A man from San Diego has pleaded guilty to a federal conspiracy charge in the first prosecution targeting the illegal importation of powerful greenhouse gases often used in cooling and refrigeration.

Federal authorities banned the import of these substances, known as hydrofluorocarbons, due to their significant role in climate change. According to the Climate and Clean Air Coalition, an initiative of the United Nations Environment Programme, their impact on global warming can be hundreds to thousands of times more potent than carbon dioxide per unit of mass.

Michael Hart, 58, was arrested in March for allegedly smuggling these illegal refrigerants across the border from Mexico multiple times without approval from the U.S. Environmental Protection Agency (EPA). This unprecedented case saw a grand jury indict Hart for allegedly violating the American Innovation and Manufacturing Act of 2020, known as the AIM Act, which forbids the import of such substances without EPA authorization.

Hart pleaded guilty on Tuesday to one count of conspiracy to violate the federal Clean Air Act and the AIM Act. In his plea agreement, he acknowledged purchasing hydrofluorocarbons—which can also be used in insulation, fire extinguishing systems, and aerosols—in Mexico and smuggling them into the U.S. for profit.

“Clean air is not for sale to the highest bidder,” stated U.S. Attorney Tara McGrath. “The Department of Justice will utilize all available tools to protect air quality and hold polluters accountable.” Assistant Attorney General Todd Kim emphasized that federal prosecutors are dedicated to enforcing the AIM Act and other laws aimed at preventing environmental damage.

“Congress has made it illegal to import certain refrigerants into the U.S. without allowances due to their significant contribution to climate change,” Kim noted. Hart’s court-appointed attorney did not respond to requests for comment.

According to his plea agreement, Hart promoted the illegal refrigerants on platforms like OfferUp and Facebook Marketplace, then ordered them from accomplices in Mexico. He would travel to Tijuana, pick up the refrigerants, and bring them across the border concealed under a tarp and tools.

The original indictment charged Hart with 13 counts, including conspiracy and unlawful importation, claiming he conspired with others to smuggle regulated refrigerant cylinders into the U.S. on at least five occasions—once in July 2022 and four times in October. It was alleged he sold the illegal refrigerants seven times in September and October of 2022.

As part of his plea deal for the conspiracy charge, prosecutors agreed to drop the other 12 counts. Hart will pay $1,500 in restitution for the disposal of the refrigerants. He faces a maximum sentence of five years in prison, although prosecutors have agreed to recommend a shorter term, along with a $250,000 fine.

Hart is set to be sentenced in December.