Has the study made an effort to exclude any other factors? For example, a reduction in commute during the covid years?

> 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.

Seems pretty clear to me that that's controlled for.