After a coal-fired power plant in Pennsylvania closed, early-life health outcomes improved for babies across the border, in New Jersey.

The Portland Generating Station sits on the Delaware River, about two hours north of Philadelphia and right across the border from New Jersey. While in operation, it was one of the most prodigious emitters of sulfur dioxide in the nation, primarily affecting Jersey’s Warren, Sussex, Morris, and Hunterdon Counties. It stopped burning coal in 2014, after the Environmental Protection Agency demanded it reduce its pollution levels.

A new study shows that, after station’s closure, the likelihood of low birth weight went down 15 percent and the likelihood of pre-term birth decreased by nearly 30 percent.

Associate professor of economics at Lehigh University, Muzhe Yang, who led the study, says the improvements were primarily within 60 miles downwind of the plant, in New Jersey. His team focused on birth weight and pre-term births because previous findings have linked early-life health with outcomes in adulthood, such as education attainment and earnings.

The federal Clean Air Act, which is implemented at the state level, has a Good Neighbor provision. It requires states to prohibit emissions that would cause ambient air quality to exceed federal standards downwind. But Yang says the provision doesn’t always translate into action. “There’s no incentive, or incentive can be limited,” Yang said. “Upwind states might have different priorities: job creation, generating tax revenues, solving unemployment.”

In 2007, New Jersey filed a lawsuit, claiming the plant was responsible for fouling ambient air quality in the state. EPA agreed with New Jersey and imposed its own emissions rules on the plant; it was the first time a federal regulation overrode a state rule for a specific pollution source.

Yang says it’s a case that points to the importance of federal regulations over state rules.

“The wind can carry a lot of air pollutants. This is just a matter of fact. And the wind doesn’t recognize any borders,” Yang said.