No abstract

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. The growth in atmospheric methane (CH4) concentrations over the past 2 decades has shown large variability on a timescale of several years. Prior to 1999 the globally averaged CH4 concentration was increasing at a rate of 6.0 ppb yr−1, but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6 ppb yr−1. From 2007 to 2009 the growth rate again increased to 4.9 ppb yr−1. These changes in growth rate are usually ascribed to variations in CH4 emissions. We have used a 3-D global chemical transport model, driven by meteorological reanalyses and variations in global mean hydroxyl (OH) concentrations derived from CH3CCl3 observations from two independent networks, to investigate these CH4 growth variations. The model shows that between 1999 and 2006 changes in the CH4 atmospheric loss contributed significantly to the suppression in global CH4 concentrations relative to the pre-1999 trend. The largest factor in this is relatively small variations in global mean OH on a timescale of a few years, with minor contributions of atmospheric transport of CH4 to its sink region and of atmospheric temperature. Although changes in emissions may be important during the stagnation period, these results imply a smaller variation is required to explain the observed CH4 trends. The contribution of OH variations to the renewed CH4 growth after 2007 cannot be determined with data currently available.

Carbonyl sulfide (COS) and C 18 OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO 2 exchange, and both are assumed to depend on carbonic anhydrase (CA) activity and conductance along the diffusive pathway in leaves. We investigated these links using C 3 and C 4 plants, hypothesizing that the rates of COS and C 18OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C 4 and C 3 plants, COS uptake was essentially eliminated and discrimination against C The seasonal cycling of CO 2 concentration measured in the background atmosphere is often taken as evidence of the breathing of Earth and corresponds to about 10 Pg carbon. This is less than 10% of what we estimate to be the total cycling of CO 2 due to respiration and photosynthesis of the terrestrial biosphere (Beer et al., 2010). The discrepancy stems from the fact that most of the cycling CO 2 mixes in the atmosphere near the surface, and we only see the net sum of respiration and photosynthesis, which are often more or less balanced over the seasonal cycle. Modeling and measurements of CO 2 exchange by ecosystems over diurnal cycles have been used to deconvolve the primary biological processes (e.g. Desai et al., 2008). However, our confidence in these approaches disintegrates as we move to larger scales because of the increase in the internal mixing of CO 2 fluxes. Other approaches are needed to quantify the basic physiological processes at these scales.