemical components and, with proper certainty, the source of annoyance represent a challenge for stakeholders such as local authorities. The complaints of people, often not systematic and variously distributed, in general do not allow us to quantify the perceived annoyance. Experimental research has been performed to detect and evaluate olfactory annoyance, based on field testing of an innovative monitoring methodology grounded in automatic recording of citizen alerts. It has been applied in Taranto, in the south of Italy where a relevant industrial area is located, by using Odortel® for automated collection of citizen alerts. To evaluate its reliability, the collection system has been integrated with automated samplers, able to sample odorous air in real time, according to the citizen alerts of annoyance and, moreover, with meteorological data (especially the wind direction) and trends in odor marker compounds, recorded by air quality monitoring stations. The results have allowed us, for the first time, to manage annoyance complaints, test their reliability, and obtain information about the distribution and entity of the odor phenomena, such that we were able to identify, with supporting evidence, the source as an oil refinery plant.

A Portable Gas Sensor System for Environmental Monitoring and Malodours Control: Data Assessment of an Experimental Campaign

A portable sensor‐system based on solid‐state gas sensors has been designed and implemented as proof‐of‐concept for environmental air‐monitoring applications, malodours olfactometric control and landfill gas monitoring. Commercial gas sensors and nanotechnology sensors are arranged in a configuration of array for multisensing and multiparameter devices. Wireless sensors at low‐cost are integrated to implement a portable and mobile node, that can be used as early‐detection system in a distributed sensor network. Real‐time and continuous monitoring of hazardous air‐contaminants (NO2, CO, PAH, BTEX, etc.) has been performed in field measurements by comparison of chemical analyzers from environmental protection governmental agency (ARPA‐Puglia). In addition, experimental campaigns of the integrated portable sensor‐system have been realized for assessment of malodours emitted from an urban waste site. The results demonstrate that the sensor‐system has a potential capacity for real‐time measurements of air‐poll...