Odour sampling allows us to transfer odour from its source and transport it to laboratory conditions for olfactometry analysis. The complex process requires expertise, experience and most important, the right equipment.
Odour Surveys and Sampling
At Silsoe Odours Ltd our odour samples are placed in NALOPHAN sample bags, using PTFE sampling tubes. This model utilises the ‘lung principle’: sample bags fitted inside rigid barrels that are partially evacuated to create a vacuum, generated by portable 12v battery-driven pumps. The sample air is drawn along the tubes into the bags.
Where we are required to survey the source of the odour, such as compost, fields, or liquid surfaces, we will use a Lindvall hood for sample collection. This method requires that we cover a portion of the surface with a suitable ventilated hood, (following guidance in the EA draft H4 document). The odour sample is collected at the outlet of the hood. When collecting odour samples from liquid surfaces the Lindvall hood can be adapted by using floats.
Key to the process is the emission rate from the surface source, which is calculated by monitoring the air speed under the hood and adjusted by 0.3 m/s for each sample, creating a flow rate which is used to calculate the specific odour emission rate per unit area, per second as the following equation demonstrates:
Esp = Chood x L x V
Chood is the odour concentration measured from the sample bag.
L is the hood factor, which is equal to the path length (m2) of the hood divided by the covered area (m2).
V is the velocity (m/s) of air presented through the hood.