When California neighborhoods increased their number of zero-emissions vehicles (ZEV) between 2019 and 2023, they also experienced a reduction in air pollution. For every 200 vehicles added, nitrogen dioxide (NO₂) levels dropped 1.1%. The results, obtained from a new analysis based on statewide satellite data, are among the first to confirm the environmental health benefits of ZEVs, which include fully electric and plug-in hybrid cars, in the real world. The study was funded in part by the National Institutes of Health and just published in The Lancet Planetary Health. For the analysis, the researchers divided California into 1,692 neighborhoods, using a geographic unit similar to zip codes. They obtained publicly available data from the state’s Department of Motor Vehicles on the number of ZEVs registered in each neighborhood. ZEVs include full-battery electric cars, plug-in hybrids and fuel-cell cars, but not heavier duty vehicles like delivery trucks and semi-trucks. Next, the research team obtained data from the Tropospheric Monitoring Instrument (TROPOMI), a high-resolution satellite sensor that provides daily, global measurements of NO₂ and other pollutants. They used this data to calculate annual average NO₂ levels in each California neighborhood from 2019 to 2023. Over the study period, a typical neighborhood gained 272 ZEVs, with most neighborhoods adding between 18 and 839. For every 200 new ZEVs registered, NO₂ levels dropped 1.1%, a measurable improvement in air quality. To confirm that these results were reliable, the researchers conducted several additional analyses. They accounted for pandemic-related changes as a contributor to NO₂ decline, such as excluding the year 2020 and controlling for changing gas prices and work-from-home patterns. The researchers also confirmed that neighborhoods that added more gas-powered cars saw the expected rise in pollution. Finally, they replicated their results using updated data from ground-level monitors from 2012 to 2023.