NUS Method for Odour Measurement

The sense of smell, like the other human senses, apparently gives rise to the response whereby an observer can distinguish between successive odour concentrations when each is about twice (or one half) the intensity of the preceding one. The NUS method of odour measurement takes note of this human response and automates the manner by which changes in the odour concentration of an air sample is presented to an odour observer. Odour measurements are needed to underpin numerous decisions that will have to be made to reduce odour nuisance. Devices that are used to quantify odour concentrations (known as olfactometers) must be designed and operated in a manner that follows the unique way in which humans respond to changes in smell. 

Research by the Air Research Group of the Department of Civil Engineering, NUS, under two recently completed grants (RP960647 and 970649) has resulted in the development of a new world-class computerised dynamic olfactometer (shown in Figure 1) named the "Odormat". The device is the first fully-automated dynamic olfactometer developed in this region and conforms to the most stringent olfactometry standards in the world. The NUS Odormat is designed to enable odour concentrations of air samples to be measured in a high-quality controlled procedure such that results are reliable and accurate. All air flows and control valves are electronically operated with high precision and a software automates incremental changes in air flows and captures the responses of the odour panel in a data base. Threshold odour concentrations of gases can be determined with the device and with minor modifications, the Odormat can be used to gauge the sensitivity of the human nose. 

An odour sample is dynamically diluted by odour-free air in the Odormat and then emitted through one of the two "sniffing ports". The other port will emit clean air. Trained odour panelists (typically six) sniff the diluted odour sample as it is discharged from one of the two presentation ports and indicate the one that is different from the other. This approach is called "binary forced-choice". The panelists also declare if the selection was a "guess", "inkling" or "certain". The panel continues to the next set of two samples, one of which also contains the diluted odour sample, but presented at a higher odour concentration. This approach is called "ascending concentration series". With the Odormat, all operations of the flow mixing and setting are fast, accurate and are fully automated. 

The NUS method for odour measurement has been validated against the latest European CEN standard for olfactometry and the Odormat has been found to perform exceptionally well. The Odormat technology has been commercialised by Aromatrix Pte Ltd, a new spin-off company of NUS Technology Holdings Pte Ltd. International recognition of NUS odour research has been increasing since the successful sale of the Odormat to a company in Australia. Enquiries about the Odormat technology have come from countries around the globe, such as Jordan, Italy and Vietnam.

Figure 1: Computerised Dynamic Olfactometer..