On September 22 and 23, a new meeting of CEN/TC 264/WG 41, that is, the Working Group 41 of the Technical Committee 264 on Air Quality of the European Committee for Standardization, took place. The agenda for the day included several items, but in the end, draft 3, which deals with field validation, took up most of the group's working hours.
The WG41 is working in three standards: 1) Instrumental Odour Monitoring Systems (IOMS) - Part 1: Definitions and general aspect; 2) Instrumental Odour Monitoring Systems (IOMS) - Part 2: Technical specifications and QA/QC requirements and 3) Instrumental Odour Monitoring Systems (IOMS) - Part 3: Field validation. This last draft has not been discussed during the second stage of the development of the standard until now. But the experts took the challenge and a text was delivered on time to activate the 3 PWIs, which is the next step in the CEN process.
The validation protocol requires the collection of data under varying conditions such as temperature, humidity, and background chemical interferences. These environmental influences can significantly affect sensor responses, making it important to evaluate IOMS accuracy, sensitivity, and specificity within defined operating cases.
The draft explicitly address the three primary measurement tasks of the IOMSs: 1) detection of odour presence/absence, 2) classification into odour classes, and 3) quantification of odour concentration. Each task needs specific validation procedures, employing statistical methods such as confusion matrices, sensitivity, specificity, and confidence interval estimation, in order to quantify detection capabilities and classification accuracy. One of the key topics in this standard is: What is the odour under study?
For detection validation, the performance parameters defined in the draft of the standard are, at this stage, sensitivity and specificity.
In odour classification tasks, the standard prescribes that IOMS outputs, expressed as odour class indicators, be validated against human panel assessments. The validation employs a multi-class confusion matrix to determine the sensitivity and specificity for each odour class, ensuring that the system can discriminate among multiple odour types
Quantification validation requires comparison of IOMS estimated odour stimulus metrics against reference odour concentrations obtained through dynamic olfactometry, following EN 13725. Samples designed to get the relevant concentration ranges are analyzed. In this case The Olfactory Stimulus Indicator (OSI) is validated against the reference odour concentration using the Bland-Altman method applied in the logarithmic domain.
Both detection, classification, and quantification must be reported in a specific and consistent format defined in this draft standard.
Finally, a chapter addressing the use of citizen science data for the validation of IOMS is included. This chapter is provided in an annex, which is currently designated as informative only.
If you find this article interesting, you might also be interested in these articles:
- First Meeting of the CEN group dealing with gas sensors and pattern recognition.
- The long and winding road of CEN/TC264/WG41 developing a standard for validating Instrumental Odour Measurement Systems
- Re-started the work of the WG41
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