The recovery of the stratospheric ozone layer relies on the continued decline in the atmospheric concentrations of ozone-depleting gases such as the chlorofluorocarbons 1. The atmospheric concentration of trichlorofluoromethane (CFC-11), the second most abundant chlorofluorocarbon, has declined substantially since the mid-1990s 2. A recently reported slowdown in the decline of the atmospheric concentration of CFC-11 after 2012, however, implies that global emissions have increased 3,4. A concurrent increase in CFC-11 emissions from eastern Asia contributes to the global emission increase, but the location and magnitude of this regional source remain uncertain 3. Here we use high-frequency atmospheric observations from Gosan, Republic of Korea and Hateruma, Japan, together with global monitoring data and atmospheric chemical transport model simulations to investigate regional CFC-11 emissions from eastern Asia. We find that emissions from eastern mainland China are 7.0 ± 3.0 Gg yr-1 higher in 2014-2017 compared to 2008-2012, and the emissions increase arises primarily around the northeastern provinces of Shandong and Hebei. This increase accounts for a substantial fraction (about 40-60%, or more) of the global CFC-11 emission rise. We find no evidence for a significant increase in emissions from any other eastern Asian countries or other regions of the world where available data allow for the detection of regional emissions. Attribution of any remaining fraction of the global CFC-11 emission rise to other regions is limited by the sparsity of long-term measurements of sufficient frequency near potentially emissive regions. Multiple considerations suggest that the increase in CFC-11 emissions from eastern mainland China is likely the result of new Energy & Industrial Strategy (BEIS, UK, formerly the Department of Energy and Climate Change (DECC)) contract 1028/06/2015 to the University of Bristol and the UK Meteorological Office. Ragged Point, Barbados is supported by the National Oceanic and Atmospheric Administration (NOAA, USA), contract RA-133-R15-CN-0008 to the University of Bristol. L.W., M.L.

Abstract. We present a hierarchical Bayesian method for atmospheric trace gas inversions. This method is used to estimate emissions of trace gases as well as "hyper-parameters" that characterize the probability density functions (PDFs) of the a priori emissions and model-measurement covariances. By exploring the space of "uncertainties in uncertainties", we show that the hierarchical method results in a more complete estimation of emissions and their uncertainties than traditional Bayesian inversions, which rely heavily on expert judgment. We present an analysis that shows the effect of including hyper-parameters, which are themselves informed by the data, and show that this method can serve to reduce the effect of errors in assumptions made about the a priori emissions and model-measurement uncertainties. We then apply this method to the estimation of sulfur hexafluoride (SF 6 ) emissions over 2012 for the regions surrounding four Advanced Global Atmospheric Gases Experiment (AGAGE) stations. We find that improper accounting of model representation uncertainties, in particular, can lead to the derivation of emissions and associated uncertainties that are unrealistic and show that those derived using the hierarchical method are likely to be more representative of the true uncertainties in the system. We demonstrate through this SF 6 case study that this method is less sensitive to outliers in the data and to subjective assumptions about a priori emissions and model-measurement uncertainties than traditional methods.

Abstract. Sulfur hexafluoride (SF6) has a global warming potential of around 22 800 over a 100-year time horizon and is one of the greenhouse gases regulated under the Kyoto Protocol. Around the year 2000 there was a reversal in the global SF6 emission trend, from a decreasing to an increasing trend, which was likely caused by increasing emissions in countries that are not obligated to report their annual emissions to the United Nations Framework Convention on Climate Change. In this study, SF6 emissions during the period 2006–2012 for all East Asian countries – including Mongolia, China, Taiwan, North Korea, South Korea and Japan – were determined by using inverse modeling and in situ atmospheric measurements. We found that the most important sources of uncertainty associated with these inversions are related to the choice of a priori emissions and their assumed uncertainty, the station network as well as the meteorological input data. Much lower uncertainties are due to seasonal variability in the emissions, inversion geometry and resolution, and the measurement calibration scale. Based on the results of these sensitivity tests, we estimate that the total SF6 emission in East Asia increased rapidly from 2404 ± 325 Mg yr−1 in 2006 to 3787 ± 512 Mg yr−1 in 2009 and stabilized thereafter. China contributed 60–72% to the total East Asian emission for the different years, followed by South Korea (8–16%), Japan (5–16%) and Taiwan (4–7%), while the contributions from North Korea and Mongolia together were less than 3% of the total. The per capita SF6 emissions are highest in South Korea and Taiwan, while the per capita emissions for China, North Korea and Japan are close to global average. During the period 2006–2012, emissions from China and from South Korea increased, while emissions from Taiwan and Japan decreased overall.

Carbon tetrachloride (CCl 4 ) is an ozone-depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl 4 emissions from the eastern part of China did not decline between 2009 and 2016. This finding is in contrast to a recent bottom-up estimate, which predicted a significant decrease in emissions after the introduction of production controls. We find eastern Asian emissions of CCl 4 to be 16 (9-24) Gg/year on average between 2009 and 2016, with the primary source regions being in eastern China. The spatial distribution of emissions that we derive suggests that the source distribution of CCl 4 in China changed during the 8-year study period, indicating a new source or sources of emissions from China's Shandong province after 2012. Plain Language Summary Carbon tetrachloride is one of several man-made gases that contributeto the depletion of the ozone layer high in the atmosphere. Because of this, restrictions were introduced on the use of this ozone-depleting substance, with the expectation that production should by now be close to 0. However, the slower than expected rate of decline of carbon tetrachloride in the atmosphere shows this is not the case, and a large portion of global emissions are unaccounted for. In this study we use atmospheric measurements of carbon tetrachloride from a site in East Asia to identify the magnitude and location of emissions from this region between 2009 and 2016. We find that there are significant ongoing emissions from eastern China and that these account for a large part of the missing emissions from global estimates. The presence of continued sources of this important ozone-depleting substance indicates that more could be done to speed up the recovery of the ozone layer.

Abstract. High frequency, in situ observations from 11 globally distributed sites for the period 1994-2014 and archived air measurements dating from 1978 onward have been used to determine the global growth rate of 1,1-difluoroethane (HFC-152a, CH 3 CHF 2 ). These observations have been combined with a range of atmospheric transport models to derive global emission estimates in a topdown approach.