Development of the United States GReenhouse Gas and Air Pollutants Emissions System (GRA²PES)

In the U.S., emissions of greenhouse gases and air pollutants are often developed independently. Here, we describe the GReenhouse gas And Air Pollutants Emissions System (GRA²PES), which provides gridded emissions of fossil-fuel carbon dioxide (ffCO₂) and 93 air quality (AQ) species for 17 combustion and non-combustion sectors at 4 km × 4 km spatial resolution across the contiguous US. We find that the AQ emissions most spatially correlated with ffCO₂ are nitrogen oxides (NO_x, ρ = 0.67), followed by sulfur dioxide (SO₂, ρ = 0.51), carbon monoxide (CO, ρ = 0.44), and fine particulate matter (PM_2.5, ρ = 0.38). We evaluate GRA²PES ffCO₂ emissions with an ensemble of publicly available regional and global inventories at national (Normalized Mean Bias (NMB) = +1.4%), state (NMB = +1.5%, R² = 0.98), and urban (NMB = +11.5%, R² = 0.97) scales. Nationally, the differences of publicly available inventories from the ensemble average range from −10.0% to +5.7%, and consistency diverges at state and urban scales. We simulate GRA²PES ffCO₂ in a particle dispersion model and compare to measurements of radiocarbon (¹⁴C)-derived ffCO₂ collected in Los Angeles (August 2021), with results suggesting that GRA²PES ffCO₂ may be low by 19% for this city, but well within model-observation differences for other publicly available inventories (−43% to +94%). GRA²PES AQ/ffCO₂ ratios converted to concentration space generally agree with field observations (NMB = +4%, log R² = 0.90). Lastly, we present a method by which to utilize GRA²PES to derive AQ emission fluxes from ffCO₂ emissions.