Flux Hood Sampling for Odour & VOCs
The flux hood sapling method (also called flux chamber or isolation chamber sampling method) has been used to measure air emissions from surface impoundments like landfill and contaminated sites.
Emission isolation flux chamber sampling method is US EPA recommended method to estimate gaseous emission rates from area emission sources. The flux chamber method was found to be a reliable method for measuring volatile organic emissions from surface impoundments. A typical flux chamber is as shown in the following figure.
 
When sampling, a representative area of the source surface is enclosed by the isolation flux chamber. Then a controlled flow of clean sweep gas (normally nitrogen or odour- and hydrocarbon-free air) is released into the chamber, allowed to mix, and then released through the exits. Odour samples can be collected using a sampling drum to sampling bags from the sampling vent. For emission sampling and analysis of specific compounds such as VOCs, samples can be collected into obsorbent tubes using a vacuum pump or canisters.
It should be noted that the flow rates of both sweep gas and sampling are very important in determining the emissions. The sweep flow rates of less than 2L/min should not be used for chambers. It is also recommeded that the flow rate not be greater than 10 L/min. The sampling rate should be less than the flow rate of sweep gas. Otherwise the outside air would be drown into the chamber to dilute the sampling gas, which may result in inaccuracy of calculated emissions. It is better to make the sampling rate less than 3/4 of the flow rate of sweep gas.
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