Overview

Data Sources #

The primary data sources used are the National Emissions Inventory (NEI) and the U.S. Energy Information Administration’s State Energy Data System (EIA SEDS). The NEI, administered by the Environmental Protection Agency (EPA), provides comprehensive estimates of air emissions for criteria pollutants, their precursors, and hazardous air pollutants. These estimates are compiled from information provided by State, Local, and Tribal agencies

The EIA SEDS dataset is an estimate of energy production and fuel consumption by state, economic sector, and fuel type. The EIA SEDS dataset provides historical as well as forecasted estimates.

The NEI dataset is updated every three years, does not include CO₂ emissions for all sectors, and may contain missing or erroneous data. To address these gaps, we incorporate data from many other datasets, which are described in the following sections. The EIA SEDS dataset is used to fill in missing information both temporally and spatially, where applicable. Fuel consumption data, categorized by fuel type and state, is used to interpolate NEI data between reporting years for certain sectors where more temporally granular estimates are not available.

For large point sources, we incorporate self-reported emissions as required by EPA regulations. Similarly, federal government data for mobile sources aid in supporting inventory accuracy and monitoring mobile activity.

Spatial Scale #

Hexagons #

The hexagons depict a gridded representation of emissions from the sources selected by the user. The color of the hexagon indicates the quantity of emissions occurring within the hexagon. Within each hexagon, emissions estimates are aggregated to provide an overall estimate. The area of the hexagons will vary depending on the viewer’s screen dimensions. The highest resolution of hexagons available for viewing are approximately 0.7 km² in area.

Census #

The highest resolution available in this view are census block groups. As in the hexagons view, color of the census group block in the map indicates the quantity of emissions within the selected group block. Census block groups are defined by the US census, are designed to be relatively homogenous with regards to key demographic characteristics and are uniquely numbered subdivisions within US counties. As of 2022, there are 239,780 census block groups in the United States.

Sectors #

Direct Emissions #

Direct greenhouse gas emissions, also referred to as Scope 1 emissions, are from the combustion of fuels and from industrial processes such as cement production. We provide estimates of direct CO₂ emissions, categorized into the following source sectors and sub-sectors:

  • Airports
  • Commercial, Residential and Industrial Buildings
    • Commercial Buildings
      • Commercial Buildings (Non-Point)
      • Agricultural Equipment
    • Industrial Buildings
      • Industrial Facilities (Stationary Point)
      • Industrial Buildings (Non-Point)
      • Oil & Gas
    • Residential Buildings
  • Mobile Equipment
  • Other
    • Railroad
    • Commercial Marine Vessels
  • Power Plants
  • Vehicles

Emissions from Electricity Use #

Emissions from electricity use, also referred to as Scope 2 emissions, are indirect greenhouse gas emissions associated with consumed electricity, estimated at the location of electricity consumption, rather than at the location of electricity production (e.g., at the location of a power plant).

Data Integrity #

Crosswalk puts the ingested data, intermediate model outputs, and final estimates of emissions through an extensive QA/QC processes to ensure the data are complete and do not exhibit any unexplained anomalies or unexplained outliers. Crosswalk also continuously searches for and incorporates new sources of data to test against and to improve the accuracy of estimates. Manual corrections are made to the geocoordinates of certain facilities by checking against Google Earth and other asset mapping data tools.

Emission Factors & Temporal Interpolation #

For some sources of emissions, such as emissions from large industrial facilities at fixed locations, Crosswalk uses reported values of emissions directly, and therefore does not need to apply emission factors or perform additional steps to generate estimates. For source sectors where emission factors are applied, they are compiled from various sources including the EPA and Intergovernmental Panel on Climate Change (IPCC). In sectors where NEI is the main data source, Crosswalk performs interpolation to generate annual emissions estimates for years in which the NEI values are unavailable. For these sectors, the State Energy Data System (SEDS) is used to calculate fuel consumption ratios. SEDS fuel consumption data is broken out into identifying codes which describe the economic sector, fuel type, and consumption unit. These codes are matched up with the Crosswalk emissions sectors, and the ratio of year over year fuel consumption is use to interpolate values for years for which there is not NEI data.