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.

Abstract. Molecular hydrogen (H 2 ), its isotopic signature (deuterium/hydrogen, δD), carbon monoxide (CO), and other compounds were studied in the exhaust of a passenger car engine fuelled with gasoline or methane and run under variable air-fuel ratios and operating modes. H 2 and CO concentrations were largely reduced downstream of the three-way catalytic converter (TWC) compared to levels upstream, and showed a strong dependence on the air-fuel ratio (expressed as lambda, λ). The isotopic composition of H 2 ranged from δD=−140‰ to δD = −195‰ upstream of the TWC but these values decreased to −270‰ to −370‰ after passing through the TWC. Post-TWC δD values for the fuelrich range showed a strong dependence on TWC temperature with more negative δD for lower temperatures. These effects are attributed to a rapid temperature-dependent H-D isotope equilibration between H 2 and water (H 2 O). In addition, post TWC δD in H 2 showed a strong dependence on the fraction of removed H 2 , suggesting isotopic enrichment during catalytic removal of H 2 with enrichment factors (ε) ranging from −39.8‰ to −15.5‰ depending on the operating mode. Our results imply that there may be considerable variability in real-world δD emissions from vehicle exhaust, which may mainly depend on TWC technology and exhaust temperature regime. This variability is suggestive of a δD from traffic that varies over time, by season, and by geographical location. An earlier-derived integrated pure (end-member) δD from anthropogenic activities of −270‰ (Rahn et al., 2002) Correspondence to: M. K. Vollmer (martin.vollmer@empa.ch) can be explained as a mixture of mainly vehicle emissions from cold starts and fully functional TWCs, but enhanced δD values by >50‰ are likely for regions where TWC technology is not fully implemented. Our results also suggest that a full hydrogen isotope analysis on fuel and exhaust gas may greatly aid at understanding process-level reactions in the exhaust gas, in particular in the TWC.

[1] This work reassesses the global atmospheric budget of H 2 with the TM5 model. The recent adjustment of the calibration scale for H 2 translates into a change in the tropospheric burden. Furthermore, the ECMWF Reanalysis-Interim (ERA-Interim) data from the European Centre for Medium-Range Weather Forecasts (ECMWF) used in this study show slower vertical transport than the operational data used before. Consequently, more H 2 is removed by deposition. The deposition parametrization is updated because significant deposition fluxes for snow, water, and vegetation surfaces were calculated in our previous study. Timescales of 1-2 h are asserted for the transport of H 2 through the canopies of densely vegetated regions. The global scale variability of H 2 and ıD[H 2 ] is well represented by the updated model. H 2 is slightly overestimated in the Southern Hemisphere because too little H 2 is removed by dry deposition to rainforests and savannahs. The variability in H 2 over Europe is further investigated using a high-resolution model subdomain. It is shown that discrepancies between the model and the observations are mainly caused by the finite model resolution. The tropospheric burden is estimated at 165˙8 Tg H 2 . The removal rates of H 2 by deposition and photochemical oxidation are estimated at 53˙4 and 23˙2 Tg H 2 /yr, resulting in a tropospheric lifetime of 2.2˙0.2 year.Citation: Pieterse, G., et al. (2013), Reassessing the variability in atmospheric H 2 using the two-way nested TM5 model,

The International Halocarbons in Air Comparison Experiment (IHALACE) was conducted to document relationships between calibration scales among various laboratories that measure atmospheric greenhouse and ozone depleting gases. Six stainless steel cylinders containing natural and modified natural air samples were circulated among 19 laboratories. Results from this experiment reveal relatively good agreement among commonly used calibration scales for a number of trace gases present in the unpolluted atmosphere at pmol mol⁻¹ (parts per trillion) levels, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). Some scale relationships were found to be consistent with those derived from bi-lateral experiments or from analysis of atmospheric data, while others revealed discrepancies. The transfer of calibration scales among laboratories was found to be problematic in many cases, meaning that measurements tied to a common scale may not, in fact, be compatible. These results reveal substantial improvements in calibration over previous comparisons. However there is room for improvement in communication and coordination of calibration activities with respect to the measurement of halogenated and related trace gases