Synspec - Model Alpha 116 -Methane/TNMHC Analyser

Measurement in air must be done to know the concentration of the greenhouse gas Methane and of the general load of all other hydrocarbons. The greenhouse gas Methane is measured by a true direct measurement principle, no interference of other molecules. Applications are: general greenhouse gas monitoring, industrial site or city kerb site monitoring, waste dump sites monitoring, etc.

In the same measurement cycle the sum of all other hydrocarbons is determined to quantify the general air pollution. These hydrocarbons can come from all kinds of sources like nature, industry, traffic and households. This method covers hydrocarbons that will not be seen by standard GC technology, like oxygenated hydrocarbons. In ambient air the background Methane concentration holds a yearly mean of 1.86 ppm. The seasonal, regional and yearly variation means that values from around 1.5 ppm up to over 5 ppm can be expected from natural sources. From human activities, like waste dump sites and natural gas heating, these values can be higher.

The analyser is a gas chromatograph. It contains a compact oven with a column that separates Methane from total non-Methane hydrocarbons. The detector is the FID. The gas sample passes through a special layered packed column. The Methane (CH4) passes through and is first injected into the detector.

A short moment after this, the column is “back-flushed” and all other hydrocarbons pass to the detector. This results in two peaks generated by the FID: Methane and TNMHC peaks.

The measurements are done using true gas chromatographic separation. This prevents potential problems with catalytical conversion used in other indirect measurements. The FID detector starts very easily, provided the available gases are of good quality.

For the proper running of the system a good source of Methane-free zero air is required. Any zero air generator must run with a catalytic Methane scrubber and work at a temperature of at least 400^oC. An alternative is to use nitrogen as carrier gas and the zero air only for the detector air supply.