DOI: 10.5281/zenodo.7672124
title: Gridded EPA U.S. Anthropogenic Methane Greenhouse Gas Inventory (gridded GHGI)

description: <strong><em>**** THE FOLLOWING DATA HAVE NOT BEEN PEER-REVIEWED ****</em></strong> <strong><em>*** This repository will be updated upon peer-review and final publication of the associated manuscript. ***</em></strong> <strong>About</strong> The gridded EPA U.S. anthropogenic methane greenhouse gas inventory (gridded GHGI) includes spatially and temporally resolved (gridded) maps of annual anthropogenic methane emissions (0.1°×0.1°) for the contiguous United States (CONUS). Total gridded methane emissions for each source sector are consistent with national annual U.S. anthropogenic methane emissions reported in the U.S. EPA <em>Inventory of U.S. Greenhouse Gas Emissions and Sinks</em> (U.S. GHGI). This repository accompanies the preprint manuscript <em>Maasakkers, et al., 2023, </em>which has been submitted as a non peer-reviewed preprint to EarthArXiv. This repository is an update to the gridded GHGI version 1, previously described in <em>Maasakkers, et al., (2016)</em> and currently available on the U.S. EPA website. The EPA website will be updated with version 2 of the gridded GHGI upon review and final publication of the manuscript. This repository contains two datasets: <strong>Gridded GHGI Data (main dataset; 2 file types). </strong>Gridded annual U.S. anthropogenic methane emissions for 2012-2018 for 26 source categories, hereafter called the gridded GHGI. This dataset is developed to be consistent with the national U.S. GHGI published in 2020 (<em>U.S. EPA , Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2020. U.S. Environmental Protection Agency, 2020, EPA 430-R-22-003, </em><em>https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks-1990-2018</em>) (hereafter called the U.S. GHGI). This gridded dataset represents an update to the original version 1 of the gridded GHGI from <em>Maasakkers, et al., (2016)</em>. The annual files contain one year of emissions per source category but include a time dimension to make them suitable (COARDS-compliant) for atmospheric models. This main dataset also includes monthly source-specific methane emission scaling factors for those select sources with strong interannual variability.<br> <br> a. Annual emission flux files containing individual variables for the 26 different source categories.<br> (dimensions: time x lat x lon; units: molec. CH­<sub>4</sub> cm<sup>-2</sup> s<sup>-1</sup>):<br> <em> - Gridded_GHGI_Methane_v2_YYYY.nc</em><br> <br> b. Monthly scaling factor files containing individual variables for the different source categories that have strong interannual variability. These scaling factors can be multiplied with the data in the annual emission files to get monthly methane emission fluxes for these select source categories.<br> (dimensions: time x lat x lon; units: dimensionless): <br> - <em>Gridded_GHGI_Methane_v2_Monthly_Scale_Factors_YYYY.nc</em><br> <strong>Gridded GHGI Express Extension (1 file type).</strong> Gridded annual U.S. anthropogenic methane emissions for 2012-2020 for 27 source categories (one additional source category compared to the main dataset above), hereafter called the express extension. This dataset is developed for total methane emissions to be consistent with the U.S. GHGI published in 2022 (<em>EPA (2022) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020. U.S. Environmental Protection Agency, EPA 430-R-22-003. https://www.epa.gov/ghgemissions/draft-inventory-us-greenhouse-gas-emissionsand-sinks-1990-2020)</em>. This dataset is *<strong>not</strong>* a full update to the main gridded GHGI dataset, and instead uses annual source-specific spatial patterns from 2012-2018 from the main dataset to quickly incorporate more recent national methane emission estimates. Emissions for years after 2018 follow the 2018 spatial patterns.<br> <br> a. Annual emission files<br> (dimensions: time x lat x lon; units: molec. CH­<sub>4</sub> cm<sup>-2</sup> s<sup>-1</sup>):<br> - <em>Express_Extension_Gridded_GHGI_Methane_v2_YYYY.nc</em> ---- <strong>Data Details:</strong> Annual gridded emissions files for both datasets (main gridded dataset and the express extension) include annual methane emission fluxes from the following sources: <em>Sources listed by name and IPCC/UNFCCC common reporting format (CRF) table categories.</em> <strong>Agriculture</strong> Enteric Fermentation (3A) Manure Management* (3B) Rice Cultivation* (3C) Field Burning of Agricultural Residues* (3F) <strong>Natural Gas Systems</strong> Exploration* (1B2b) Production* (1B2b) Transmission & Storage (1B2b) Processing (1B2b) Distribution (1B2b) Post-Meter (1B2b) (2022 express extension only) <strong>Petroleum Systems</strong> Exploration* (1B2a) Production* (1B2a) Transport* (1B2a) Refining* (1B2a) <strong>Waste</strong> Municipal Solid Waste (MSW) Landfills (5A1) Industrial Landfills (5A1) Domestic Wastewater Treatment & Discharge (5D) Industrial Wastewater Treatment & Discharge (5D) Composting (5B1) <strong>Coal Mines</strong> Underground Coal Mining (1B1a) Surface Coal Mining (1B1a) Abandoned Underground Coal Mines (1B1a) <strong>Other</strong> Stationary combustion* (1A) Mobile Combustion (1A) Abandoned Oil and Gas Wells (1B2a & 1B2b) Petrochemical Production (2B8) Ferroalloy Production (2C2) <strong>Additional Notes:</strong> ‘Grid_cell_area’ (dimensions: time x lat x lon, units: cm<sup>2</sup>) - this variable is included to help users convert the emission fluxes to emission mass totals. This variable includes a time dimension to make it suitable (COARDS-compliant) for atmospheric models. Monthly scale factors: Scale factors for the main dataset are published in a separate file for all sources listed above with an '*'. For the express extension, we recommend using the relative source-specific scale factors for years 2012-2018. Year 2018 scale factors can be used for manure management, rice cultivation, and field burning of agricultural residue emissions only. For other sources, monthly variability is too year-specific and should not be extrapolated to the express extension dataset for years after 2018. The gridded GHGI does not currently include emissions from the Land Use, Land Use Change, and Forestry (LULUCF) category of the national U.S. GHGI. Methane emissions from these sources include but are not limited to emissions from fires and flooded lands. Both datasets (main gridded dataset and express extension) were produced using source specific Jupyter Notebooks, which will be made available upon publication of the manuscript. ---- <strong>Frequently Asked Questions (FAQs):</strong> <strong>Q: How do both datasets (main gridded GHGI and express extension) relate to the U.S. National GHG Inventory (<em>Inventory of U.S. Greenhouse Gas Emissions and Sinks)?</em></strong> <strong><em>A: </em></strong>EPA develops an annual report, called the <em>Inventory of U.S. Greenhouse Gas Emissions and Sinks</em> (GHGI), that tracks U.S. greenhouse gas emissions and sinks by source, economic sector, and greenhouse gas going back to 1990 (called here the U.S. GHGI). The U.S. GHGI provides a comprehensive accounting of total greenhouse gas emissions for all human-made sources in the United States, including carbon dioxide removal from the atmosphere by “sinks,” (e.g., through the uptake of carbon and storage in forests, vegetation, and soils) from management of lands in their current use or as lands are converted to other uses. EPA has prepared the U.S. GHGI since the early 1990s and submits the report annually to the United Nations in accordance with the UN Framework Convention on Climate Change (UNFCCC). The emissions and removals in the U.S. GHGI are calculated using internationally accepted methods provided by the IPCC in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (2006 IPCC Guidelines) and where appropriate, its supplements and refinements. Data are reported in a common format, in line with the UNFCCC reporting guidelines. The U.S. GHGI is separate product to the EPA National Emissions Inventory (NEI). The gridded GHGI (main gridded dataset) was developed as a spatial representation of source-specific methane emissions reported in the 2020 U.S. GHGI (for years 2012-2018). In this product, the sum of gridded methane emissions for each source in each year will equal the total anthropogenic methane emissions from each source reported in the 2020 U.S. GHGI (excluding emissions from Alaska (AK), Hawaii (HI), and U.S. territories, which are not included in the gridded GHGI). As the U.S. GHGI is an annual report, some emission and sink estimates in the U.S. GHGI are recalculated and revised each year by the EPA to incorporate improved methods and/or data. The most common reason for recalculating U.S. greenhouse gas emission estimates is to update recent historical data. Changes in historical data are generally the result of changes in data supplied by other U.S. government agencies or organizations, as they continue to make refinements and improvements. These improvements are implemented consistently across the U.S. GHGI’s time series, as necessary, (i.e., 1990 to 2020) to ensure that the emissions trend is accurate. To reflect these changes, the express extension of the gridded GHGI is developed as an approximate representation of the spatial patterns of source-specific methane emissions reported in the 2022 U.S. GHGI report (for years 2012-2020). The fractional spatial patterns used to grid each source are the same as those derived from the main gridded dataset, but the sum of methane emissions from each source will equal those reported in the 2022 U.S. GHGI (excluding emissions from AK, HI, and U.S. territories, which are not included in the gridded GHGI). Users are directed to the 2020 and 2022 EPA National GHGI Reports for more specific information about major methodological differences between the two national inventory versions. <strong>Q: How does the EPA National U.S. GHGI compare to the EPA GHG Reporting Program?</strong> <strong>A:</strong> “EPA collects greenhouse gas emissions data from individual facilities and suppliers of certain fossil fuels and industrial gases through its Greenhouse Gas Reporting Program (GHGRP), which is complementary to the U.S. Inventory. The GHGRP applies to direct greenhouse gas emitters, fossil fuel suppliers, industrial gas suppliers, and facilities that inject carbon dioxide (CO<sub>2</sub>) underground for sequestration or other reasons and requires reporting by over 8,000 sources or suppliers in 41 industrial categories. Annual reporting is at the facility level, except for certain suppliers of fossil fuels and industrial greenhouse gases. In general, the threshold for reporting is 25,000 metric tons or more of CO<sub>2</sub> equivalent per year. Facilities in most source categories subject to GHGRP began reporting for the 2010 reporting year while additional types of industrial operations began reporting for reporting year 2011. Methodologies used in EPA’s GHGRP are consistent with the <em>2006 IPCC Guidelines</em>. While the GHGRP does not provide full coverage of total annual U.S. greenhouse gas emissions and sinks (e.g., the GHGRP excludes emissions from the agricultural, land use, and forestry sectors), it is an important input to the calculations of national-level emissions in this Inventory. The GHGRP dataset provides not only annual emissions information, but also other annual information such as activity data and emission factors that can improve and refine national emission estimates over time.” <em>Box ES-1 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2021.</em> <strong>Q: Does the sum of source-specific gridded emissions equal the total national emissions reported in the EPA U.S. GHGI?</strong> <strong>A: </strong>Gridded GHGI emissions currently include emissions from the contiguous U.S. (CONUS). The CONUS emission totals in the gridded GHGI are consistent with the U.S. GHGI, except for emissions from Alaska, Hawaii, or U.S. Territories, which are not included in the gridded product. Both the main gridded GHGI dataset and the express extension include all anthropogenic methane sources included in the U.S. GHGI, except for methane emissions from LULUCF categories. <strong>Q: Do the gridded GHGI dataset and express extension account for all sources of methane (anthropogenic + natural) in the contiguous U.S.?</strong> <strong>A:</strong> No. These datasets do not include natural methane emission sources. In addition, neither the main gridded GHGI dataset nor the express extension include emissions for the LULUCF categories, which are included in the U.S. GHGI. For these emission sources, users can supplement the gridded data with external global gridded data products. <strong>Q: Should I use the main gridded dataset or express extension?</strong> <strong>A: </strong>For applications that require comparisons to emissions from the 2020 U.S. GHGI Report, we recommend using the main gridded GHGI dataset. These data are the most accurate representation of the geographic distribution of methane emissions from the 2020 U.S. GHGI. For modeling analyses or comparisons to data collected in more recent years, or for direct comparisons to the 2022 U.S. GHGI, we recommend using the express extension dataset. Regardless of application, users *<strong>should not</strong>* combine emissions data from the main gridded dataset with the express extension. The 2020 and 2022 U.S. GHGI Reports are separate inventories of historical annual U.S. methane emissions and therefore using emissions from both the main gridded dataset and express extension would not correspond to total emissions from either U.S. GHGI Report and could result misinterpretations or step changes in the magnitude of emissions between the two gridded datasets. For inverse modeling applications that require total methane emissions (anthropogenic + natural sources), users are directed to external global emission databases for sources not included in the gridded GHGI<strong>.</strong> <strong>Q: Why was the express extension dataset developed?</strong> <strong>A:</strong> The express dataset was developed as an extension to the main gridded GHGI and represents approximate spatial patterns of methane emissions from the 2022 U.S. GHGI Report. This “express extension” enables comparisons to more recent emission estimates from atmospheric observations. EPA has made several improvements to the U.S. GHGI since the publication of the 2020 Report, which impact methane emission estimates across the (extended) time series. To incorporate some of these recent improvements, this express dataset extends the same gridding methodology from main gridded GHGI dataset (spatial patterns held constant after 2018), but scales total CONUS emissions to those consistent with the 2022 U.S. GHGI. <strong>Q: Which monthly scale factors should I use with the express extension dataset?</strong> <strong>A:</strong> Monthly scale factors were developed for the main gridded GHGI dataset, for sources with strong interannual variability. Separate temporal monthly scale factors were not developed for the express extension dataset. For years 2012-2018, the source-specific monthly scaling factors can be applied to the corresponding source emission fluxes in the express extension. For years after 2018, monthly scaling factors should only be applied to manure management, rice cultivation, and field burning of agricultural residue emissions. Variability in these sources is largely driven by seasonal conditions, where variability in the year 2018 can be used to approximate seasonal variability in later years. In contrast, monthly variability in other emission sources is too year-specific to be extended to the express dataset beyond 2018. <strong>Q: What units are methane emissions reported in?</strong> <strong>A:</strong> The annual files of the main gridded product and the express extension both include methane emissions as fluxes, in units of molecules CH<sub>4</sub>/cm<sup>2</sup>/s. To convert annual data from emission fluxes to total annual emissions (Teragrams/year), use the following conversion: \(\text{Methane emissions [Tg per year]} = {\text{Methane flux } [molec. cm^{-2} s^{-1}] * \text{Conversion factor } }\) \(\text{Conversion factor} = {1 \over 6.022x10^{23}} \text{ [mole per molec.]} *{16.04x10^{-12} \text{ [Tg per mole]}} * {86400 \text{ [s per day]}} *{\text{ [days per year]}} *{\text{ grid cell area } [cm^2]} \) The number of days per year depends on whether the given year is a leap year. <br> A gridded map (0.1° x 0.1°) of grid cell areas is available in each annual emission files (in units of cm<sup>2</sup>).