Proposing a Co-Benefits Approach to Tackling Three Global Environmental Issues: Professor and Student Published in Top Science Journal

By John Butcher

Duke Kunshan professor Song Gao, co-leading an international team of science and policy scholars, is calling for limits on the use of certain chemical feedstocks* to help mitigate three urgent global environmental issues.

Their research, just published by Proceedings of the National Academy of Sciences of the United States of America (PNAS), a top-tier science journal, and reported on by the United Nations Environment Programme’s OzoNews, shows ozone-depleting substances (ODSs) and hydrofluorocarbons (HFCs) used as feedstocks have serious and growing environmental impacts in terms of plastic pollution, ozone depletion and climate change. They propose that existing international rules limiting their use be tightened.

“We are proposing a new, unified approach to tackling three environmental issues,” said Gao, professor of environmental science and chemistry, who is corresponding author of the paper. “Mounting environmental stresses related to them are closely interlinked, as shown in our paper, and must be addressed urgently, with science-based, policy-feasible strategies.”


Professor Song Gao, who is calling for limits on the use of certain chemical feedstocks

Gao co-led the research with collaboration from a team of scholars based in the U.S., Brazil, Costa Rica and Kenya, and Yiyao Wei, a senior studying environmental science/chemistry at DKU, who co-authored the PNAS paper. Upon examining academic papers, industrial patents and reference books dating back to the 1940s, they uncovered previously missing links between ODS and HFC feedstocks and products they are used to make. In particular, they illustrated a series of feedstock-derived reactions, including homogeneous and heterogeneous polymerization, that lead to the production of a range of plastics, rubbers, and other products resistant to environmental degradation that pose harm to human health and ecological balance.

The impact of using these raw manufacturing materials spans ozone damage and climate change, with the end products often leading to widespread plastic pollution in freshwater and marine environments. The paper proposes tackling these issues by further amending the Montreal Protocol on Substances that Deplete the Ozone Layer, an international agreement made in 1987, which restricts the production and use of ODSs and HFCs, the latter via the Kigali Amendment to the Montreal Protocol passed in 2016.

Over its 34 years of operation, the Montreal Protocol has been very successful, according to the paper’s comprehensive analysis, eliminating about 98 percent of ODSs and putting the stratospheric ozone layer on the path to recovery by the mid-21st century. Phasing out these substances has also avoided greenhouse gas emissions that otherwise could have equalled or exceeded the emissions of carbon dioxide, providing significant benefits for climate protection as well, he added.


Yiyao Wei, who co-authored the PNAS paper

“However, despite its success, the continuing production of feedstocks exempted from the Montreal Protocol is contributing to an unauthorized manufacture and market of chemicals,” said Gao, with recent measurements showing elevated emissions of several greenhouse gases with high global-warming potential, beyond levels explained by legal production and insignificant feedstock emissions.

“The outlook is alarming,” he added. “For example, continuing additions of CFC-11 (an ODS widely used as a refrigerant, foam blowing agent and solvent) beyond 2030 would impede successful healing of the ozone hole by a decade or more, according to latest model predictions.” To counter this, the paper proposes narrowing the exemptions for ODS and HFC feedstocks under the Montreal Protocol via further amendments and adjustments.

“Tightening protocol rules will make it easier to identify and prohibit feedstocks that otherwise could be diverted into unauthorized trade and emissions. Additionally, a newly identified co-benefit is that better controlling feedstocks at the upstream end would reduce plastics production, complement current downstream efforts to mitigate plastic pollution through recycling and clean-up programs, and provide a further economic incentive for innovation to find environmentally superior substitutes for existing plastics,” said Gao.

The research was a “fruitful collaboration” between experts in the physical sciences and social sciences via the lens of environmental mitigation, in particular integrating chemistry, atmospheric science and international law, said Gao.

“This academic paper provides a framework for policy makers, industries, and civil society to consider how stronger actions under the Montreal Protocol can complement other chemical and environmental treaties,” he added.

*feedstocks: raw materials used for producing certain products

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