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Determining odour immission with the mobile electronic nose
With our mobile electronic nose, we swiftly and easily determine the pattern of odour immission on site to arrive at new insights.
Mobile electronic nose
An electronic nose – also called an eNose – is a portable device consisting of one or more sensors that respond to variations in the concentration of gases or volatile particulate matter that cause odour.
At OLFASCAN, we use an electronic nose from the Dutch company Comon Invent. The same type is used in the Port of Rotterdam's early warning system, among others. The eNose is equipped with 4 MOX sensors that respond to a wide range of components through a resistance change.
In addition, our eNose is equipped with a rechargeable battery that provides autonomy and a GPS module that records location. The eNose can be used both to obtain an odour map (heatmap) and to sketch a course as a function of time (stationary).
Geographic mapping
The electronic nose records sensor readings every 15 seconds, which together with the GPS data can be plotted on a map as points. At a normal walking pace, this reaches a point about every 20 meters.
To increase the spatial resolution, interpolation between points is used to produce a heatmap showing in which areas more or less VOCs were detected.
Geographic mapping – an example
In this case, the eNose was included during a sniff measurement around 4 water basins from which odour was released. During the measurement, the wind blew in from the west. The white points shown represent the intensities observed by the sniffers while the blue-red trace (blue: weak signal, red: plug signal) represents the signal from the eNose.
Lastly, the odour plume is also depicted. Both by eNose and sniff measurement, basin 1 was identified as the main odour source. The data obtained from the eNose tallies strongly with the observations Even at the farthest point, the eNose still measures a slight increase in odour concentration. As such, the eNose can be used to quickly display the measured odour graphically on a map.
Measurement in accordance with time
The eNose can also be used to monitor odour immission over time. In this case, the eNose is placed stationary and the odour is monitored for a period of time. To find out during which stage of a production process odour is released, the eNose was placed near the emission point.
The figure shows that odour emission is low until a few moments after the reactors are started up and marked fluctuations in odour immission are measured in the environment.
Restrictions
The eNose is not a universal solution for determining all types of odours and VOCs. It is not selective, and it displays higher sensitivity to some components than to others. Nor is it possible to link to exact odour concentration or component concentration, making the technique non-quantitative. The eNose is a relative measuring instrument that allows comparison of the odour concentration of one type of odour at different locations and times.
It is not a chemical analysis technique, meaning it does not show which components cause the odour. In order to find that out, a VOC screening is indicated. Finally, temporal and spatial resolution is limited in that when multiple contributors to odour are close together, the eNose will not be able to distinguish between them.
Conclusion
The mobile eNose is a valuable tool that we regularly use to get a global picture of odour immission into the environment. The tool complements traditional methodologies; correct interpretation of data requires care. It provides the possibility to measure odour over longer periods of time, or spatially display where the odour sources are located so that selective analyses with e.g. TD-GC-MS can be applied at targeted locations/moments.
How can we help?
If you’d like additional information, or have a specific question for one of our staff members, be sure to get in touch through our contact page.