Every year, the U.S. government provides about $1 billion in tax credits to companies that produce what’s known as refined coal. It’s chemically treated coal that, when burned, supposedly emits less of the pollution that can harm human health.

But there’s a problem. Companies qualify for the tax credit using lab tests, “which could differ dramatically from what’s actually happening in the field at the power plants where the coal is burned,” says Brian Prest, a post-doctoral fellow at a research nonprofit called Resources for the Future.

He studied the actual air pollution emitted when companies burn refined coal.

“We look at actual field emissions, you know, what’s happening at the power plant,” he says. “We’re finding that the emission reductions fall far short of what the tax law says that they should be getting.”

What’s more, he says the tax credit can make it profitable for some older power plants to keep burning coal for longer. So it may actually increase carbon pollution and worsen global warming.

The tax credit is set to expire at the end of 2021.

“And it is an immediate policy question about whether we’re going to renew this or whether we should take the funds that would be used for this subsidy and perhaps use it for a better purpose,” he says.

Reporting credit: Sarah Kennedy/ChavoBart Digital Media.