High levels of a hazardous chemical polluted the air weeks after the Ohio train derailment, an analysis shows

Soon after the derailment of a Norfolk Southern train in East Palestine, Ohio, a team of researchers began roving the small town in a Nissan van.

It was February, less than three weeks after the disaster, and the van was outfitted with an instrument called a mass spectrometer, which can measure hundreds to thousands of compounds in the air every second.

The team was searching for harmful levels of air pollution. At the time, a primary concern was a flammable substance called vinyl chloride, because Norfolk Southern intentionally burned off the chemical...