Non-specific chemical gas sensor arrays for environmental monitoring of odour emissions: a review

Recent advances in sensor technology, signal processing and pattern recognition algorithms have led to the development of chemical sensing instruments housing one or more non-specific gas sensors. These instruments are often referred to as 'electronic noses' or 'artificial olfaction systems' since they measure a range of non-specific compounds that make up odorous emissions. Odours usually contain various odorous chemical compounds, some of which cause annoyance to local receptors. For this reason, odour measurement has often been considered more of an art than a science. Subjective sensory measurement using a human nose has been the accepted 'standard' for odour measurement. This chapter reviews the recent applications of non-specific gas sensor array technologies used for environmental monitoring of odours; including a brief history on odour measurement applications; the different types of sensors utilised in gas sensor array systems are categorised and reviewed according to their operating principles; a range of pattern recognition techniques, from simple statistical analyses to artificial neural networks, used for the purpose of odour identification and quantification is also discussed. Considerable work has already been carried out in a broad range of industries including agriculture, food, waste treatment, paper, and tannery operations. In addition, there are efforts to develop on-site or portable sensor array devices for real-time and continuous odour measurement, capitalising on the low-cost, non-invasive, operator-free advantages of non-specific chemical gas sensor array technology