Researchers from the University of Southern California have used real-world satellite data to show that the adoption of electric vehicles (EVs) is having a direct impact on air pollution levels, reducing levels of nitrogen dioxide (NO₂), a major component of vehicle exhaust.
Despite the wildly fluctuating headwinds of American politics, more than 2.5 million EVs have been sold in California since 2010, according to the state’s governor Gavin Newsom, who made the announcement last week at the World Economic Forum in Davos, Switzerland.
This “shattered” the state’s clean cars goal of 1.5 million “zero-emission vehicles (ZEVs) on the road by 2025. Since the end of 2019, the cumulative sale of new ZEVs in California has grown by over 300 per cent driven by the state’s clean transportation policies and various incentives.
“While Washington now cedes the global clean vehicle market to China, California is ensuring American workers and manufacturers can compete and win in the industries that will define this century,” said Newsom, taking undisguised aim at US president Donald Trump.
Beyond infuriating Donald Trump and paving the way to curb future climate change, the uptake of EVs in California is starting to yield long sought-after real-world environmental benefits, which have been demonstrated for the first time using satellite data.
In a study published in The Lancet Planetary Health journal, researchers from the Keck School of Medicine at the University of Southern California (USC) have reported the first statistically significant decrease in nitrogen dioxide linked to zero-emission vehicles.
While there have been a number of studies promising improvements to air pollution levels associated with EV adoption, virtually all these studies have been based on projections of benefits rather than actual improvements.
Using measurements of nitrogen dioxide (NO2) air pollution from the Tropospheric Monitoring Instrument (TROPOMI) aboard the European Sentinel-5 Precursor (S5P) satellite, the researchers were able to show a reduction in NO2 levels corresponding to the uptake of EVs across California.
The researchers found that for every 200 ZEVs added in California between 2019 and 2023 there was a corresponding 1.1 per cent reduction in NO2 levels.
The research builds on a 2023 study by Keck researchers that suggested ZEV adoption was linked to lower air pollution levels, based on ground-level monitors, though at the time the results were not definitive.
The same research team has now been able to confirm the link thanks to high-resolution satellite data which detects atmospheric NO₂ – a pollutant released into the atmosphere by burning fossil fuels and which can trigger asthma attacks, cause bronchitis, and increase the risk of heart disease and stroke – by measuring how the gas absorbs and reflects sunlight.
“This immediate impact on air pollution is really important because it also has an immediate impact on health,” said Erika Garcia, PhD, MPH, assistant professor of population and public health sciences at the Keck School of Medicine and the study’s senior author.
“We know that traffic-related air pollution can harm respiratory and cardiovascular health over both the short and long term.”
California’s definition of zero-emission vehicles, and therefore the definition used in the new research, includes not only battery electric vehicles (BEVs) but also plug-in hybrid EVs (PHEVs) and fuel-cell EVs (FCEVs).
The research therefore not only shows the potential for further improvements to air pollution and public health with increased ZEV adoption, but the greater avenues for improvements when hybrid vehicles are phased out in favour of purely electric BEVs.
Despite the claims of carmakers around the globe, hybrids have repeatedly been shown to emit greater levels of pollution than promised. A September study showed that European PHEVs real-world emissions are five times higher than official tests suggest. A month later, the same researchers revealed that European PHEVs emit only 19 per cent less CO2 per kilometre on average than petrol and diesel cars.
So, even though BEVs account for the lion’s share of zero-emission vehicles on Californian roads – nearly 2 million compared to the 564,000 PHEVs and 18,500 FCEVs, according to the California Energy Commission – there remains significant room for improvement when hybrid vehicles are shown the door.
