For many years there was no question that the air in Eliot was polluted by coal-burning Schiller Station, just across the Piscataqua River in New Hampshire. You could see tiny black particles that were carried in the air and that would collect on walls, windows, cars and the surface of puddles. The same particles were drawn deep into Eliot residents’ lungs. Many in town associate the plant with a wide range of respiratory ailments, from asthma and bronchitis to lung cancer.

The ash particles are gone, but Eliot residents question whether pollution that can’t be seen is still wafting over the river and making people sick. Armed with a computer modeling study conducted by the Sierra Club, locals have petitioned the federal Environmental Protection Agency to study whether sulfur dioxide from the plant is making the air unhealthy in Eliot.

The request is more than reasonable. People who have lived downwind of the plant have been breathing its fumes and have a right to know if their health has been jeopardized.

Regulators allowed Schiller Station to operate for decades with few controls, and the people of Eliot should not have to trust them or the plant’s owners, both of whom have always said there is nothing to worry about.

Built in the 1950s, Schiller once burned coal around the clock. But as regulations have grown more strict, it is used only when demand for power peaks. One of its three boilers has been converted from coal to biomass, which has also reduced its emissions. Air testing in New Hampshire has not indicated any violations of clean air standards.

But the monitoring was not done in Eliot, and the Sierra Club’s computer modeling indicates that it’s the Maine town that would have received the brunt of the pollution.

That was certainly the case when the plant was emitting particulate matter that was visible to the naked eye, so thick, in fact, the plant’s owners offered to power-wash houses in Eliot for no charge. It stands to reason that an invisible gas would follow the same track.

And the testing that has been done is out of date. Under old rules, air quality had to be bad for 24 hours to result in a violation.

Environmental regulators in New Hampshire don’t have the jurisdiction or incentive to monitor the air after it leaves the state. This is really a job for federal authorities.

Maine’s congressional delegation should put pressure on the EPA to conduct this research. The people of Eliot have been on the wrong end of these smokestacks for too long. It’s time they’ve got some answers about what’s in their air.