An increase in the use of electric passenger vehicles in the United States means reduced carbon emissions and cleaner air for most locations, according to research published today in Atmospheric Environment.
Scientists at Northwestern University took a number of variables into account to determine how mass adoption of battery-powered, light-duty vehicles would interplay with an increased demand for power generation. Using a computer model, they simulated how changing levels of renewable power generation sources would impact regional and seasonal air quality.
“The big question is: what would a large scale electrification of the transportation sector do to US air quality,” said Jordan Schnell, lead author and postdoctoral research fellow with the Ubben Program for Climate and Carbon Science at the Institute for Sustainability and Energy at Northwestern (ISEN).
Schnell, whose expertise is in chemistry-climate interactions, looked closely at two pollutants related to car and power emissions: ozone and particulate matter. He evaluated how their levels would change if electric vehicles were adopted at a rate of 25 percent or 75 percent. All this, while taking into consideration how the power supply for the vehicles would be generated. In particular, he looked at three possible power-generation scenarios for each geographic location: one reflecting the current mix of sources, a second doubling the level of current emission-free (wind, hydro, solar, and nuclear) sources, and a third with combustion (coal, oil, natural gas, and biomass) sources only.
“The big question is: what would a large scale electrification of the transportation sector do to US air quality," — Jordan Schnell, postdoctoral research fellow, Northwestern University
Across scenarios, “what we find is that the more cars you transition to electric vehicles, the better for summertime ozone,” explained Schnell, noting that ozone levels shrunk across the board in his simulations for warm weather months. “No matter how the power is generated, the more [combustion engine] cars you take off the road, the better the ozone quality.” However, due to a chemical interaction that occurs differently in warm weather with more sunlight versus cold weather and less sunlight, “in the wintertime, when ozone is already pretty low and it’s not really an issue for people, you actually do see a slight increase,” he noted.
Particulate matter, commonly referred to as haze, showed a different response to the adoption of electric vehicles. “You see that wintertime particulate matter goes down,” said Schnell. There are more variations in the summer response, based on location and how local power is generated. Locations with more coal-fired power show an increase on average and those with clean energy sources nearly eliminate the development of haze. “If you are in the Midwest, you can see some slight increases in particulate matter because the Midwest is largely reliant on coal. Now, if you were out in the Pacific Northwest and places in the Northeast that have essentially clean power, you see a decrease in particulate matter,” said Schnell.
Although not measured in the study, Schnell noted that in terms of carbon dioxide emissions, a transition to electric vehicles is a winner in all scenarios because power plants are more fuel efficient compared combustion engines.
The results of the study leave Schnell optimistic about a future where the majority, if not all, cars on the road are electric vehicles. “I think they are the poster child not only for climate change but also for air quality,” he said. At the same time, “we want to be careful about how we move forward. We want to make sure that not just the US but other places are advocating for them in a smart way because it’s not only the climate change issue but it’s also air pollution, and both have implications for human health.”
“In contrast to many of the scary climate science stories in the news,” said Daniel Horton, professor of climate science in the Department of Earth and Planetary Science and co-author of the study, “this work highlights an actionable solution that can help reduce both carbon emissions and air pollution – action on this front is a win-win for society.”
Schnell and his collaborators in the Department of Earth and Planetary Sciences at Northwestern and the Geophysical Fluid Dynamics Laboratory developed their models using open source data, so that they and other researchers can replicate the study across locations. They hope their research will inform decisions by municipalities and other stakeholders as initiatives to reduce carbon emissions and improve air quality move ahead.