It is necessary to measure human-made methane sources to understand how much methane gas is produced in certain areas and what’s causing the buildup. Field and atmospheric monitoring of methane emissions can help researchers better understand regional trends and develop a helpful understanding of how best to control these emissions.
Methane is a highly flammable gas that can seep into buildings from various sources and cause problems, including property damage and injury to its occupants. Monitoring and measuring the methane concentration is vital to the health and safety of workers and building occupants in high-methane areas.
Methane monitoring is also critical for understanding the sources of methane emissions to reduce their impact on infrastructure and the environment.
There are two main measuring approaches to methane monitoring: bottom-up and top-down. Both are very useful for understanding a location’s general methane emissions situation. Before you build a home or occupy a structure, contact Arroyo Geoscience for a complete methane measurement performed by certified professionals.
How Emissions are Measured: The Bottom-Up and Top-Down Approaches
Research techniques for measuring and monitoring methane emissions differ in scope and use of equipment. The bottom-up method looks at specific sources of methane emissions, such as herds of cattle, landfills, or natural gas operations, to see how much methane gas they emit. From this small-scale perspective, scientists can offer a broader picture of methane gas emissions in the area.
The top-down measuring approach takes top-level atmospheric readings from the entire planet, a continent, a nation, or a region. It then applies a quantitative understanding of the emissions to get a broad picture of the methane released in the area.
This method provides a comprehensive view and must be combined with the bottom-up approach. Methane has a long atmospheric lifetime and spreads around the globe due to stratospheric winds; using both techniques together provides the most accurate measurements.
Bottom-Up Measuring Technique
The bottom-up measuring technique takes qualitative measurements from site-specific locations and multiplies them over time and by emission factors such as the type of source. These sources might include an area like a large landfill or microbiologically driven emissions from cattle herds. As these different sources have a wide variance in temporal and spatial factors, the precise measuring conditions must be tailored to the source of emissions.
Some of the techniques used to gather data in small-scale bottom-up measurements from different types of sites include:
Point Source Measurements
Point source measurements detect and measure emissions from a localized source, such as a leaky valve or a coal mine ventilation system. The gas flow rate is calculated by placing a calibrated bag with a known volume on the source so the amount of gas leaked can be precisely measured.
Chamber Techniques
Chamber techniques involve placing a small box, usually one cubic meter or less, on a source of methane, for example, a section of a manure pile or on an area of soil. This methane monitoring system calculates emissions by measuring the change in methane gas concentration in the box over a precise, short, timed series.
Micrometeorological Techniques
If the source of methane emissions cannot be easily captured in a bag or box, they can be measured using meteorological equipment. The data from fast-response methane sensors and wind speed and direction sensors are calculated using atmospheric transport modeling.
The measurement area, or footprint, must be large enough to account for spatial and temporal variation in the emissions. Scientists can use vertical and horizontal flux measurement techniques to get an accurate reading.
Perimeter Facility Line Measurements
Perimeter facility line measurements are done by equipping the perimeter of a site with tunable diode laser infrared open-path spectrometers to measure the methane concentration per meter of distance upwind and downwind of an area. The measurement is determined by calculating the difference between ventilation rates upwind and downwind of the site.
The techniques used to gather emissions measurements from larger sources like landfills, coal mines, or natural gas systems are customized for each source of emissions.
Enteric Methane
Enteric methane is produced by fermentation caused by microbes in the gastrointestinal tracts of animals. This methane can be released into the atmosphere by expiration, flatulence, or eructation. The gold standard of enteric methane emissions detection methods involves placing a sample animal in a chamber for three days, during which researchers feed the animals and remove their waste. Well-calibrated instruments measure their methane output, which can then be used as an average for all animals at the facility.
Petroleum and Natural Gas Systems
Petroleum and Natural Gas Systems measuring and monitoring cover a system from the wellhead to the fuel’s point of use. This monitoring does not account for the emissions from burning or using the fuel.
As there are numerous potential emissions sources along the supply chain, each source uses a combination of small-scale site-specific monitoring systems and larger-scale, system-wide measurements from airplanes flying over the infrastructure.
Landfills
Unlike other human-made sources of methane, landfill methane detection methods cannot use simple emissions calculations based on data multiplied by emissions factors. Soil factors, oxidation processes in the landfill, seasonal climate variation, and operational practices influence landfill emissions.
Researchers measure emissions using a series of techniques, including chambers placed at meter intervals at different times of the day, meteorological measurements, and mass balance readings from aircraft.
Coal Mines
Coal mines produce methane biogenically due to microbes in the coal seam or thermogenically during the coalification process. In other words, methane is a byproduct of the heat released by microorganisms as coal deposits are formed.
Underground mine emissions can be measured at the site of the ventilation shafts using site-specific techniques like point source measurements. For open-pit coal mines, the emissions can be measured using open-path Fourier-transform infrared spectroscopy, which is then analyzed using Gaussian-based plume dispersion modeling.
Top Down Measuring Technique
For more significant sources of methane, top-down measures taken on a large geographic scale are necessary. The exact techniques used will depend on how large the scale is. These measurements use atmospheric measurements of methane concentrations and quantitative calculations based on known methane sources and sinks.
Global Measurements
Measurements that encompass the entire planet are done using a few different methods. Since 1978, a series of 45 detectors across the West Coast of North and South America and on several Pacific islands have been taking measurements four times per year to gauge methane concentration in the atmosphere.
More recently, the Greenhouse Gases Observing Satellite (GOSAT) uses Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) to give higher resolution measurements planet-wide than specifically located monitoring stations.
Continental Measurement
The NOAA Global Greenhouse Gas Reference Network (GGRN) operates a group of 40 300-meter-tall towers located across North America to detect methane emissions in their local area. These towers combine to give a picture of the emission measurement continent-wide. Samples are also collected at 17 locations every 2 to 3 weeks using aircraft.
Regional Measurement
Different regions have adopted their own methane emissions detection methods to understand methane emissions in their local area. Cities like Boston, Los Angeles, and Indianapolis have all constructed tower sites similar to those used to measure continent-wide emissions in their local areas. These measurements show the ventilation rates for methane emissions and methane concentration at upwind and downwind locations.
These methane measurements have shown a pronounced regional emission variance and help pinpoint problematic sources of excessive emissions.
Arroyo Geoscience for Precision Methane Monitoring
Methane emissions pose significant problems for the planet, local communities, and building infrastructure. Methane is a dangerous gas, and a methane leak can seriously endanger the health and safety of people in an area.
The expert technicians at Arroyo Geoscience can explain how emissions are measured and thoroughly inspect an area to identify dangers for occupants or the planet. Our trained professionals will use up-to-date measuring techniques and monitoring technology and give you the most accurate readings possible for your site.
Contact us today for a detailed study of the methane in your area, and let our experts give you peace of mind.