DOI: 10.5281/zenodo.16782734
title: Gridded U.S. Anthropogenic Methane Greenhouse Gas Inventory (gridded GHGI)

description: **** THE FOLLOWING DATA HAVE NOT BEEN PEER-REVIEWED ****

*** This repository will be updated upon peer-review and final publication of an associated manuscript.  For questions and answers about previous versions of this dataset, please visit previously published Zenodo records: https://zenodo.org/records/8367082 

***

About

The gridded 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 Inventory of U.S. Greenhouse Gas Emissions and Sinks (U.S. GHGI).

This repository is an update to the gridded GHGI version 2, previously described in Maasakkers, et al., 2023 and available at: https://zenodo.org/records/8367082

This work was led by RTI International, funded by contract number: 68HERH19D0030/68HERH24F0030.

This repository contains the follow data:

Gridded GHGI v3 (2 file types). Gridded annual U.S. anthropogenic methane emissions for 2012-2022 for 34 source categories. This dataset is developed to be consistent with the national U.S. GHGI published in April 2024 (U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2022. U.S. Environmental Protection Agency, 2024, EPA 430-R-24-004, https://www.epa.gov/system/files/documents/2024-04/us-ghg-inventory-2024-main-text_04-18-2024.pdf).This dataset includes 2 file types: a. Annual methane emission fluxes for 34 inventory source categories. Files contain one year of emissions per source category and include a time dimension variable to make the data suitable (COARDS-compliant) for atmospheric models.(Dimensions: longitude x latitude x time; units: molecules CH­4 cm-2 s-1):     - Gridded_GHGI_Methane_v3_YYYY.ncb. Monthly emission scaling factors for inventory source categories with interannual variability (see 'Data Details' below). To use these factors to calculate absolute monthly methane emission fluxes, multiply the scaling factors for each relevant source category by the corresponding emission fluxes in the annual flux files. (Dimensions: longitude x latitude x month; units: dimensionless):      - Gridded_GHGI_Methane_v3_Monthly_Scale_Factors_YYYY.nc
description: Data Details:

Annual gridded files include annual methane emission fluxes from the following inventory source categories:

Sources are listed by name and category, which are from the IPCC/UNFCCC common reporting format (CRF) tables. Sources with an '*' are also reported with monthly emission scale factors. 

Agriculture



Enteric Fermentation* (3A)

Manure Management* (3B)

Rice Cultivation* (3C)

Field Burning of Agricultural Residues* (3F)


Natural Gas Systems



Exploration* (1B2b)

Production* (1B2b)

Transmission & Storage (1B2b)

Processing (1B2b)

Distribution (1B2b)

Post-Meter (1B2b)


Petroleum Systems



Exploration* (1B2a)

Production* (1B2a)

Transport* (1B2a)

Refining* (1B2a)


Waste



Municipal Solid Waste (MSW) Landfills (5A1)

Industrial Landfills (5A1)

Domestic Wastewater Treatment & Discharge (5D)

Industrial Wastewater Treatment & Discharge (5D)

Composting (5B1)

Anaerobic Digestion at Biogas Facilities (5B2)


Coal Mines



Underground Coal Mining (1B1a)

Surface Coal Mining (1B1a)

Abandoned Underground Coal Mines (1B1a)


Land Use, Land Use Change, and Forestry



Fires on Forest Land Remaining Forest Land* (4A1 & 4A2)

Fires on Grassland Remaining Grassland* (4C1 & 4C2)

Wetlands Remaining Wetlands (4D1)

Land Converted to Wetlands (4D2)


Other



Stationary Combustion* (1A)

Mobile Combustion (1A)

Abandoned Oil and Gas Wells (1B2a & 1B2b)

Carbide Production (2B5)

Petrochemical Production (2B8)

Iron and Steel Production (2C1)

Ferroalloy Production (2C2)


Additional Variables:



'Grid_cell_area' (dimensions: longitude x latitude x time, units: cm2) - this variable is included to help users convert from methane emission flux (molecules CH­4 cm-2 s-1) to total mass (metric tons CH4). This variable includes a time dimension to make it suitable (COARDS-compliant) for atmospheric models.


Additional Notes



Monthly scale factors



To use these factors to calculate monthly methane emission fluxes, multiply the scaling factors for each relevant source category by the corresponding emission fluxes in the annual flux files. The scaling factors have dimensionless units



Variable name changes between v3 and v2 (not including the express extension). The same variable name changes apply to both the annual emission flux files and the monthly scaling factors:



 v3: 1A mobile combustion; v2: 1A Combustion Mobile

v3: 1A stationary combustion; v2: 1A Combustion Stationary

v3: 1B1a coal mining surface; v2: 1B1a Surface Coal

v3: 1B1a coal mining underground; v2: 1B1a Underground Coal

v3: 1B1a abandoned coal; v2: 1B1a Abandoned Coal

v3: 1B2ab abandoned og wells; v2: 1B2ab Abandoned Oil Gas

v3: 1B2ai petroleum exploration; v2: 1B2a Petroleum Systems Exploration

v3: 1B2aii petroleum production; v2: 1B2a Petroleum Systems Production

v3: 1B2aiii petroleum transport; v2: 1B2a Petroleum Systems Transport

v3: 1B2aiv petroleum refining; v2: 1B2a Petroleum Systems Refining

v3: 1B2bi ng exploration; v2: 1B2b Natural Gas Exploration

v3: 1B2bii ng production; v2: 1B2b Natural Gas Production

v3: 1B2biii ng processing; v2: 1B2b Natural Gas Processing

v3: 1B2biv ng transmission storage; v2: 1B2b Natural Gas TransmissionStorage

v3: 1B2bv ng distribution; v2: 1B2b Natural Gas Distribution

v3: 1B2bvi1 ng postmeter; v2: n/a

v3: 2C2 ferroalloy; v2: 2C2 Industry Ferroalloy

v3: 2B8 petrochemicals; v2: 2B8 Industry Petrochemical

v3: 2C1 iron and steel; v2: n/a

v3: 2B5 carbide; v2: n/a

v3: 3A enteric fermentation; v2: 3A Enteric Fermentation

v3: 3B manure management; v2: 3B Manure Management

v3: 3C rice cultivation; v2: 3C Rice Cultivation

v3: 3F4 fbar; v2: 3F Field Burning

v3: 4A1 4A2 Forest land remaining forest land; v2: n/a

v3: 4C1 4C2 Grassland remaining grassland; v2: n/a

v3: 4D1 wetlands remaining wetlands; v2: n/a

v3: 4D2 land converted to wetlands; v2: n/a

v3: 5A industrial landfills; v2: 5A1 Landfills Industrial

v3: 5A msw landfills; v2: 5A1 Landfills MSW

v3: 5B1 composting; v2: 5B1 Composting

v3: 5B2 anaerobic digestion; v2: n/a

v3: 5D1 domestic wastewater; v2: 5D Wastewater Treatment Domestic

v3: 5D2 industrial wastewater; v2: 5D Wastewater Treatment Industrial



Multiple updates have led to changes in the gridded methane emission fluxes in the gridded GHGI v3, compared to v2 (published in 2023). Major differences include:



The gridded GHGI v3 now includes gridded methane emission fluxes for Land Use, Land Use Change, and Forestry sources, as well as three new industry and waste sources.

Data and methodological updates to the National GHGI have led to updated gridded GHGI estimates. These updates result in increases in national emission estimates for many sources across the 2012-2018 time period compared to in v2, including for natural gas and petroleum systems, wastewater treatment, and select agricultural sources. However, not all sources have higher emissions in the 1990-2022 GHGI, for example, some natural gas transmission and storage emissions have been revised downward. For more information on the National GHGI and methodological updates, visit this page.

The spatial allocation approach, as described in Maasakkers et al., 2023 has been updated in v3 to include source-specific emissions from the State 1990-2022 GHGI. Therefore, when aggregated, gridded methane emissions for each source and year will be consistent with emission from the 1990-2022 State GHGI at the state-level, as well as with the 1990-2022 National GHGI when aggregated across the country. Previously, the gridded GHGI v2 was not consistent with the State GHGI. As a result, there are noticeable state-by-state changes in gridded methane emissions between v2 and v3. These differences are greatest for sources where the State GHGI methodology differed from the state allocation method that was used in v2 of the gridded GHGI. For example, stationary combustion methane emissions are generally higher in northeastern states in 2015 and 2016 in v3 than in v2 because a larger fraction of national emissions were estimated to occur in those states in the 1990-2022 State GHGI as compared to the national-to-state allocation method that had previously been used in v2 of the gridded GHGI.

Where available, all proxy data underlying the gridded GHGI have been updated to more recently published versions. For example, more recent oil and natural gas well-level information is available from the proprietary Enverus dataset.

The coding system used to allocate emissions for the gridded GHGI has been updated from a series of Jupyter notebooks to a system of python scripts. These scripts standardize the gridding procedure and improve gridding efficiencies. As a result, the approach for gridding of some sources has slightly changed. For example, for livestock emissions, these data in v3 are allocated exclusively to grid cells whose center falls within a county border, rather than partially allocated to those that touch multiple county borders (i.e., have area both within and outside). This results in some noticeable differences in the methane emission fluxes between v2 and v3 for these sources around county borders.

For other questions about methodological changes between v2 and v3, please reach out to the data authors.



This code used to develop this dataset is available on GitHub. Select input data may be available upon request.
description: Frequently Asked Questions (FAQs):

Q: Has this dataset been peer-reviewed?

A: No. This dataset has not been peer-reviewed. Previous versions of the gridded methane dataset have been reviewed as part of the Maasakkers et al., 2023 manuscript. 

Q: How does v3 of the gridded methane GHGI differ from v2?

A: Version 3 of the gridded methane GHGI has been developed by RTI International, with support from external collaborators. Compared to v2, version 3 includes annual gridded methane fluxes for more source categories (34 vs. 26), for two additional years (2021 and 2022), and corresponds to a more recent version of the U.S. GHGI (1990-2022 Inventory Report). In addition, gridded emissions in v3 were developed to sum to both the state and national inventory reports whereas gridded emission in v2 were only developed to sum to national totals. As the entire timeseries of the GHGI is updated upon each annual report publication, users should not combine emissions from v2 and v3.

Q: Should I use v2 or v3?

A: Users are recommended to use v3 of the gridded methane dataset, as it reflects a more recent version of the U.S. GHG Inventory. However, v3 has not been peer-reviewed and therefore, there are likely some applications where it may be better to continue using v2.

Q: How does this dataset relate to the U.S. National GHG Inventory (Inventory of U.S. Greenhouse Gas Emissions and Sinks)?

A: The Inventory of U.S. Greenhouse Gas Emissions and Sinks (GHGI) 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. Corresponding state-level inventory reports were published in 2022, 2023, and 2024.

The gridded GHGI includes annual emission fluxes for 34 individual inventory emission source categories, including those from agriculture, petroleum and natural gas systems, coal mining, LULUCF, and waste. Gridded methane emissions data are generated by allocating state annual U.S. GHGI methane emissions from individual source categories to a 0.1° x 0.1° grid using a series of spatial and temporal 'proxy' datasets at the county and grid levels. Where possible, proxy data are the same data used to develop the U.S. GHGI so that the gridded emissions can be, as closely as possible, a spatial and temporal representation of the state-level U.S. GHGI. In this product, the sum of annual gridded methane emissions for each source will equal the total anthropogenic methane emissions from each corresponding source as reported in the 2022 U.S. GHGI (except for emissions from Alaska (AK), Hawaii (HI), and U.S. territories, which are not included in the gridded GHGI).

Gridded methane emission products can be used by researchers for a better comparison of the national U.S. GHGI with (regional and local) observations of atmospheric methane.

Q: Does the sum of source-specific gridded emissions equal the total national emissions reported in the U.S. GHGI?

A: The gridded GHGI includes anthropogenic methane emissions from the contiguous U.S. (CONUS). Total CONUS emissions in the gridded GHGI are consistent with the U.S. GHGI. The gridded product does not include emissions from Alaska, Hawaii, or U.S. Territories. The v3 gridded GHGI includes all anthropogenic methane sources included in the U.S. GHGI.

Q: Does the gridded GHGI account for all sources of methane (anthropogenic + natural) in the contiguous U.S.?

A: No. The gridded GHGI does not include natural methane emission sources. For these emission sources, users can supplement the gridded data with external global gridded data products. Users should, however, also be aware of potential overlap in emissions from the GHGI and other emission products. For example, the LULUCF source categories (fires and wetlands) in the GHGI include emission estimates from these sources that occur on managed land. External emission inventories that include wetland and fire emissions may not make these same distinctions between emissions occuring on managed vs. unmanaged land. For more information on the GHGI LULUCF sources, see the GHGI methodology report.   

Q: What units are methane emissions reported in?

A: The annual files include methane emission fluxes, in units of molecules CH4/cm2/s. To convert annual data from emission fluxes to total annual emissions (Teragrams/year), use the following conversion:

Methane emissions [Tg per year] = Methane flux [molec. cm^-2 s^-1] * Conversion factor 

Conversion factor = 1/6.022x10^23 [mole per molec.] * 16.04x10^-12 [Tg per mole] * 86400 [s per day] * [days per year] * grid cell area [cm^2]

The number of days per year depends on whether the given year is a leap year. The one exception is for livestock emissions (manure management and enteric fermentation) where total mass emissions for all years need to be calculated assuming 365 days per year.

A map (0.1° x 0.1°) of grid cell areas is available in each annual emission file to assist with this conversion (in units of cm2).