US-REGEN Documentation

Air Quality

US-REGEN estimates changes in economy-wide criteria air pollutant (CAP) emissions based on the EPA'a National Emissions Inventory.[1] The following CAPs and precursors for ozone and particulate matter (PM) are modeled in US-REGEN:

  • Ammonia (NH3)
  • Carbon monoxide (CO)
  • Nitrogen oxides (NOx)
  • Primary particulate matter less than 10 microns (PM10)
  • Primary particulate matter less than 2.5 microns (PM2.5)
  • Sulfur dioxide (SO2)
  • Volatile organic compounds (VOCs)

Figure 1 illustrates how criteria air pollutant emissions are represented in US-REGEN. The model integrates EPA Modeling Platform 2016v2 data as base year data; maps data into service, fuel use, and end-use categories; and derives emissions rate index values for future projection periods. Based on model outputs, future CAP emissions are estimated by scaling base year emissions associated with each sector/service and fuel/fuel use categories with indexed growth rates of emission drivers.

Figure 1: US-REGEN representation of criteria air pollutants

REGEN establishes a link between National Emissions Inventory (NEI) emissions data as REGEN input using source classification codes (SCCs).[2] SCC codes indicate the sector, activities, and fuel use involved with the source of emissions. In US-REGEN, each data record from NEI is paired with an SCC sector/activity code for emissions source and an SCC fuel code, which are assigned if the source is related to fuel combustion or use. For NEI point source data, additional mapping is implemented using NAICS codes.

US-REGEN treats emissions associated with fuel use and non-fuel use separately. Future year emissions for non-fuel use are the product of base year non-fuel use emissions and indexed growth path for service demand. Future year emissions associated with fuel use consider both indexed growth rate of emissions drivers for fuel use and indexed decline of emissions rates. The former is derived from regional delivered fuel demands from the end-use sectors, and the total supply and demand of fuels from the upstream fuel production sector. The latter indexed decline of emission rates are inputs from modeling platform 2016v2 from on-road, non-road/light-duty vehicles, marine, and rail emission rates.

For additional detail on US-REGEN CAP emissions and air quality modeling, see Bistline, et al. (2022)open in new window.[3]

  1. https://www.epa.gov/air-emissions-modeling/2016v2-platformopen in new window ↩︎

  2. https://www.epa.gov/air-emissions-inventories/national-emissions-inventory-neiopen in new window ↩︎

  3. Bistline, et al. (2022). Economy-Wide Evaluation of CO2 and Air Quality Impacts of Electrification in the United States. Nature Communications, 13: 6693. ↩︎

Last updated: May 23, 2025