In March, the Trump administration created a novel way for companies to potentially avoid complying with environmental rules: Simply send an email to the Environmental Protection Agency and request an exemption.

In response, representatives of at least 15 coal-burning power plants, four steel mills, four chemical facilities and two mines wrote emails to the E.P.A. this spring, according to documents reviewed by The New York Times.

All 15 coal plants were ultimately exempted from requirements to curb several hazardous air pollutants, including mercury, a neurotoxin that can cause developmental problems in infants and children. All four chemical facilities were exempted from restrictions on other harmful air pollutants, including ethylene oxide, a gas linked to several types of cancer.

Those email exemptions were part of a broader wave of more than 100 granted so far by the Trump administration to facilities across the country, including oil refineries and sites that process a type of iron ore. The exemptions apply to rules that were set to take effect in the coming years.

The Sierra Club, an environmental group, obtained the E.P.A. documents by filing a Freedom of Information Act request. Patrick Drupp, the group’s director of climate policy, said in an interview that “communities have a right to know if coal plants, chemical plants or steel plants are actively trying to get around regulations that are designed to protect those communities.”