It's the biggest environmental whodunit of the year, and after following a trail of clues, The New York Times may have cracked the case on why ozone-destroying chemicals are once again polluting our atmosphere.
The unexpected and mysterious surge in illegal chemicals called chlorofluorocarbons (CFCs) appears to be coming from Xingfu, a rural industrial town in China's Shandong province.
Last month, scientists at the US National Oceanic and Atmospheric Administration (NOAA) noticed a surprising increase in atmospheric CFC-11. It was surprising because under the 1987 Montreal Protocol, the world agreed to stop producing this ozone-thinning chemical altogether by 2010.
In 2013, the protocol was declared a huge success, slowly shrinking the giant hole in the ozone layer that forms over Antarctica each September. Today, from their peak in 1993, CFC-11 concentrations have declined by 15 percent.
Now, however, it appears that some factories in China have been producing CFC-11 in spite of the ban, violating the agreement and jeopardising the future of Earth's ozone layer.
After tracking down documents and doing a series of interviews, journalists at The NYT and independent investigators have found that factories in China have been using CFC-11 as a cheap way to produce foam insulation for refrigerators and buildings.
Meanwhile, government enforcement in the region has been poor, with reports of illegal CFC production going back several years. While government oversight is clearly in need of improvement, some of these factories are so small that they can slip through the cracks of regulation without detection.
"Illegal production and use is highly concealed, evidence is hard to obtain, and it's quite difficult to crack cases," wrote Changying Shao, an environment official in Shandong, in a report published last year.
"Among the cases of lawbreaking in recent years, only a small number of the suspects have received the punishment they deserve."
The use of CFC-11 in Xingfu is nothing new, and as a result, some experts have voiced scepticism that the surge in CFCs can be attributed to Xingfu's factories alone.
Today, CFC-11 emissions are about the same as they were nearly 20 years ago, which suggests that there are a whole bunch of other factories that are ignoring the international ban as well.
The head of the United Nations Environment Program, Erik Solheim, who oversees the Montreal Protocol told The NYT that while China's actions are "nothing short of an environment crime which demands decisive action," we still need to dig deeper.
"Based on the scale of detected emissions there is good reason to believe the problem extends beyond these uncovered cases," he said.
You can read the full report at The New York Times.