Rapid reduction in CFC-11 emissions globally and from China

Our previous work showed how global emissions of CFC-11 rose, starting in 2013, and that a substantial fraction of these emissions originated from eastern China. In two new papers, we show, using atmospheric observations, that these signals have now reversed. Montzka et al. (2021) uses measurements in the background atmosphere to show a rapid reduction in global emissions in 2019, and Park et al. (2021) identifies a coincident decline from China.

Further details are available on the University of Bristol and NASA news pages, and elsewhere.

CFC-11 emissions from eastern China inferred from atmospheric observations. Image credit: NASA Earth Observatory

New CFC-11 emissions identified from China

In a new study in Nature, we show that emissions of the banned ozone depleting substance, CFC-11, have increased from eastern China since 2013. Our findings, based on analysis of data from the South Korean AGAGE station at Gosan and Japanese NIES station on Hateruma island, suggests that we have located a major fraction of the global emissions rise identified last year.

The implications of this finding are discussed in our article written for The Conversation, and a University of Bristol news item.

Simulated transport of CFC-11 to the Gosan (square) and Hateruma (circle) measurement stations for a day in December 2014. The coloured areas show regions where the measured concentrations would be strongly influenced by emissions sources. This information, from the Met Office NAME model, helped us identify new emissions coming from eastern China.

WMO Scientific Assessment of Ozone Depletion: 2018

The WMO Scientific Assessment of Ozone Depletion provides Parties to the Montreal Protocol with updates on scientific developments relating to ozone depleting substances and the recovery of the stratospheric ozone layer. Together with Andreas Engel and a fantastic team of co-authors, I wrote Chapter 1: Update on Ozone-Depleting Substances (ODSs) and Other Gases of Interest to the Montreal Protocol. Our chapter summarised some really interesting developments that have occurred over the last four years: an increase in global CFC-11 emissions, the identification of new sources of carbon tetrachloride (which helps to reduce the “gap” in our understanding of its global budget), a slow-down in the growth of HCFCs, and many other things. A huge thanks to all the authors whose work we relied on (> 200 papers, mostly from the last four years), and the monitoring networks that make it possible to keep track of changes the concentrations of these important gases.

WMO Scientific Assessment of Ozone Depletion: 2018. Image courtesy: NOAA ESRL.

An unexpected rise in global CFC-11 emissions

The Montreal Protocol has been extremely successful in limiting the emissions of ozone depleting substances such as CFCs. As we’ve shown in previous papers, emissions and atmospheric abundances of these compounds have declined in recent decades. Since 2010, the Protocol mandates that there should be essentially no new production of CFCs for emissive use anywhere in the world. Therefore, our finding, published in Nature, that the rate at which CFC-11 is declining in the atmosphere has slowed since 2013 was surprising. Using atmospheric observations from the National Oceanic and Atmospheric Administration, we show that about 10,000 tonnes of this compound are being emitted to the atmosphere each year. This result has since been supported by data from the Advanced Global Atmospheric Gases Experiment. There have been some good summaries of the work in the New York Times, Washington Post, Guardian, etc. Since the paper came out, work by the Environmental Investigation Agency has shown that CFC-11 may still be produced in China. The next step for us is to use atmospheric observations to try to narrow down the location

Indian methane emissions

Anita Ganesan’s paper on Indian methane emissions has been published in Nature Communications “Atmospheric observations show accurate reporting and little growth in India’s methane emissions“. As described in a University of Bristol news article, we used satellite data from GOSAT, combined with new measurements made in India, to show that India’s emissions hadn’t changed significantly in between 2010 and 2015. Furthermore, our estimates agree very well with India’s reports to the United Nations Framework Convention on Climate Change (UNFCCC).

GOSAT methane column measurements over India (Courtesy of Anita Ganesan)


Methane growth and global OH concentration

There have been several recent papers exploring the growth in methane that has been ongoing since 2007. In a new paper in PNAS, we explore whether changes in the global OH concentration could be playing a role. By looking at trends in methyl chloroform, we infer an intriguing rise and fall in OH over the last 20 years, which could explain some of the methane change. There are significant uncertainties remaining, and much more work is needed before we can determine with confidence the role of changes in both methane sources and sinks. This is the focus of the new UK-wide NERC-funded MOYA project which will be on-going for the next three years.

A MOZART simulation of OH concentrations (Courtesy: Angharad Stell)

There’s a University of Bristol news item, which provides more details on this story. The paper can be found here: Rigby et al., Role of atmospheric oxidation in recent methane growth, PNAS, doi:10.1073/pnas.1616426114, 2017


Examination of HFC emissions in the UK leads to Government rethink on how levels are recorded

Dan Say’s work on our re-evaluation of the UK’s HFC emissions featured on the University of Bristol News. Based on an analysis of atmospheric data, we found that the UK’s estimates of the emissions of HFC-134a, used in car air conditioning, were likely too high. Dan took a closer look at the UK inventory and found that estimates of the frequency at which car air conditioning units were refilled, and the number of cars with air conditioning units in them were likely over-estimated in the inventory.

The government is now re-evaluating the assumptions that go in to their HFC-134a calculations.


University of Bristol impact case study

Our work was featured as an impact case study in the 2013 Research Excellence Framework. A summary is on the University of Bristol website:

SF6 around the UK.
SF6 in the atmosphere around the UK.

“The amount of greenhouse gases that the UK produces is calculated annually by the Department for Energy and Climate Change (DECC). Researchers at the University of Bristol independently verify these estimates using atmospheric measurements, making the UK one of only three countries in the world that does so.

“Our work is used by the DECC for monitoring compliance with international and domestic legislation; identifying priorities for improving inventory accuracy; assessing the UK’s progress towards targets set in the Montreal and Kyoto Protocols; evaluating the impact of policy; and informing international negotiations.” – Professor Simon O’Doherty

The UK is signed up to the Montreal Protocol (which aims to reduce the amount of ozone depleting compounds emitted) and the Kyoto Protocol (which aims to reduce the amount of anthropogenic greenhouse gases in the atmosphere). These require the UK to report its emissions on a regular basis, but it’s not as straightforward as simply measuring the gases in the atmosphere.

Reporting the amount of man-made greenhouse gases that the UK produces annually is a challenging task. Like the other 191 countries that have signed up to the Kyoto protocol, the UK uses an inventory approach to estimate the emissions, as directly measuring anthropogenic greenhouse gases is too complicated. This involves estimating emissions from a variety of activities such as burning fossil fuels, agriculture and energy production. But the UK is one of only three countries that go one-step further, by using atmospheric measurements to validate these inventory calculations.

This independent verification is performed by researchers from the University of Bristol’s Atmospheric Chemistry Research Group which is part of the Cabot Institute and the School of Chemistry. Using a combination of physical measurement and sophisticated modelling techniques, Professor Simon O’Doherty and Dr Matt Rigby work in collaboration with Dr Alistair Manning from the UK Met Office to monitor the greenhouse gases in the atmosphere above the UK.

In order to do this, the researchers developed the UK DECC Network – a unique national greenhouse gas monitoring system comprising six stations making high-frequency measurements of key atmospheric trace gases. Analysis and interpretation of these observations using state-of-the-art modelling techniques enables the independent assessment of the UK’s adherence to the Montreal and Kyoto Protocols.

“Our work started more than 20 years ago when we provided data to the Government on the accumulation of ozone-depleting gases in the atmosphere resulting in the signing of the Montreal Protocol,” says O’Doherty. “We have been able to show how the use of chlorofluorocarbons (CFCs) has risen and fallen over the years and that direct measurement of atmospheric gases can be used to monitor the impact of legislation such as the Montreal Protocol.”

Back then O’Doherty only had one monitoring station at his disposal, but today he can use data from a network of stations across the country as well as aircraft, satellites and even ferries that measure climatically important gases such as carbon dioxide, methane and nitrous oxide. When combined with models of atmospheric gas transport, these observations provide an independent means of assessing natural and man-made emissions. As well as monitoring the UK’s compliance with international treaties, these data have been central to recent World Meteorological Office (WMO) Scientific Assessments of Ozone Depletion produced between 2007 and 2010 and to the Nobel Prize-winning Inter Governmental Panel on Climate Change (IPCC) Assessment of Climate Change published in 2007.

The data will also form the basis for negotiations of future targets for UK emissions.

“Future climate treaties will take recent emissions estimates as a baseline from which to plan emissions reductions. Therefore, it’s really important that we are able to get these estimates right, both in the UK and around the world, so that the burden for emissions reductions is shared in a fair way,” says Dr Rigby.

One of the biggest challenges for the future is distinguishing between natural and man-made greenhouse gases. O’Doherty and Rigby are now investigating new techniques that could measure different isotopic compounds and thus distinguish between anthropogenic and naturally emitted greenhouse gases.

Further information

Key facts:
• The underpinning research was funded by the Department for Energy and Climate Change, the Natural Environment Research Council and NASA.
• Man-made greenhouse gas emissions cannot currently be measured directly but instead are calculated by estimating emission from a number of activities such as the burning of fossil fuels.
• Bristol researchers independently verify these calculations by taking atmospheric measurements and using atmospheric models to calculate the source of the emissions.
• The UK now has a network of stations, managed by Professor Simon O’Doherty, that continuously monitor important atmospheric gases.
• The data from the monitoring stations is used to verify if the UK is adhering to the Montreal and Kyoto protocols, as well as to inform international policy on climate change.
• The UK is one of only three countries in the world that collects data and verifies emissions in this way.”