High‐frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and System for Observation of halogenated Greenhouse gases in Europe (SOGE) networks for the period 1998 to 2008, combined with archive flask measurements dating back to 1978, have been used to capture the rapid growth of HFC‐125 (CHF2CF3) in the atmosphere. HFC‐125 is the fifth most abundant HFC, and it currently makes the third largest contribution of the HFCs to atmospheric radiative forcing. At the beginning of 2008 the global average was 5.6 ppt in the lower troposphere and the growth rate was 16% yr−1. The extensive observations have been combined with a range of modeling techniques to derive global emission estimates in a top‐down approach. It is estimated that 21 kt were emitted globally in 2007, and the emissions are estimated to have increased 15% yr−1 since 2000. These estimates agree within approximately 20% with values reported to the United Nations Framework Convention on Climate Change (UNFCCC) provided that estimated emissions from East Asia are included. Observations of regionally polluted air masses at individual AGAGE sites have been used to produce emission estimates for Europe (the EU‐15 countries), the United States, and Australia. Comparisons between these top‐down estimates and bottom‐up estimates based on reports by individual countries to the UNFCCC show a range of approximately four in the differences. This process of independent verification of emissions, and an understanding of the differences, is vital for assessing the effectiveness of international treaties, such as the Kyoto Protocol.

HCFC-22 (CHClF2, chlorodifluoromethane ) is an ozone-depleting substance (ODS) as well as a significant greenhouse gas (GHG). HCFC-22 has been used widely as a refrigerant fluid in cooling and air-conditioning equipment since the 1960s, and it has also served as a traditional substitute for some chlorofluorocarbons (CFCs) controlled under the Montreal Protocol. A low frequency record on tropospheric HCFC-22 since the late 1970s is available from measurements of the Southern Hemisphere Cape Grim Air Archive (CGAA) and a few Northern Hemisphere air samples (mostly from Trinidad Head) using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. Since the 1990s high-frequency, high-precision, in situ HCFC-22 measurements have been collected at these AGAGE stations. Since 1992, the Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected flasks on a weekly basis from remote sites across the globe and analyzed them for a suite of halocarbons including HCFC-22. Additionally, since 2006 flasks have been collected approximately daily at a number of tower sites across the US and analyzed for halocarbons and other gases at NOAA. All results show an increase in the atmospheric mole fractions of HCFC-22, and recent data show a growth rate of approximately 4% per year, resulting in an increase in the background atmospheric mole fraction by a factor of 1.7 from 1995 to 2009. Using data on HCFC-22 consumption submitted to the United Nations Environment Programme (UNEP), as well as existing bottom-up emission estimates, we first create globally-gridded a priori HCFC-22 emissions over the 15 yr since 1995. We then use the three-dimensional chemical transport model, Model for Ozone and Related Chemical Tracers version 4 (MOZART v4), and a Bayesian inverse method to estimate global as well as regional annual emissions. Our inversion indicates that the global HCFC-22 emissions have an increasing trend between 1995 and 2009. We further find a surge in HCFC-22 emissions between 2005 and 2009 from developing countries in Asia – the largest emitting region including China and India. Globally, substantial emissions continue despite production and consumption being phased out in developed countries currently

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Abstract. Biologically produced molecular hydrogen (H 2 )is characterised by a very strong depletion in deuterium. Although the biological source to the atmosphere is small compared to photochemical or combustion sources, it makes an important contribution to the global isotope budget of H 2 . Large uncertainties exist in the quantification of the individual production and degradation processes that contribute to the atmospheric budget, and isotope measurements are a tool to distinguish the contributions from the different sources. Measurements of δD from the various H 2 sources are scarce and for biologically produced H 2 only very few measurements exist.Here the first systematic study of the isotopic composition of biologically produced H 2 is presented. In a first set of experiments, we investigated δD of H 2 produced in a biogas plant, covering different treatments of biogas production. In a second set of experiments, we investigated pure cultures of several H 2 producing microorganisms such as bacteria or green algae. A Keeling plot analysis provides a robust overall source signature of δD = −712 ‰ (±13 ‰) for the samples from the biogas reactor (at 38 • C, δD H 2 O = +73.4 ‰), with a fractionation constant ε H 2 -H 2 O of −689 ‰ (±20 ‰) between H 2 and the water. The five experiments using pure culture samples from different microorganisms give a mean source signature of δD = −728 ‰ (±28 ‰), and a fractionation constant ε H 2 -H 2 O of −711 ‰ (±34 ‰) between H 2 and the water. The results confirm the massive deuterium depletion of biologically produced H 2 as was predicted by the calculation of the thermodynamic fractionation factors for hydrogen exchange between H 2 and water vapour. Systematic errors in the isotope scale are difficult to assess in the absence of international standards for δD of H 2 .As expected for a thermodynamic equilibrium, the fractionation factor is temperature dependent, but largely independent of the substrates used and the H 2 production conditions. The equilibrium fractionation coefficient is positively correlated with temperature and we measured a rate of change of 2.3 ‰ / • C between 45 • C and 60 • C, which is in general agreement with the theoretical prediction of 1.4 ‰ / • C.Our best experimental estimate for ε H 2 -H 2 O at a temperature of 20 • C is −731 ‰ (±20 ‰) for biologically produced H 2 . This value is close to the predicted value of −722 ‰, and we suggest using these values in future global H 2 isotope budget calculations and models with adjusting to regional temperatures for calculating δD values.