Source of large rise in emissions of unregulated ozone destroying substance identified

Smoke stack emissions

New research, involving an environmental scientist from Lancaster University, has discovered that emissions coming from China of the ozone-destroying chemical, dichloromethane, have more than doubled over the last decade.

The production of long-lived ozone-depleting gases, such as CFCs and HCFCs, is controlled by the United Nations Montreal Protocol – the international treaty designed to safeguard the ozone layer. Because of the Montreal Protocol controls, there has been a dramatic drop in emissions of the main substances that are responsible for depleting the stratospheric ozone layer, the part of the atmosphere that protects us from harmful solar radiation. As a result, the ozone layer is expected to recover back to 1980s levels in the mid to latter half of this century.

However, new research published in Nature Communications today shows that emissions of dichloromethane, an ozone-depleting chemical, from China have more than doubled in the last decade.

Dichloromethane is a so-called ‘Very Short-Lived Substance’, a class of chemical that are not controlled by the Montreal Protocol. Ongoing research at Lancaster led by Dr Ryan Hossaini of the Lancaster Environment Centre has previously shown that the atmospheric abundance of dichloromethane has increased rapidly with implications for a delayed recovery of the ozone layer.

The new study, led by the University of Bristol and Peking University, provides new evidence for the growth of dichloromethane emissions and highlights China as the major source region. The research combined atmospheric measurements of dichloromethane from nine locations in China, along with inverse modelling to derive the regional emission magnitude and distribution.

Minde An, a postgraduate student from Peking University, and visiting researcher at the University of Bristol, led the study. He said: “China is an important producer and user of compounds such as dichloromethane. Therefore, we wanted to examine measurements within the country to determine its contribution to global emissions.

“Our calculations revealed that China’s share of total global emissions grew from about one-third to two-thirds over the last decade. The global emissions increase since 2011 is the same size as the rise in emissions from China.

“We think that emissions of dichloromethane from China have increased because of its use as a solvent in various industrial applications and the expanding chloromethanes industry in China.”

The new analysis reveals:

· Emissions of dichloromethane from China grew from 231 (213–245) Gg/yr in 2011 to 628 (599–658) Gg/yr in 2019

· This regional increase in emissions is of the same magnitude as the inferred global emission rise of 354 (281−427) Gg/yr over the same period.

Lancaster Environment Centre’s Dr Ryan Hossaini, and his former PhD student Dr Tom Claxton, contributed to the analysis.

Dr Hossaini said: “If current levels of dichloromethane persist, we could expect to see a delay in ozone layer recovery of a few years. However, if they continue to grow at the rate we’ve seen over the last decade, it could lead to a delay of over a decade, though future emissions are highly uncertain.

“Of significance is the location of the emissions discovered in this study. Short-lived compounds like dichloromethane are partly destroyed in the lower atmosphere before they reach the ozone layer.

“However, in some parts of Asia, there are regions where the atmosphere can transport these substances to the stratosphere relatively quickly. This means emissions from these regions may pack a bigger punch than those released elsewhere.”

Professor Matt Rigby, from the University of Bristol’s School of Chemistry, said he was hopeful that these results can be repeated in the future to determine the impact of changes in regulation for dichloromethane and other compounds of interest to the Montreal Protocol.

He said: “One of the most important outcomes of this work is in showing what can be achieved through the close collaboration between scientists from around the world.

“These measurements from China are highly valuable for researchers and policymakers who are interested in the ozone layer and climate. We’re looking forward to continuing this work in future, to provide the parties to the Montreal Protocol with increasingly accurate information to help ensure that the recovery of the ozone layer stays on track.”

Paper title: ‘Rapid increase in dichloromethane emissions from China inferred through atmospheric observations’.

DOI: 10.1038/s41467-021-27592-y

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