Reducing methane emissions through identification, detection, measurement and quantification
- Identify known sources of emissions and survey for emissions
- Quantify sources of emissions directly by taking measurements or indirectly using a combination of measurements, calculations and models
- Create, update and periodically improve inventories of emissions
A key step in reducing methane emissions is to identify and detect sources of the emissions. Emissions that have been identified and detected are measured, quantified and recorded in inventories. These inventories serve as a starting point for prioritizing mitigation activities (measures to reduce methane emissions). Because of the wide range of sources of methane emissions in natural gas value chains, methods for identifying, detecting, measuring and quantifying emissions are varied. Methods include approaches that have been available for decades and approaches that are just emerging. The best practice to follow will depend on the characteristics of a facility and the cost-effectiveness of the methods. Best practice will also depend on the need for inventories, which may include introducing voluntary programs, developing detailed corporate inventories, or keeping to regulations that require particular methods to be used.
Identification and detection
Some sources of methane emissions are a known part of the design of natural gas systems. In these cases, analyses of a system’s design are used to identify emission sources. Other methane emissions are unintentional. Detection surveys need to be carried out to identify unintended sources and to confirm known sources. Detection methods may use passive or active sampling. They may detect at a fixed point or over an open path, and may involve imaging. The methods use a range of sensing technologies. Some methods apply to all sectors of the natural gas value chain. Others have more specialized uses. Because of the wide range of methods and uses, best practice for identifying, detecting, measuring and quantifying emissions will depend on the characteristics of a facility and the cost-effectiveness of the methods.
Measurement and quantification
Once emissions are identified and detected, a wide variety of methods can be used to quantify them. Methods often involve measuring methane concentrations in flows of gases or ambient air, but could also include a wide variety of other measurements (ranging from gas pressures to wind speeds). Emission rates can be quantified directly by carrying out measurements or indirectly through a combination of measurements, calculations and models.
Methods applied at a variety of scales
Emissions are identified, detected, measured and quantified using devices that are handheld, fixed at a location or fitted on vehicles, drones or aircraft, or by satellite. Large-scale emission estimates aggregated over many individual sources, are generally referred to as top-down assessments. Estimates of emissions from individual sources, which are then added together to produce estimates for a site or area, are generally referred to as bottom-up assessments. Bottom-up assessments provide detailed information about emissions from equipment and operations, but may miss some unexpected, unintended or uncharacteristic emission sources. Top-down assessments generally lack detail about individual sources but can provide comprehensive information about emissions at a site or in a region. Depending on the scale of the measurement, top-down measurements may include contributions from sources that are not a part of the natural gas value chain, and this needs to be accounted for when interpreting findings and reconciling top-down assessments with bottom-up estimates. Co-ordinated use of measurements at varying scales may provide more reliable quantification.
Programs to develop, update and improve inventories
Several methods are generally used in programs to identify, detect, measure and quantify emissions. The resulting information is recorded in emission inventories, which are regularly updated and improved. The continual improvement of inventories may include new methods of detecting and measuring emissions, new information on average emission rates from equipment, new emission models, or other innovations. Comparisons between top-down assessments and bottom-up assessments can guide continual improvement.