The use of their water-vapor-constrained bias correction led Houweling et al. All of these open-air techniques have the advantage of being able to measure methane emissions from a source area without disturbing animals or altering ambient conditions. Absorption spectroscopy using reflected sunlight (sensitive to entire atmospheric column) or thermal emissions (less sensitive to boundary layer). (2014a), and Katzenstein et al. [2] Actually, there are several conventions for what the standard temperature is, including 0 C, 70 F, and 25 C. The wonderful thing about standards is that there are so many to choose from. Figure 3.3 compares whole-landfill methane emissions for an Indiana landfill using an aircraft mass balance technique, tracer correlation, and modeled monthly emissions with and without oxidation (Cambaliza et al., 2017). Methane (CH 4) is an odorless and colorless gas, which is produced for example by livestock, landfills and swamps. However, constant or decreasing emissions paint a different picture. When these conditions are met, the SF6 tracer technique can produce accurate methane emission data from a large group of animals. Instantaneous to annual or multiyear averages, Generally reported as annual averages for inventory purposes from limited time duration data collected at various temporal scales, Involves use of models and assumptions as well as molecular and isotopic tracers, Calculated from source-specific activity data, Measurements reflect all sources that contribute to observed atmospheric concentrations, May not account for all sources in a given region. Capturing the temporal variation in emissions can also be difficult because chambers may not be able to be deployed for long periods of time because the disturbance to the ambient atmospheric conditions is too great. For example, a comparative study of methane emissions from two adjacent Wisconsin landfills using five methods (Babillote, 2011) included (1) tracer correlation using N2O, (2) an optical remote sensing method (VRPM), (3) static chambers with stable C isotopes to quantify soil oxidation, (4) an eddy covariance micrometeorological method, and (5) differential absorption Lidar (DiAL). In the case of open path laser systems, the measured quantity is actually proportional to the distance the laser travels through the gas before being detected. Using modern sequencing techniques, new insights into methane-oxidizing landfill soil microbial communities are also emerging. In the petroleum industry, amounts are given by volume, commonly as trillions (10 12) of cubic feet (ft 3) or TCF and billions (10 9) of ft 3 (BCF) in the United States. Houweling et al. (2003) to propose that global methane was reaching a steady state during the late 1990s and early 2000s. At spatial scales in between an individual source and a source region (e.g., total emissions from a large complex facility such as a natural gas processing plant, an animal feeding operation, or a large regional landfill), emission estimation might be considered either top-down or bottom-up or both. Current satellite instruments have been shown to have persistent biases in space and time (e.g., Bergamaschi et al., 2013; Houweling et al., 2014) that must be accounted for if satellite data are to be assimilated into atmospheric inverse models. Written out, 1 quadrillion is a 1 followed by 15 zeros: 1,000,000,000,000,000. A later study using the same WRF-STILT model configuration concluded that for 2007 and 2008, anthropogenic emissions were significantly underestimated for North America (Miller et al., 2013). Large reductions in emissions from high-emitting facilities, compared to measurements made in early 1990s (. The measurements were . You can view more details on each measurement unit: molecular weight of Methane or mol The molecular formula for Methane is CH4. Compared to underground mines, the level of emissions from the surface mines is much lower, primarily owing to low gas content of shallow coals that are mined from the surface. Because of the high spatial and temporal variability of diffusive emissions from landfill surfaces, generally poor matches are observed between predicted and measured downwind methane concentrations using standard dispersion models. In the 2017 GHGI, well completion emissions, including well workovers with hydraulic fracturing, were estimated to be about 0.03 Tg (an average of 2 metric tons per well). New Source Performance Standards for Greenhouse Gas Emissions From New The main advantage of respiration chambers is that (1) they are accurate when properly calibrated and operated, (2) all methane emissions, including from the anus, are captured, and (3) measurements take place continuously over several days, accounting for diurnal variation in methane emissions. On the other hand, CO2 emitted through the burning of fossil fuels (i.e. Estimates of surface mine emissions are based on coal production data, often imprecise gas content, and assumed gas emission factors. Inverse modeling has also been used to estimate emissions at urban and petroleum and natural gas basin scales. underground mine closings in recent years (e.g., decline from 523 in 2014 to 465 active mines in 2015 [EIA, 2016]) warrants efforts to improve emission estimates from this category. Major field campaigns and process-based model development have occurred in recent years, providing important new results quantifying methane emissions from landfills and providing improved inventory approaches. Uncertainties in top-down emission estimates are influenced both by uncertainties in atmospheric methane measurements and by uncertainties in the models used to estimate emissions based on atmospheric measurements (Box 3.1; for more detailed discussion of uncertainties, see Chapter 4). Therefore, emission measurements are not required for surface mines, and mine-specific emission data are rarely available. This method does not account for methane exhaled through the lungs. Quantifies rates for soil oxidation of atmospheric methane (i.e., negative emissions resulting from high soil oxidation capacities). Jump up to the previous page or down to the next one. Atmospheric methane by infrared spectrometry at precise infrared wavelengths for pristine sites remote from population centers. With improving spatial resolution and temporal coverage, satellite data may also help identify key regions where the largest discrepancies between observed and expected (based on inventories) methane abundances exist. These measurements will therefore lead to information about emission sources that is limited to midday hours, and these emissions may be different than at other times of day, which limits direct comparisons with methane inventories such, TABLE 3.5 Comparison of Top-Down and Bottom-Up Approaches to Estimating Methane Emissions That Introduce Challenges in Estimating Emissions Using Both Approaches. (2015a) found that emissions per controller varied by more than an order of magnitude between controllers in different types of service (e.g., separator level control versus controllers on process heaters). Time-series measurements of concentrations, analyzed by eddy covariance or by inverse modeling. Methane emissions from ventilation systems are assessed based on the airflow and the methane concentration in the ventilation air. Jeong et al. Gas concentration can be measured by a variety of techniques, including small gas detecting chips, sniffers that use gas spectroscopy to measure concentration in a known volume, and laser sensing systems that measure the absorption of a probe beam by a cloud of gas. These tables do not explicitly address uncertainties; however, TABLE 3.2 Top-Down Techniques for Measuring Methane Emissions. Environmental factors such as temperature, wind velocity (particularly important for grazing conditions), and humidity can affect the accuracy of the measurements). Over 100 countries signed on to the Global . (2018) also demonstrated the value of having a relatively dense network of quasi-continuous measurements; they were able to use a network of 18 sites, as well as additional sites with less-frequent discrete sampling. They concluded that the bottom-up emissions of EDGARv32FT2000 for North America were in good agreement with their top-down results. Imagine you have two bathtubs. Tower-based vertical measurements of gas concentrations and atmospheric parameters with standard modeling approaches to calculate fluxes. The attractiveness of this approach (also referred to as the sniffer method) is that emissions can be measured in on-farm conditions and on a large number of animals. Likewise, the study by Zhao et al. Of course, it is also possible to measure gas flow rates remotely using, for instance, hyperspectral imaging, as our LeakSurveyor instrument does. In 2013, the Environmental Defense Fund organized a coordinated top-down and bottom-up measurement campaign in the Barnett Shale petroleum and gas production region in north central Texas. These higher-resolution instruments may allow for mass balance approaches to be used to estimate emissions with higher spatial resolution than is currently possible. Go to the equivalencies calculator page for more information. These types of observations have revealed significant regional variability in the intensity of methane emissions (units of methane emissions per unit methane produced) from petroleum and gas supply chain sources. (2013) compared the carbon dioxide method to respiration chambers and found a significant underestimation of emissions by the carbon dioxide method. Carbon has a mass of 12.011 u and hydrogen has a mass of 1.008 u. A single flare measured had intermittent high emissions. Within each of these categories, a variety of subcategories of sources may exist with variability in emissions among the subcategories. Highest-emitting 10% of sites (including two high-emitting sources) contributed 50% of aggregate methane emissions. More recently, an automated head chamber system, GreenFeed (GF), was developed for spot sampling of exhaled and eructated gases (Zimmerman and Zimmerman, 2012). Aircraft-based measurements downwind of production region (but not upwind); methane measured using high-precision, high-time-resolution instruments. In these instances the ventilation rates can be estimated using a carbon dioxide balance or tracer gas technique. This area of influence is called the footprint and is dependent on factors such as measurement height, roughness height, stratification, the standard deviation of the lateral wind component, and wind velocity. These updates, while important in improving the accuracy of emissions documented in the GHGI, can lead to fluctuations in the GHGI from year to year (Figure 2.9). Monitoring observations of some nonmethane hydrocarbons are currently being made in NOAA/ESRL air samples by both NOAA and INSTAAR, and by UC Irvine, and as in situ measurements at AGAGE stations. Efforts to develop direct methane measurements or mine-specific assessments in surface coal mines of the United States and elsewhere have also been attempted. Most of these tech-. (2014) addressed the most important sources of error, and the modified technique produces methane measurements with accuracy similar to measurements using respiration chambers. Methane analyzers use IR methodology to measure methane gas. For instance, one popular old-school approach for measuring natural gas emissions is bagging: one places a bag of a known volume over the leaking component, and times how long it takes to fill up. Since 2013, however, a number of studies have reported new emission factor data for petroleum and natural gas. sampling across subpopulations may be impossible due to expense, study extent (e.g., geographic extent of study region), or restricted access. The most common strategy involves use of a Lagrangian particle dispersion model, such as the HYSPLIT (Hybrid Single Particle Integrated Trajectory Model; Draxler and Hess, 1997) or STILT (Stochastic Time-Inverted Lagrangian Transport; Lin et al., 2003) models, to simulate the backward trajectories of particles from measurement locations, keeping track of cumulative contact with the surface layer where emissions can influence the trace species concentrations in air parcels. Measures total methane emissions from variable-sized source areas. 1 m 3 liquid. Air samples have been collected from a variety of platforms including cargo ships, small aircraft, and tall telecommunications towers. The NOAA Cooperative Air Sampling Network is a subset of the NOAA GGRN. Methane measurements and emission estimates occur along a spectrum of spatial and temporal scales ( Figure 3.1 ), from large-scale global assessments of annual emissions to small-scale measurements of emissions from individual sources over short timescales (e.g., instantaneous). Both have faucets that are on and water is flowing. In general, the 13C of emitted landfill methane can range from 60%0 (negligible oxidation) to 30%0 due to oxidation (Bogner et al., 1997, 2011), generally negating its value for fingerprinting landfill methane in atmospheric studies. The eddy covariance technique calculates fluxes from rapid measurements of the vertical wind speed and gas concentrations (Harper et al., 2011; Prajapati and Santos, 2017). Emissions from ruminants and manure were found to be as much as a factor of 2 higher than estimated by the EPA and EDGARv4. underground mines by various research groups in the United States and elsewhere (Kirchgessner et al., 1993; Lunarzewski, 1998). Not a MyNAP member yet? For example, Lamb et al. 1 thermie 10 6. Clarity and Leadership for Environmental Awareness and Research at UC Davis, GWP* a better way of measuring methane and how it impacts global temperatures. Process model data or up-scaled flux observations can be used to prescribe emissions from natural wetlands, as well as methane uptake in dry soils (when soil acts as a sink). Methane (CH 4) is estimated to have a GWP of 27-30 over 100 years. Methane from oil & gas - Methane Tracker 2020 - Analysis - IEA chambers, diffusive methane emissions are quantified directly from the change in methane concentration over a short time series multiplied by the chamber volume/area ratio (Rolston, 1986). Measuring Natural Gas (MCF) - Overview and Accounting in MCF and natural gas production regions. CO2 is used as the base comparison gas for all other greenhouse gases, allowing for an easier estimation of the impact of all greenhouse gases in the atmosphere (including non-carbon-based gases, like nitrous oxide). (1999) found that compared to the a priori distributions of emissions, a posteriori emissions were reduced at high northern latitudes and increased at tropical and southern latitudes, a result obtained by many global inversions since (Bergamaschi et al., 2013; Bousquet et al., 2011; Bruhwiler et al., 2014; Houweling et al., 2014). A typical approach is to fly concentric closed flight paths at multiple altitudes around a source while continuously measuring methane concentrations, wind speed, and wind. Very high combustion efficiencies (>99.5%) for a single well completion flare; bottom-up inventories generally assume 98% efficiency. Adequate observational coverage in space and time is required to fully constrain inverse models at national or regional scales. Methane emissions from petroleum and natural gas supply chain sources reported in national inventories include sources from the wellhead to the point of use of the fuel, but they do not include emissions associated with end use (e.g., unburned methane from electricity power generation). . Do you like to eat? Additional methods can be employed that do not rely on calculating or estimating ventilation rates and can be applicable to open source areas (dry lots, pasture, manure storage areas, etc.). The resulting estimated emissions (posterior estimates) are in optimal agreement with both the priors and the observations, given. Improving Characterization of Anthropogenic Methane Emissions in the United States summarizes the current state of understanding of methane emissions sources and the measurement approaches and evaluates opportunities for methodological and inventory development improvements. Emissions from such sources are microbially driven or are subject to significant differences in equipment or operating practices, and as such, they are subjected to large temporal and spatial variability. In our next post on this topic, well explore in greater depth how leak rate and concentration measures differ, why theyre so incompatible, and the problems associated with using concentration measures for quantifying leak rates. For example, several validation studies using a backward Lagrangian stochastic inverse dispersion technique to measure emissions from livestock report errors of less than 20 percent, likely because these emissions are relatively uniform (e.g., Gao et al., 2010; McGinn et al., 2009; Ro et al., 2013). This page describes the calculations used to convert greenhouse gas emission numbers into different types of equivalent units. Tall towers (~300 m) are a useful way to understand regional greenhouse gas (GHG) variability because as the wind changes direction, it is possible to detect signals from surrounding nearby sources. Inverse techniques are diagnostic because they allow a look backward in time to understand trends in emissions. Some investigators have outfitted vehicles with the ability to measure concentrations at multiple heights above ground level, improving the characterization of the plume and the precision of the emission estimate. At many sites, however, it can be demonstrated that the intermediate cover areas emit the largest percentage of total emissions due to their large surface area and thinner cover soils (than final covers) (Spokas et al., 2015). If a valve is leaking, it is letting out a certain amount of gas every second, or hour. The study by Bergamaschi et al. Units are the yardstick by which we measure things: it does not make sense, for instance, to say that a persons height is 2. Another recent study also concluded that the capability of the sniffer method to adequately measure and rank methane emission rates among dairy cows is highly uncertain and requires further investigation into the sources of variation (Wu et al., 2017). Turner et al. The company has closely collaborated with numerous government and academic organizations. This leads naturally to using units of standard cubic feet per hour (SCFH) On the other hand, gas analyzers or sniffers, such as the SensIt, inhale a known volume of air, and determine the amount of methane mixed in with it, leading to the use of parts per million (PPM). Detailed guidelines for using the technique have been published by Berndt et al. For example, Henneberger et al. 2-3% of wells account for more than half of national unloading emissions. Activating CO2 to form methane is a potential strategy for energy decarbonization, but to activate CO2 typically requires high temperatures. Inverse models have proved to be an important tool, yet challenges to their usage remain, notably (1) the inability of the surface network to adequately reflect the full spatial variability of emissions, leading to multiple solutions that may significantly differ in spatial allocation of emissions and allocation of emissions among sources; and (2) the requirement that point measurements be accurately simulated with typically coarse-resolution transport models. Those data are then coupled with dispersion modeling to estimate an emission rate. Hellwing et al. Often limited to measurements from normal operations or where there are no safety concerns. Observations of methane column abundance from satellite platforms may significantly increase the spatial and temporal coverage of observational constraints (Jacob et al., 2016) on forward and inverse models used to estimate emissions. The app only works for flow rate measures; it doesnt allow conversion to concentration units, such as ppm or ppm-m. By this point in our tour of units, you know why: these units arent actually comparable, because they measure different things. Depending on the type of system present at a facility, the measurement techniques for estimating emissions from these sources will vary. Because U.S. emissions account. In contrast, biogenic coal-bed methane is generated by the breakdown of coal organic matter by methanogenic consortia of microorganisms at lower temperature, usually below 56C.
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