Although the Marcone case is the largest smuggling prosecution anywhere so far, investigators believe that smuggled gas is used by other companies in the United States, and European customs officials have intercepted shipments of contraband gas arriving in Finland, Slovenia and Poland in the last two years, said Halvart Koeppen, a United Nations official who tracks illegal trade of the gas. This is “the tip of the iceberg,” he said.

Much of the global air-conditioning industry relies on the gas the way the auto industry does on gasoline. But while oil is getting harder to find and more expensive, HCFC-22 is becoming more abundant and remaining cheap on the global market.

“There is no question that this is inhibiting phaseout,” said Rajendra Shende, a former head of the United Nations Ozone Action Program who runs the Terre Policy Center, an environmental research institute in Pune, India.

In the meantime, the price of legitimately obtained gas has been rising in the United States and throughout Europe. That is because governments of industrialized nations, to comply with the ozone treaty known as the Montreal Protocol, restrict the use of the environmentally damaging gas in various ways. In the United States, the Environmental Protection Agency requires that companies obtain a license to make, sell or buy specific amounts of HCFC-22, with such “allowances” decreasing year by year.

The dwindling supply has led to pronounced spikes in price. What once cost retailers like Marcone $55 a canister was by 2009 going for $140 in the United States. By reducing the supply of the coolant and encouraging prices to rise, the United States government hoped to force manufacturers and consumers to scrap old machines and invest in more environmentally friendly, if more expensive, alternatives. But it has not worked out that way, especially in recessionary times when people hang on to old appliances and search for cheap shortcuts.

Many air-conditioning manufacturers have even figured out how to sidestep the 2010 ban on selling new machines containing HCFC-22, by offering unfilled air-conditioning compressors that service workers swap into existing units and then fill with the gas, creating refurbished machines that are as good as new.