A San Diego man has pleaded guilty to a federal conspiracy charge in the first ever prosecution targeting the illegal importation of potent greenhouse gases typically used for cooling and refrigeration. Federal lawmakers outlawed the importation of the substances, known as hydrofluorocarbons, because of their harmful contribution to climate change. “Their impact on global warming can be hundreds to thousands of times greater than that of carbon dioxide per unit of mass,” according to the Climate and Clean Air Coalition, an initiative of the United Nations Environment Programme. Michael Hart, 58, was arrested in March for allegedly smuggling the illegal refrigerants across the border from Mexico on multiple occasions without approval from the U.S. Environmental Protection Agency. In a first-of-its-kind prosecution, a grand jury indicted Hart for allegedly violating the American Innovation and Manufacturing Act of 2020, known as the AIM Act, which prohibits the importation of such substances without EPA approval. Hart pleaded guilty Tuesday to a single count of conspiracy to violate the federal Clean Air Act and the AIM Act. He admitted in a plea agreement that he bought hydrofluorocarbons — which in addition to refrigeration and air conditioning can also be used in building insulation, fire extinguishing systems and aerosols — in Mexico and then smuggled them across the border to sell for a profit in the U.S. “Clean air is not for sale to the highest bidder,” U.S. Attorney Tara McGrath said in a statement. “The Department of Justice will use every tool at our disposal to protect air quality and hold criminal polluters accountable.” Assistant Attorney General Todd Kim from the Department of Justice’s Environment and Natural Resources Division said federal prosecutors were committed to enforcing the AIM Act and other laws seeking to prevent environmental harm. “Congress made it illegal to import certain refrigerants into the United States without allowances because of their documented and significantly greater contribution to climate change,” Kim said in a statement. Hart’s court-appointed attorney did not respond to a request for comment Wednesday. According to his plea agreement, Hart advertised the illegal refrigerants on OfferUp, Facebook Marketplace and other internet sites, then placed orders for the substances with co-conspirators in Mexico. Hart then drove to Tijuana, picked up the refrigerants and brought them across the border concealed under a tarp and tools. The original indictment charged Hart with 13 counts of conspiracy, importation contrary to law and sale of merchandise imported contrary to law, alleging that Hart conspired with others to smuggle cylinders of the regulated refrigerants into the U.S. on at least five occasions — once in July 2022 and four times in October of that year. The indictment alleged that he made sales of the illegal refrigerants on seven occasions in September and October of 2022. As part of his plea deal on the conspiracy charge, prosecutors agreed to dismiss the other 12 counts. Hart agreed to pay $1,500 in restitution for the cost of disposing of the refrigerants. He faces a maximum of five years in prison, though prosecutors agreed to recommend a lesser term, and a fine of $250,000. Hart is scheduled to be sentenced in December.