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Comparing the Advantages and Limitations of Different Techniques Used to Quantify Methane Emissions From Municipal Solid Waste Landfills - 2.1 Flame Ionization Detection

2.1 Flame Ionization Detection

A flame ionization detector (FID) is a gas detector commonly used to measure methane concentrations.  Anair sample enters the device, and is combusted by a hydrogen flame.  There are two charged electrodes in the device, a positively charged nozzle head and a negatively charged collector plate.  The flame is produced at the nozzle head, and the collector plate is a tubular electrode above the nozzle head to which the ions generated from the chemical combustion reaction are attracted.  When the ions hit the plate, a current is induced, measured with a high-impedance picoammeter, fed into an integrator, amplified, and converted into a digital reading of ion concentration.  This ion concentration has been shown to be proportional to the concentration of the gas species (Chasteen 2009).

 FID Diagram

FID Diagram (Harvey 2017)

FIDs are relatively common due to their many advantages. The detector is low cost and extremely accurate for the measurement of methane and other hydrocarbons (Chasteen 2009). Additional benefits include that it has a wide linear range of 107 (Li et al. 2016), and it is not affected by small changes in the flow rate of the carrier gas (Golden). Alternatively, FIDs also have many limitations. The device is destructive to the sample (Golden), and it is a single-point measuring technique as opposed to an open-path technique that can collect emission data over a large area (such as a landfill surface) (USEPA 2011). Also, the detector requires a constant hydrogen supply for the flame (TSI 2013), and it is only capable of measuring the concentrations of non-oxygenated organic carbon compounds. This means that other gases such as hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, ammonia, or water vapor are undetectable (Golden; Li et al. 2016).

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