The gases are hydrofluorocarbons (HFCs), a range of chemicals used in industry and retail primarily for cooling. These gases do not affect the ozone layer, unlike other banned refrigerants, but as greenhouse gases, they can be several thousand times more potent than carbon dioxide.

Despite commitments to reduce HFC usage, law enforcement agencies across the European Union struggle to track illicit shipments entering via Turkey, Russia or Ukraine, with smugglers resorting to increasingly sophisticated tactics to evade detection, the EIA stated following a two-year undercover investigation.

"It is still quite easy to find illegal HFCs on the European market", said Fin Walravens, a leading EIA activist. "There are signs that those trading them are adapting their methods, becoming more adept at trying to evade authorities", the activist warned. "If you manage to sneak in the most polluting and ugly gas undetected, you practically get the highest profit", he added.

Under the Kigali Amendment of 2016 to the Montreal Protocol, European countries and other industrialized nations committed to reducing HFC use by 85% between 2012 and 2036. To achieve this gradual reduction, authorized HFC producers and consumers are allocated quotas that are gradually reduced. However, given that demand remains strong, the gradual reduction has led to price increases, creating incentives for smugglers - many of whom are also authorized traders - to supply more goods, the report states.

"It's much easier if you have a license to simply exceed your quota: it's so hard to prove", Walravens explains. "Gradual reduction is intended to make HFCs more expensive and make people believe that alternatives are better and more profitable, but if illegal trade comes in and these sell at half the price, the whole system collapses", the activist warns.

An EIA investigation in 2021 suggested that illegally introduced HFCs into Europe could account for 20-30% of legally traded volumes, equivalent to up to 30 million tons of CO2. The new report did not provide a revised estimate, but Walravens stated that "very few things have changed".

China is the world's largest producer of HFCs, with 39 authorized manufacturers receiving production permits equivalent to 185 million tons of CO2 this year. In December, China issued new rules to penalize firms that exceed their quotas.

Even when alternative products are available, enforcing chemical phase-outs has been a major challenge, with some governments "unable or unwilling to take drastic action", said Ian Rae from the University of Melbourne, who served as a technical advisor to the Montreal Protocol. "There always seems to be demand from customers who were satisfied with the old product and are reluctant to switch to the new one, which may be more expensive", he explained.