Researchers from Northwestern University and Princeton University have explored the impact on US air quality from an aggressive conversion of internal combustion vehicles to battery-powered electric vehicles (EVs). In a paper published in the journal Atmospheric Environment, they report on the findings from 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.
The exponentially increasing global market share of EVs has prompted research on their efficacy in reducing greenhouse gases, but comparatively little effort has focused on their impact on air quality. This despite evidence that suggests air pollution impacts from the transportation sector exceed those from greenhouse gases.
… The impact on air quality from the adoption of EVs can vary substantially between regions depending on existing transportation type and density, proximity to and type of power generation, and the region’s chemical regime (e.g., NOx-vs.VOC-limited for O3, NH3-rich vs. NH3-poor for PM). For example, states in the western US (WUS) generally produce a larger fraction of their electricity from renewable and/or “emission-free” sources (i.e., solar, wind, hydroelectric, and nuclear) as compared to the eastern US (EUS), where the electricity market is dominated by pollutant and precursor emitting combustion sources (i.e., coal, oil, natural gas, and biomass).
Most studies that have examined the impact of EVs report only changes in the total emissions associated with their adoption, but do not consider their spatial or temporal variation. … Thus to fully account for the complexity of changes to air pollution chemistry, emission changes should be used to drive a chemical transport model (CTM).—Schnell et al.
In the study, the researchers applied a prototype version of the new-generation NOAA GFDL global Atmospheric Model, version 4,for their simulations.
To fully account for the complexity of changes to air pollution chemistry, the researchers took multiple variables into consideration:
Potential electric vehicles adoption rates;
Generation of electric vehicle power supply, including the current combustion-dominant mix, combustion-only sources and enhanced emission-free renewables;
Geographical locations; and
Seasons and times of day.
Among the findings:
Summer surface ozone (O3) decreases in most locations due to widespread reductions of traffic NOx emissions.
Summer fine particulate matter (PM2.5) increases on average and largest in areas with increased coal-fired power generation demands.
Winter O3 increases due to reduced loss via traffic NOx.
Winter while PM2.5decreases since larger ammonium nitrate reductions offset increases in ammonium sulfate.
Increasing the fraction of vehicles converted to EVs further decreases summer O3, while increasing the fraction of electricity generated by “emission-free” sources largely eliminates the increases in summer PM2.5 at high EV adoption fractions. Ultimately, the number of conventional vehicles replaced by EVs has a larger effect on O3 than PM2.5, while the source of the electricity for those EVs exhibit greater control on PM2.5.—Schnell et al.
Air quality changes binned at each 10th percentile and averaged over the WUS (left column, west of 100°W) and EUS (right column, east of 100°W) for each EV adoption scenario (colors) shown for (a, b) O3, (c, d) PM2.5 for April-September, (e, f) PM2.5 for October-March, (g, h) (NH4)2SO4, and (i, j) NH4NO3. Schnell et al.
Across scenarios, we found the more cars that transitioned to electric power, the better for summertime ozone levels. No matter how the power is generated, the more combustion cars you take off the road, the better the ozone quality.—first author Jordan Schnell, a postdoc with the Ubben Program for Climate and Carbon Science in the Institute for Sustainability and Energy at Northwestern
Particulate matter decreased in the wintertime but showed greater variation based on location and how the power was generated. Locations with more coal-fired power in their energy mix experienced an increase in PM during the summer. Locations with clean energy sources, however, saw reductions.
We found that in the Midwest, the increased power demands of EV charging in our current energy mix could cause slight increases in summer particulate matter due to the reliance on coal-fired power generation. However, if we transition more of the Midwest’s power generation to renewables, particulate matter pollution is substantially reduced. In the Pacific Northwester or Northeast, where there is already more clean power available, EV adoption—even with the current energy mix—will decrease particulate matter pollution.—Jordan Schnell
The research was supported by the Ubben Program for Carbon and Climate Science and the National Science Foundation (grant number CBET-1848683).
Jordan L. Schnell, Vaishali Naik, Larry W. Horowitz, Fabien Paulot, Paul Ginoux, Ming Zhao, Daniel E. Horton (2019) “Air quality impacts from the electrification of light-duty passenger vehicles in the United States,” Atmospheric Environment, Volume 208, Pages 95-102 doi: 10.1016/j.atmosenv.2019.04.003