Study unveils benefits of electric cars

A grey electric car connected to a charging station on campus.
The study found that for every additional 20 ZEVs per 1,000 people, there was a 3.2% reduction in the rate of asthma-related emergency visits. (Suejin Lim | Daily Trojan)

A team of researchers at the Keck School of Medicine documented the effect of adopting zero-emission vehicles in one of the first-ever studies in the field that reveals the association between ZEVs, air pollution and public health. 

ZEVs — primarily electric cars — have been presupposed as a pivotal part of the effort to ameliorate the climate crisis. However, not many studies have been done to bolster the widespread hypothesis.

The paper, published this February in Science of the Total Environment, analyzed the “natural experiment” in California as consumers’ adoption of ZEVs upticks rapidly. As ZEV adoption rose in a given zip code, local air pollution levels and emergency room visits dropped, the study found.

Erika García, an assistant professor of population and public health sciences at the Keck School of Medicine and the study’s lead author, has studied air pollution exposure in California for years. As the number of electric vehicles on the road has increased, she started wondering about the effect this would have on her field of study.

“As we are making this transition to electric vehicles, what are going to be the impacts on the air we breathe, and on the health of the community?” García asked.

Researchers at Keck obtained and analyzed four distinct datasets to study the effect of ZEV adoption. They first obtained data on ZEVs, including battery electric, plug-in hybrid and hydrogen fuel cell cars, from the California Department of Motor Vehicles and cataloged the registration information into different zip codes. 

The researchers also acquired data from the United States Environmental Protection Agency air monitoring sites on levels of nitrogen dioxide, a gaseous air pollutant that aggravates respiratory diseases, particularly asthma. They then calculated the percentage of adults in each zip code who held college degrees, a conventional indicator of the neighborhood’s socioeconomic status.

“What was really crucial is that … we are able to adjust for what’s called potential confounders,” said Sandrah Eckel, an associate professor of population and public health sciences at the Keck School of Medicine and the study’s senior author. “So, we wanted to control, for instance, socioeconomic status [of each zip code] to make sure that we weren’t finding spurious associations.”

Among all zip codes in the state, the average number of ZEVs in each area increased from 1.4 to 14.6 per 1,000 people from 2013 to 2019. The study found that for every additional 20 ZEVs per 1,000 people, there was a 3.2% reduction in the rate of asthma-related emergency visits and a suggestive drop in NO2 levels. 

The study also found that ZEV adoption was significantly lower in zip codes with lower levels of educational attainment. A zip code with 17% of its residents holding bachelor’s degrees had, on average, an annual increase of 0.7 ZEVs per 1,000 people, whereas zip codes with 47% of the population having a bachelor’s degree had an annual increase of 3.6 ZEVs per 1,000 people.

USC health sciences campus entrance
The study was limited, as analyzing the real-world benefits of ZEVs is more complicated than recording NO2 levels in different neighborhoods. (Noah Danesh | Daily Trojan)

This disparity in adoption rates of ZEVs in zip codes with varied socioeconomic status — which researchers dubbed the “adoption gap” — has underscored the challenge to enact environmental justice in low-resource communities, given that they have been disproportionately affected by tailpipe emission pollution.

“[The adoption gap] is particularly concerning,” García said. “Those communities that have residents that are of lower socioeconomic status might face additional barriers to accessing clean technologies, like electric vehicles, for a multitude of reasons.” 

Researchers recognize the limitations that the study faced. For one, analyzing the real-world benefits of ZEVs is much more complicated than merely recording NO2 levels in different neighborhoods. For instance, producing lithium-ion batteries for electric vehicles is more material-intensive than producing traditional combustion engines. As such, the extraction and processing of lithium from hard rock mines or underground brine reservoirs require a significant amount of energy coming from fossil fuels.

“A lifecycle analysis of technologies … is something that we do not consider here,” García said. “We only really look at the use or presumed use of electric vehicles, and we only really look at one type of air pollution, which is tied to traffic-related emissions.”

Even though electric vehicles could drastically reduce tailpipe emissions, the non-tailpipe emissions produced by ZEVs — like brake wear or tire wear, which also present health concerns — are left unanalyzed in the study. This is of particular concern warranting further research, García and her colleagues said, as electric vehicles produce more non-tailpipe emissions than their inner-combustion counterparts. 

“The study is great in that it is showing very early evidence that you could detect health effects of lower NO2,” said Rima Habre, an associate professor of population and public health sciences. “But we need to know a lot more about some of these other non-tailpipe emissions from electric vehicles, and how it sort of all plays out together.”

García said it was also difficult to disentangle the data from the impact of the coronavirus pandemic. 

“The pandemic impacted people and subsequently their health in many different ways,” García said. “If you are having asthma symptoms and you are worried, but maybe you are also worried about getting your child sick with COVID-19, [so] maybe you weren’t going to the emergency room.”

Researchers said they are content with their discoveries and hope the study leads to further policy changes that provide more resources to low-resource communities.

“We really do need to make sure that, with continued research, that there are appropriate policies and interventions put in place so that we can make sure that these benefits are equitably distributed across communities, especially those that are most vulnerable,” García said.