The first of these papers, published in Nature (2019), discussed how members of the atmospheric science community expected emissions of CFC-11, which is controlled under the Montreal Protocol, to continue declining, despite continued, small emissions of CFC-11 from aging air conditioning and refrigeration systems and other industrial activities. However, based on AGAGE monitoring station data and outputs from NASA’s atmospheric and climate models, NOAA issued a report in 2018 indicating that the decrease in levels of atmospheric CFC-11 were smaller-than-expected, meaning that, somewhere, CFC-11 was being emitted in larger quantities than anticipated.
Given the widespread geographic distribution of the stations within the AGAGE network, two stations — the South Korean Gosan AGAGE station, run by Kyungpook National University in South Korea, and the AGAGE station on Hateruma Island in Japan, run by Japan's National Institute of Environmental Studies — were able to identify eastern China as a significant source of some, although not all, of the increased CFC-11 emissions.
In the second of these studies, published in the Journal of Geophysical Research: Atmospheres (2020), Liang and her colleagues used a Goddard two‐dimensional model, which has been used to conduct World Meteorological Organization ozone assessments, to demonstrate how potential future emissions of CFC-11 might impact stratospheric ozone, which protects the Earth's biosphere from harmful ultraviolet radiation and is key in determining the atmosphere’s radiative balance. Through their work, which incorporated Ground based total column ozone measurement data and Global Ozone Chemistry And Related trace gas Data records (GOZCARDS), Liang and her colleagues showed that, should the increased emissions observed during 2013–2016 continue to 2100, ozone depletion would be substantial. Under this scenario, the restoration of global ozone to 1980 levels would be postponed from mid‐2052 to 2060 and result in an additional 1 percent of global ozone depletion by 2100. Although there is uncertainty in projecting future emissions, Liang and her colleagues noted that the forecast ozone response is strongly dependent on the total CFC‐11 emissions over time, allowing for a simple measurement of ozone depletion based on the cumulative amount of emissions.
Since the problem was detected, and after publication of NOAA’s 2018 report on the emissions, the Chinese government and industry officials have taken effective measures to stop the illegal production and use of CFC-11. The return of CFC-11 emissions to pre-2013 levels in eastern China was documented in the third of these studies, published in Nature (2021). Yet, despite this success story, continued monitoring for elevated emissions of CFC-11 is necessary, both to ensure compliance with the Montreal Protocol and the continued recovery of the ozone layer.
“Although we’re very happy with the progress of the Montreal Protocol, it is of critical importance for NASA, NOAA, and other international agencies to continue atmospheric observations of these gases,” said Liang in a NASA video about the findings of the paper published in Nature. “Without these measurements, it is not possible for us to detect problems and take action to solve them.”
Fortunately, given that it’s the Atmospheric Chemistry and Dynamics Laboratory’s mission to monitor atmospheric concentrations of human-made ODSs and the chemistry-climate interactions that impact stratospheric and tropospheric ozone, these observations and measurements won’t end anytime soon. The laboratory’s Ozone Hole Watch website offers the latest information on the status of the ozone layer over Antarctica and its Ozone and Air Quality website offers data from NASA’s fleet of Earth-observing satellites whose instruments observe air pollution from around the world.
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Park, S., Western, L., Saito, T., Redington, A., Henne, S., Fang, X., Prinn, R., Manning, A., Montzka, S., Fraser, P., Ganesan, A., Harth, C., Kim, K., Krummel, P., Liang, Q. Mühle, J., O’Doherty, S., Park, H., Park, M., Reimann, S., Salameh, P., Weiss, R., & Rigby, M. (2021). A decline in emissions of CFC-11 and related chemicals from eastern China. Nature, 590(7846): 433-437. doi:10.1038/s41586-021-03277-w
Fleming, E.L., Newman, P.A., Liang, Q., & Daniel, J.S. (2020). The Impact of Continuing CFC‐11 Emissions on Stratospheric Ozone. Journal of Geophysical Research: Atmospheres, 125(3). doi:10.1029/2019jd031849
Rigby, M., Park, S., Saito, T., Western, L.M., Redington, A.L., Fang, X., Henne, S., Manning, A.J., Prinn, R.G., Dutton, G.S., Fraser, P.J., Ganesan, A.L., Hall, B.D., Harth, C.M., Kim, J., Kim, K.-R., Krummel, P.B., Lee, T., Li, S., Liang, Q., Lunt, M.F., Montzka, S.A., Mühle, J., O’Doherty, S., Park, M.-K., Reimann, S., Salameh, P.K., Simmonds, P., Tunnicliffe, R.L., Weiss, R.F., Yokouchi, Y., & Young, D. (2019). Increase in CFC-11 emissions from eastern China based on atmospheric observations. Nature, 569 (7757): 546-550. doi:10.1038/s41586-019-1193-4
Lunt, M.F., Park, S., Li, S., Henne, S., Manning, A.J., Ganesan, A.L., Simpson, I.J., Blake, D.R., Liang, Q., O'Doherty, S., Harth, C.M., J. Mühle, J., Salameh, P.K., Weiss, R.F., Krummel, P.B., Fraser, P.J., Prinn, R.G., Reimann, S., & Rigby, M. (2018). Continued Emissions of the Ozone-Depleting Substance Carbon Tetrachloride From Eastern Asia. Geophysical Research Letters, 45 (20): 11423-11430. doi:10.1029/2018gl079500
Liang, Q., Strahan, S.E., & Fleming, E.L. (2017). Concerns for ozone recovery. Science, 358 (6368): 1257-1258. doi:10.1126/science.aaq0145
Liang, Q., Newman, P., Daniel, J.S., et al. (2014). Constraining the carbon tetrachloride (CCl4) budget using its global trend and inter-hemispheric gradient. Geophysical Research Letters, 41 (14): 5307-5315. doi:10.1002/2014GL060754
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