Air Quality Impacts from the Electrification of Light-duty Passenger Vehicles in the United States

A central strategy in achieving greenhouse gas mitigation targets is the transition from conventional gasoline- and diesel-powered vehicles to an electric fleet. However, due to complex emission sources and nonlinear chemistry, it is unclear how such a shift might impact air quality. Here we apply a high-resolution ( 0.5°) version of the new-generation NOAA GFDL Atmospheric Model, version 4 (GFDL AM4) to investigate the impact on U.S. air quality from an aggressive conversion of internal combustion vehicles to battery-powered electric vehicles (EVs). We examine a suite of scenarios designed to quantify the effect of both the magnitude of EV market penetration and the source of electricity generation used to power them. We find that summer surface ozone (O₃) decreases in most locations due to widespread reductions of traffic NO_x emissions. Summer fine particulate matter (PM_2.5) decreases slightly over the western U.S. but increases on average over the eastern U.S. due to increased sulfate, largely a product of coal-fired power generation. The results are reversed for winter: O₃ increases due to reduced loss via traffic NO_x and PM_2.5 decreases since larger nitrate reductions offset increases in sulfate. The largest magnitude changes are simulated at the extremes of the probability distribution. Increasing the fraction of electricity generated by "emission-free" sources further decreases summer O₃ and largely eliminates the increases in summer PM_2.5. Ultimately, the number of conventional vehicles replaced by EVs has a larger effect on O₃ than PM_2.5, while the source of the electricity for those EVs exhibit greater control on PM_2.5.