Emissions of three powerful climate-warming greenhouse gases from China have surged over the past decade, according to the study.

When it comes to global warming, not all greenhouse gases are created equal: They vary widely in their Global Warming Potential (GWP), a measure of how much infrared heat radiation a gas absorbs in a given period of time after entering the atmosphere.

For example, when measured over a 100-year period, methane has a GWP greater than that of carbon dioxide (CO₂), and the greenhouse gases called perfluorocarbons (PFCs) have a GWP several thousand times that of CO.₂The atmospheric lifetime of greenhouse gases also varies greatly. Methane lasts in the atmosphere for about 10 years. CO₂ over 100 years, and up to tens of thousands of years for PFCs.

Given the high GWP and long lifetime of PFCs, their emissions could pose a major obstacle to achieving the goal of the Paris Agreement on climate change: limiting the increase in global average surface temperature to 1.5 degrees above pre-industrial levels.

Now, two new studies based on atmospheric observations and high-resolution atmospheric models across China have shown that emissions of three PFCs — tetrafluoromethane (PFC-14), hexafluoroethane (PFC-116) and perfluorocyclobutane (PFC-318) — have risen sharply in China over the past decade (2011 to 2020 or 2021).

Both studies found that Chinese emissions played a major role in the increase in global emissions of the three PFCs.

of Proceedings of the National Academy of SciencesThe study identified significant emission sources of PFC-14 and PFC-116 in China’s less populated western regions from 2011 to 2021, likely due to the concentration of aluminum industries in these regions.

The semiconductor industry also contributes some of the emissions found in the economically developed eastern region. These emissions come as a by-product of aluminum smelting or during the use of the two PFCs in the manufacture of semiconductors and flat panel displays. During the observation period, emissions of both gases in China increased by 78%, accounting for most of the increase in global emissions of these gases.

of Environmental Science and TechnologyThe study found that between 2011 and 2020, China’s PFC-318 emissions increased by 70% (accounting for more than half of the increase in global emissions of the gas), mostly in eastern China.

The regions with high PFC-318 emissions in China overlap with geographic areas with a high concentration of factories producing polytetrafluoroethylene (PTFE, commonly used in coatings for non-stick cookware), indicating that PTFE factories are the main source of PFC-318 emissions in China. These factories produce PFC-318 as a by-product.

“Using atmospheric observations from multiple monitoring sites, we not only determined the magnitude of PFC emissions, but also pinpointed their likely sources,” said Mingde An, a postdoctoral researcher in the MIT Center for Global Change Science (CGCS) and corresponding author of both studies.

“Identifying the actual source industries contributing to these PFC emissions and understanding why they are primarily emitted as by-products can provide guidance for developing region- and industry-specific mitigation strategies.”

“These three PFCs are primarily produced as unwanted byproducts during the manufacture of widely used industrial products,” said Ronald Prin, MIT professor of atmospheric sciences, director of the MIT Joint Program on Global Change Science and Policy and CGCS, and co-author of both studies. “Phasing out PFC emissions as quickly as possible would be highly beneficial to achieving global climate mitigation goals, and can likely be achieved through recycling programs and targeted technology improvements in these industries.”

The findings of both studies were derived in part from atmospheric observation data collected from nine stations in the Chinese network, including one station in the Advanced Global Atmospheric Gases Experiment (AGAGE) network. For comparison, total global emissions, as reported in the most recent United Nations Environment Programme/World Meteorological Organization Ozone Assessment Report, were measured from five relatively unpolluted “background” AGAGE stations distributed around the world.

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