It didn’t matter that the mothers there had advantages that low-income mothers don’t: money and access to private health care. Their babies still appeared to suffer from the effects of air pollution, specifically wind-borne sulfur emissions. The study authors say stronger federal regulation of emissions from coal-fired plants is needed to safeguard human health.

Plenty of research has looked at the negative effects of air pollution made worse by smoke drifting from coal-burning power plants. But this study by scientists at the University of Pennsylvania and Lehigh University is the first to assess cross-state sulfur dioxide pollution from a specific plant, the Portland Generating Station in Northampton County, Pa., and to use atmospheric dispersal modeling to link it to downwind areas — in this case, Warren, Morris, Hunterdon and Sussex counties in New Jersey.

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“We have this very unique situation where the source is uniquely identified,” said lead author Muzhe Yang, an associate professor in the Lehigh economics department. “Most studies focus on low-wage areas, and we looked at a wealthy region. We are filling a very important gap. This is just the beginning step, an impact on early life through birth outcomes.”

The study, published in the Journal of Policy Analysis and Management, and co-authored by Rhea Bhatta, a digital analyst at the University of Pennsylvania, lays out its rationale in its introduction: to “provide causal estimates of the impact of prenatal exposure to power plant emissions on birth weight … for a wealthy region of the United States.”

Yang said the study’s conclusions suggest that the Environmental Protection Agency should be more involved in settling interstate disputes because of health concerns. The Supreme Court ruled in 2015 that the Clean Air Act gave the EPA the authority to limit downwind pollution that crosses state borders.

“The problem is, who should have the authority to solve cross-border pollution problems?” Yang said. “We are not providing any solutions, but we want to raise this question that deserves more attention.”

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At the same time, even while fighting pollution sources beyond their borders, downwind states also must work to improve their own air quality to mitigate the harm to residents, he noted.

Finding the source of the Mid-Atlantic region’s sulfur dioxide pollution wasn’t hard. New Jersey has been at war with the power plant on its border with Pennsylvania for years. In 2010, New Jersey’s Department of Environmental Protection filed a petition with the EPA after studies showed the Portland Generating Station had emitted more than 30,000 tons of sulfur dioxide during the previous year — double the sulfur emissions from all electricity-generating plants in New Jersey.

A trajectory analysis using atmospheric dispersal modeling showed that the wind transported the sulfur emissions to Warren County. A month later, New Jersey filed a second petition with evidence that pollution from the facility also reached three other counties, including the borough of Chester in Morris County, 21 miles southeast. The EPA ruled against the plant, which eventually stopped burning coal in 2014.

“It’s possible that other air pollutants emitted from PGS, such as nitrogen dioxide and carbon monoxide, are also able to reach New Jersey through prevailing wind in this region,” the study says, without offering any proof.

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To examine the potential impact on pregnant women, the authors concentrated on a treasure trove of information from those New Jersey petitions. They also relied on weather-monitoring sources that calculated daily and monthly average wind directions and the state’s atmospheric dispersal modeling. Finally, they used New Jersey’s state inpatient database for a look at all live births starting in 1990, five years before sulfur dioxide emissions from the Pennsylvania plant were first recorded. Multiple births were excluded.

By combining wind analyses with birth information obtained from the database, which includes Zip codes, the study determined that from 1990 to 2006, the likelihood of a woman delivering a low- or very low-birthweight baby was significantly higher in the four counties studied than in areas of comparable affluence.

Regardless, the rates were still much lower than the national average for areas in similar proximity downwind of a coal-fired power plant.

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The state database provided “demographic variables on the sex and race of an infant and the health insurance status of the mother” though not the mother’s age or educational attainment, according to the study. But it contained the women’s Zip codes, so researchers zeroed in on that.

In the four counties, the infants were more likely to be white and their mothers “slightly more likely to have private health insurance and slightly less likely to have to self-pay for the childbirth” — a finding that aligned with census data. The counties had annual household incomes higher than the state’s $71,600 average and much higher than the national average of $53,000, placing them in a wealthy category that Yang said meant the women likely had better health care options. It probably also indicated they had more access to technology that could mitigate pollution than low-income residents studied in previous research.

As for the Portland Generating Station, it found a new way to generate electricity. It switched from dirty coal to dirty diesel in 2014, and a new fight over pollution started.

Correction: A previous version of this story gave the incorrect location of the Portland Generating Station.