A follow-up investigation by NOAA scientists into the sudden increase in emissions of an ozone-destroying chemical between 2010 and 2018 has determined that three regions of Asia – not just one – were responsible for rising emissions of the banned chemical.
In a paper published in the journal Atmospheric Chemistry and Physics, analysis of air samples, including those taken during two major airborne research campaigns, confirmed increased emissions of CFC-11 from eastern China, but also found significant increasing emissions from temperate western Asia and tropical Asia.
Lead author Lei Hu, a CIRES scientist who studies CFCs and other ozone-depleting trace gases working at NOAA’s Global Monitoring Laboratory, said her team analyzed a large set of high-quality, well-distributed air samples collected by the scientific community during that time period.
“Once we analyzed NOAA measurement data from samples collected all around the world and at different elevations in the atmosphere, we were able to account for most of the observed increase in emissions,” Hu said.
Engineering triumph turned planetary scourge
Chlorofluorocarbons, or CFCs, were once considered a triumph of modern chemistry. Stable and versatile, these chemicals were used in hundreds of products, from military systems to the ubiquitous can of hairspray.
In 1987, NOAA scientists were part of an international team that proved this family of wonder chemicals was damaging Earth’s protective ozone layer and creating the giant hole in the ozone layer that has formed over Antarctica every year. The Montreal Protocol, signed later that year, committed the global community to phasing out their production. Production of the second-most abundant CFC, CFC-11, would end completely by 2010. Except that it didn’t.
Years of vigililance yielded unwelcome discovery
In 2018, Hu’s colleague Stephen Montzka, published a paper in the journal Nature that rocked the scientific world by describing what turned out to be the first known violation of the Montreal Protocol’s ban on the production and use of CFC-11. Based on analysis of data collected at the Global Monitoring Laboratory worldwide network of sampling sites, scientists were able to demonstrate that emissions of CFC-11 had mysteriously increased by 25%, suggesting the presence of new production in violation of the protocol.
Montzka and NOAA colleagues contributed to a companion study led by scientists with the Advanced Global Atmospheric Gases Experiment (AGAGE) and published in 2019, which determined that at least 40 to 60 percent of the CFC-11 global emissions increase came from eastern mainland China. However, it remained unclear where the rest of the emission increase came from.
Airborne sampling campaigns were key to new findings
In this new work, by augmenting NOAA’s ongoing sampling network at Earth’s surface with measurements from the two short-term airborne campaigns, ATom and HIPPO, NOAA’s continuous in-situ air measurements and regular aircraft profiling, the researchers were able to enhance their ability to quantify emissions on regional to continental scales, particularly from Asia.
With the additional data, time, and the help of NOAA’s HYSPLIT atmospheric transport model, which allowed scientists to track air motions back in time and identify upwind source regions, Hu’s research team from the Global Monitoring and Chemical Sciences labs were able to attribute nearly all of the 2012-2017 emission rise to the three regions in Asia.
Sampling network boost would improve precision of source identification
Despite the success in detecting the rising CFC emissions, there are still substantial uncertainties in the estimates of regional and continental emissions derived by the researchers, as significant gaps remain in global sampling networks, Hu said.
These sampling gaps mean that scientists could have difficulty identifying the sources of any future unexpected increases in global CFC-emissions, changes could go unattributed, making in-time recovery of the ozone layer more difficult.
Additional sampling locations and frequency, particularly downwind of undersampled regions such as Asia, Africa, and South America, would improve scientists’ understanding of global atmospheric composition changes, and make mitigation of associated ozone layer and climate impacts more timely, efficient, and effective.
On the other hand, failure to address the substantial sampling gaps mean that unexpected future global changes could go unattributed, making in-time recovery of the ozone layer more difficult.]
This research was funded by NOAA, NASA, and the National Science Foundation, with support from CIRES.