Methane measurement at monitoring sites

Natural gas is quickly becoming one of the most used fuels globally, and is already the most common form of fuel used to generate electricity and for domestic use in the UK. In fact, the last coal burned for fuel within a UK power station was back in April 2020 which is the longest period without burning coal on a large scale since the late 1700s. Of course, there are some instances of coal being used on a small scale as fuel in the UK, but the amount is not considered significant when compared to the volume of natural gas utilised nationally every year.

Sources of methane

Natural gas is currently easier and cheaper to extract than many deep level coal seams, and it’s also usually preferred to drilling for oil. Natural gas is mostly made up of methane which is produced by decomposing organic matter which has long been sealed off from the Earth’s surface and is recovered through hydraulic fracturing. Natural gas produces half the carbon dioxide emissions of coal, and overall its use helps to reduce annual emissions.

Naturally occurring subterranean gas deposits are not the only source of methane in existence, in fact there are many sources which often require strict monitoring. For example, methane emissions are released through agricultural activities such as raising livestock, and methane is also released into the atmosphere as organic waste breaks down in landfills. In the previous decade, 576 million metric tons of methane were produced on average every year which is as potent as a greenhouse gas as 84 times that volume in carbon dioxide.

Two of the main natural sources of methane emissions are the world’s oceans and wetlands. If human activity did not produce additional methane emissions then the naturally occurring methane sinks would account for the naturally produced methane as part of a balanced system. Human activity upsets this balance and leads to the need for human-caused methane sources to be monitored and reported accurately over time so they can be properly managed and reduced.

Monitoring sources of methane emissions

Not only is methane monitoring important for environmental reasons, there are also important health and safety considerations that have to be made by plants handling methane which involve monitoring gas concentration levels. The reason methane is such a popular fuel is because it is readily flammable and burns relatively cleanly. Under normal conditions and at low concentrations, methane is quite harmless, but it can have explosive effects when it is pressurised or allowed to build up within a confined space.

How do monitoring sites measure methane? Monitoring sites make use of precise sensors throughout their systems to measure methane concentrations and pressures at any given location. Monitoring and measurement systems are small and relatively cheap, but they greatly improve health and safety conditions on site. All methane from landfills must be captured and either treated, or used as extensively as possible. Systems which handle methane gas can be vulnerable to leakage, and so it is important to ensure that the entire system can be monitored for changes in the localised methane levels.

In a more general sense, atmospheric methane monitoring takes place constantly at key locations nationally and internationally. While localised methane monitoring focuses on the operations of an individual plant or other commercial operation, these atmospheric monitoring sites are looking at the  general atmospheric concentrations of methane in order to assess trends in atmospheric composition over time.

In either case, methane measurement methods vary from instantaneous results measured over a very short time frame to long term monitoring. Long term monitoring is useful for looking into atmospheric trends while short term monitoring is generally used on a smaller more localised scale to monitor a single methane source. Methods include remote emissions observatories, sensor towers, aircraft mass balance and remote sensing, satellite imagery, handheld sensor devices, and vehicle mounted measuring and monitoring devices.

Measuring methane emissions can also take a modelled bottom-up approach such as:

Chamber techniques - samples are taken over time to measure the flux of methane gas on a smaller scale

Mass balance - samples are taken from within an enclosed space to measure methane emissions from a single source, such as a herd of animals

Micrometeorological sampling - samples are taken at the bottom of the atmospheric layer to determine concentration on a large scale

Perimeter line - samples are taken at various points along a perimeter to determine emissions within a set boundary