Dr. Qing Liang, Research Physical Scientist, Atmospheric Chemistry and Dynamics Laboratory, NASA's Goddard Space Flight Center, Greenbelt, Maryland
Research Interests: Investigating the atmospheric budget and the transport of trace gases (e.g., human-made chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and the naturally emitted, short-lived halogen compounds) that impact stratospheric and tropospheric ozone and chemistry-climate interactions. Combining global two- and three-dimensional chemistry and climate models with NASA surface, airborne, and satellite data to improve understanding of atmospheric composition and the models used to represent it.
Research Highlights: Although it makes up just a tiny fraction of the atmosphere, ozone is crucial for life on Earth. Depending on where ozone resides in the atmosphere, it can protect or harm life. Most ozone is found in the stratosphere, the layer of the atmosphere 10 to 40 kilometers above the Earth’s surface, where it acts as a shield to protect humans and other life from the Sun’s harmful ultraviolet radiation. A weakening of this shield would make humans more susceptible to skin cancer, cataracts, and impaired immune systems. Closer to Earth, in the troposphere, the atmospheric layer from the surface up to about 10 kilometers, ozone is a harmful pollutant that can damage lung tissues when inhaled and the harm cell membranes of plants.
At any given time, ozone molecules are constantly formed and destroyed in the stratosphere. According to data records spanning several decades, the total amount of ozone in Earth’s atmosphere has remained relatively stable. Atmospheric ozone concentrations do vary in response to sunspots, seasons, latitude, and natural processes such as large volcanic eruptions, but these processes are well understood and predictable, and each natural reduction in in ozone levels has been followed by a recovery.
Beginning in the 1970s, however, scientific evidence began to show that the ozone shield was being depleted well beyond the scope of natural processes. The culprit was determined to be ozone-destroying substances (ODSs), such as CFCs, HCFCs, carbon tetrachloride (CCl4), methyl chloroform (C2H3Cl3), halons, and methyl bromide (CH3Br), that are emitted at the Earth’s surface and get swept up into the stratosphere. When exposed to intense UV light in this part of the atmosphere, ODSs release atoms of chlorine or bromine, each of which is capable of destroying thousands of ozone molecules before leaving the stratosphere.
Concerns about the effects of ODS on the stratospheric ozone layer, including awareness of the ozone “hole” (really a thinning of the atmosphere) that occurs over Antarctica each spring, prompted all countries worldwide to ban the use of CFCs. In 1987, an international agreement developed by the United Nations known as the Montreal Protocol led to the phase out of as many as 200 ODSs, including CFCs, HCFCs and other chemicals, known to be “long-lived” because they persist in the atmosphere for several years or longer.
Monitoring atmospheric concentrations of human-made ODSs and the chemistry-climate interactions that impact stratospheric and tropospheric ozone is the mission of the Atmospheric Chemistry and Dynamics Laboratory at NASA's Goddard Space Flight Center. Among the laboratory’s scientists working to meet this mission is Dr. Qing Liang, a research physical scientist and co-lead of the Goddard Earth Observing System (GEOS) Chemistry Climate Model (CCM) group.
NASA's GEOSCCM is a general circulation model with coupled chemistry used to simulate and study the dynamics, physics, chemistry, and biology of our planet. The scientists in the Atmospheric Chemistry and Dynamics Laboratory use it to study ozone and its influence on the state of the atmosphere and ocean.
In 2017, Liang published a commentary in Science (2017) in which she noted that, although the Earth’s ozone hole is showing signs of recovery decades after the Montreal Protocol banned many of the long-lived chemical compounds harmful to the ozone layer, delayed recovery of Earth’s stratospheric ozone remains a concern.
The Montreal Protocol does not prohibit the use of so-called very-short-lived substances (VSLSs), chemical compounds that remain in the atmosphere for periods of less than half a year, which may contribute to future stratospheric ozone depletion. In addition, the long-lived chemicals banned by the protocol still have a lingering impact on ozone, so any noncompliance with the protocol, including the continued emission of banned substances, is likely to have significant consequences for years to come. Finally, increasing emissions of naturally sourced ODSs, such as CH3Br and methyl chloride (CH3Cl), due to climate change may pose an even greater risk to ozone recovery.
To address these concerns, Liang’s Science commentary ends with a call for enhanced efforts to limit climate change, improved compliance with the Montreal Protocol, and continued monitoring for emissions of substances banned by the accord. Although the first and second of these three suggestions may be beyond the purview of Dr. Liang’s efforts, the third is well within the scope of her work in the Atmospheric Chemistry and Dynamics Laboratory and achievable through collaboration with scientists around the world.
A key component of Liang’s work is the use of global two- and three-dimensional chemistry models to simulate the atmospheric transport of the compounds known to affect tropospheric and stratospheric ozone. In the process, she uses a variety of NASA datasets from a variety of sources, including NASA’s Atmospheric Science Data Center (ASDC), as model inputs.
Among the ASDC datasets Liang uses in her modelling research are:
- The Intercontinental Chemical Transport Experiment (Phases A and B), an initiative to understand the transport and transformation of ozone and precursors, aerosols and precursors, and the long-lived greenhouse gases on transcontinental and intercontinental scales and assess their impact on air quality and climate.
- The Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission to investigate the impact of human pollutions, biomass burning, and stratospheric air on ozone abundance in the lower atmosphere.
- Measurements of Pollution in the Troposphere (MOPITT), a dataset from the MOPITT instrument aboard NASA’a Terra satellite used to measure tropospheric carbon monoxide on a global scale.
- Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS), an effort combining observations from satellites, aircraft, balloons, and the surface sensors to assess concentrations of pollution and natural emissions in the atmosphere primarily over the southern United States.
Located in the Science Directorate at NASA'S Langley Research Center in Hampton, Virginia, ASDC collaborates with the directorate's Climate Science, Atmospheric Composition, and Chemistry and Dynamics Branches to study changes in the Earth and its atmosphere. ASDC archives, documents, and distributes more than 1,000 archived data sets from several sources (e.g., aircraft, ground stations, satellites, and so on) and modeled data products to support more than 50 research projects pertaining to the Earth’s atmosphere.
For example, Liang was part of a team that published a study in Geophysical Research Letters (2018) detailing their use of atmospheric measurements of CCl4 from the NASA-funded Advanced Global Atmospheric Gases Experiment (AGAGE) — a network of monitoring stations led by the Center for Global Change Science at the Massachusetts Institute of Technology, the Scripps Institute of Oceanography, and NOAA's Global Monitoring Division — in East Asia and the NASA KORUS-AQ (Korea-United States Air Quality) mission to identify the magnitude and location of emissions from this region between 2009 and 2016.
Although the production and consumption of CCl4 for dispersive applications has been banned under the Montreal Protocol since 2010, it continues to be produced for certain permitted exemptions and for nondispersive feedstock applications. These feedstock uses are unregulated, since it is assumed that nearly all CCl4 produced is subsequently used, recycled, or destroyed. However, the researchers found that there were significant, ongoing emissions from eastern China and that these unauthorized releases explained a large part of the unaccounted-for emissions. By documenting the continued emission sources of this important ODS, Liang and her colleagues showed that more could be done to speed up the recovery of the ozone layer.
This work added to the findings of a previous study from 2014 in which Liang and her colleagues used source and sink data from the AGAGE network in the NASA 3-D GEOS Chemistry Climate Model to determine that CCl4 was making its way into the atmosphere. The United Nations Environmental Program has stated there were zero emissions of this ozone-destroying gas during the years of 2007 to 2012. Yet, based on their model simulations, Liang and her fellow researchers reported that, from 2000 to 2012, approximately 39,000 gigagrams CCl4 were released into the atmosphere each year.
“Carbon tetrachloride accounts for about 11 percent of the total chlorine that destroys stratospheric ozone, so it’s a pretty major compound,” Liang said in a NASA-produced video about the findings.
In addition to these unauthorized releases, Liang and her team also discovered that, based on the slow decline of observed levels of CCl4 in the atmosphere, the chemical lifetime (i.e., the time it takes the gas to breakdown) of CCl4 is longer than previously thought. The current lifetime expectancy is 25 years. However, according to the findings of Liang and her team, 35 years is a more accurate estimate.
Liang has also produced global simulations used in three recent and related research papers that document the detection and subsequent decline of Trichlorofluoromethane (CFC‐11, CFCl3), a major anthropogenic ozone‐depleting substance and greenhouse gas, from eastern China beginning in 2013.
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.
Representative data products used or created:
Available through ASDC:
- Intercontinental Chemical Transport Experiment-Phase A doi:10.5067/aircraft/INTEXA/aerosol-tracegas
- Intercontinental Chemical Transport Experiment-Phase B doi:10.5067/Aircraft/INTEXB/Aerosol-TraceGas
- Measurements of Pollution in the Troposphere (MOPITT) doi:10.5067/TERRA/MOPITT/MOP03J_L3.108
- Stratospheric Aerosol and Gas Experiment (SAGE) doi:10.5067/ERBS/SAGEII/SOLAR_BINARY_L2-V7.0
- Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEA4CRS) via NASA's Langley Resource Center Airborne Science Data for Atmospheric Composition website.
Other data products used:
- Advanced Global Atmospheric Gases Experiment (U.S. Department of Energy, Oak Ridge National Laboratory)
- Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS, Goddard Earth Sciences Data and Information Services Center), Phases A and B doi:10.5067/SQSWDF366LDY
- Atmospheric Tomography mission (Oak Ridge National Laboratory Distributed Active Archive Center) doi:10.3334/ORNLDAAC/1597
- Global Ozone Chemistry And Related trace gas Data records (GOZCARDS) Merged Data for Nitrous Oxide doi:10.5067/MEASURES/GOZCARDS/DATA3013
- Korea-United States Air Quality (KORUS-AQ) doi:10.5067/Suborbital/KORUSAQ/DATA01
- Ozone Monitoring Instrument/Aura Formaldehyde (HCHO) (Goddard Earth Sciences Data and Information Services Center) doi:10.5067/Aura/OMI/DATA2016
- Temperature (TB) dataset (Global Hydrometeorology Resource Center Distributed Active Archive Center) doi:10.5067/TC4/AMPR/DATA101
- Western, L., & Rigby, M. (2021, January 27). Data and code for emissions of CFC-11 and related substances from eastern China, doi:10.17605/OSF.IO/QP2BE
Read About the Research:
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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