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O'Doherty, S, Rigby M, Muhle J, Ivy DJ, Miller BR, Young D, Simmonds PG, Reimann S, Vollmer MK, Krummel PB, Fraser PJ, Steele LP, Dunse B, Salameh PK, Harth CM, Arnold T, Weiss RF, Kim J, Park S, Li S, Lunder C, Hermansen O, Schmidbauer N, Zhou LX, Yao B, Wang RHJ, Manning AJ, Prinn RG.  2014.  Global emissions of HFC-143a (CH3CF3) and HFC-32 (CH2F2) from in situ and air archive atmospheric observations. Atmospheric Chemistry and Physics. 14:9249-9258.   10.5194/acp-14-9249-2014   AbstractWebsite

High-frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE), for the period 2003 to 2012, combined with archive flask measurements dating back to 1977, have been used to capture the rapid growth of HFC-143a (CH3CF3) and HFC-32 (CH2F2) mole fractions and emissions into the atmosphere. Here we report the first in situ global measurements of these two gases. HFC-143a and HFC-32 are the third and sixth most abundant hydrofluorocarbons (HFCs) respectively and they currently make an appreciable contribution to the HFCs in terms of atmospheric radiative forcing (1.7 +/- 0.04 and 0.7 +/- 0.02 mW m(-2) in 2012 respectively). In 2012 the global average mole fraction of HFC-143a was 13.4 +/- 0.3 ppt (1 sigma) in the lower troposphere and its growth rate was 1.4 +/- 0.04 ppt yr(-1); HFC-32 had a global mean mole fraction of 6.2 +/- 0.2 ppt and a growth rate of 1.1 +/- 0.04 ppt yr(-1) in 2012. The extensive observations presented in this work have been combined with an atmospheric transport model to simulate global atmospheric abundances and derive global emission estimates. It is estimated that 23 +/- 3 Gg yr(-1) of HFC-143a and 21 +/- 11 Gg yr(-1) of HFC-32 were emitted globally in 2012, and the emission rates are estimated to be increasing by 7 +/- 5% yr(-1) for HFC-143a and 14 +/- 11% yr(-1) for HFC-32.

Thompson, RL, Ishijima K, Saikawa E, Corazza M, Karstens U, Patra PK, Bergamaschi P, Chevallier F, Dlugokencky E, Prinn RG, Weiss RF, O'Doherty S, Fraser PJ, Steele LP, Krummel PB, Vermeulen A, Tohjima Y, Jordan A, Haszpra L, Steinbacher M, Van der Laan S, Aalto T, Meinhardt F, Popa ME, Moncrieff J, Bousquet P.  2014.  TransCom N2O model inter-comparison - Part 2: Atmospheric inversion estimates of N2O emissions. Atmospheric Chemistry and Physics. 14:6177-6194.   10.5194/acp-14-6177-2014   AbstractWebsite

This study examines N2O emission estimates from five different atmospheric inversion frameworks based on chemistry transport models (CTMs). The five frameworks differ in the choice of CTM, meteorological data, prior uncertainties and inversion method but use the same prior emissions and observation data set. The posterior modelled atmospheric N2O mole fractions are compared to observations to assess the performance of the inversions and to help diagnose problems in the modelled transport. Additionally, the mean emissions for 2006 to 2008 are compared in terms of the spatial distribution and seasonality. Overall, there is a good agreement among the inversions for the mean global total emission, which ranges from 16.1 to 18.7 TgN yr(-1) and is consistent with previous estimates. Ocean emissions represent between 31 and 38% of the global total compared to widely varying previous estimates of 24 to 38%. Emissions from the northern mid- to high latitudes are likely to be more important, with a consistent shift in emissions from the tropics and subtropics to the mid- to high latitudes in the Northern Hemisphere; the emission ratio for 0-30A degrees N to 30-90A degrees N ranges from 1.5 to 1.9 compared with 2.9 to 3.0 in previous estimates. The largest discrepancies across inversions are seen for the regions of South and East Asia and for tropical and South America owing to the poor observational constraint for these areas and to considerable differences in the modelled transport, especially inter-hemispheric exchange rates and tropical convective mixing. Estimates of the seasonal cycle in N2O emissions are also sensitive to errors in modelled stratosphere-to-troposphere transport in the tropics and southern extratropics. Overall, the results show a convergence in the global and regional emissions compared to previous independent studies.

Rigby, M, Prinn RG, O'Doherty S, Miller BR, Ivy D, Muhle J, Harth CM, Salameh PK, Arnold T, Weiss RF, Krummel PB, Steele LP, Fraser PJ, Young D, Simmonds PG.  2014.  Recent and future trends in synthetic greenhouse gas radiative forcing. Geophysical Research Letters. 41:2623-2630.   10.1002/2013gl059099   AbstractWebsite

Atmospheric measurements show that emissions of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons are now the primary drivers of the positive growth in synthetic greenhouse gas (SGHG) radiative forcing. We infer recent SGHG emissions and examine the impact of future emissions scenarios, with a particular focus on proposals to reduce HFC use under the Montreal Protocol. If these proposals are implemented, overall SGHG radiative forcing could peak at around 355mWm(-2) in 2020, before declining by approximately 26% by 2050, despite continued growth of fully fluorinated greenhouse gas emissions. Compared to no HFC policy projections, this amounts to a reduction in radiative forcing of between 50 and 240mWm(-2) by 2050 or a cumulative emissions saving equivalent to 0.5 to 2.8years of CO2 emissions at current levels. However, more complete reporting of global HFC emissions is required, as less than half of global emissions are currently accounted for.

Thompson, RL, Patra PK, Ishijima K, Saikawa E, Corazza M, Karstens U, Wilson C, Bergamaschi P, Dlugokencky E, Sweeney C, Prinn RG, Weiss RF, O'Doherty S, Fraser PJ, Steele LP, Krummel PB, Saunois M, Chipperfield M, Bousquet P.  2014.  TransCom N2O model inter-comparison - Part 1: Assessing the influence of transport and surface fluxes on tropospheric N2O variability. Atmospheric Chemistry and Physics. 14:4349-4368.   10.5194/acp-14-4349-2014   AbstractWebsite

We present a comparison of chemistry-transport models (TransCom-N2O) to examine the importance of atmospheric transport and surface fluxes on the variability of N2O mixing ratios in the troposphere. Six different models and two model variants participated in the inter-comparison and simulations were made for the period 2006 to 2009. In addition to N2O, simulations of CFC-12 and SF6 were made by a subset of four of the models to provide information on the models' proficiency in stratosphere-troposphere exchange (STE) and meridional transport, respectively. The same prior emissions were used by all models to restrict differences among models to transport and chemistry alone. Four different N2O flux scenarios totalling between 14 and 17 TgN yr(-1) (for 2005) globally were also compared. The modelled N2O mixing ratios were assessed against observations from in situ stations, discrete air sampling networks and aircraft. All models adequately captured the large-scale patterns of N2O and the vertical gradient from the troposphere to the stratosphere and most models also adequately captured the N2O tropospheric growth rate. However, all models underestimated the inter-hemispheric N2O gradient by at least 0.33 parts per billion (ppb), equivalent to 1.5 TgN, which, even after accounting for an overestimate of emissions in the Southern Ocean of circa 1.0 TgN, points to a likely underestimate of the Northern Hemisphere source by up to 0.5 TgN and/or an overestimate of STE in the Northern Hemisphere. Comparison with aircraft data reveal that the models over-estimate the amplitude of the N2O seasonal cycle at Hawaii (21 degrees N, 158 degrees W) below circa 6000 m, suggesting an overestimate of the importance of stratosphere to troposphere transport in the lower troposphere at this latitude. In the Northern Hemisphere, most of the models that provided CFC-12 simulations captured the phase of the CFC-12, seasonal cycle, indicating a reasonable representation of the timing of STE. However, for N2O all models simulated a too early minimum by 2 to 3 months owing to errors in the seasonal cycle in the prior soil emissions, which was not adequately represented by the terrestrial biosphere model. In the Southern Hemisphere, most models failed to capture the N2O and CFC-12 seasonality at Cape Grim, Tasmania, and all failed at the South Pole, whereas for SF6, all models could capture the seasonality at all sites, suggesting that there are large errors in modelled vertical transport in high southern latitudes.

Arnold, T, Ivy DJ, Harth CM, Vollmer MK, Muhle J, Salameh PK, Steele LP, Krummel PB, Wang RHJ, Young D, Lunder CR, Hermansen O, Rhee TS, Kim J, Reimann S, O'Doherty S, Fraser PJ, Simmonds PG, Prinn RG, Weiss RF.  2014.  HFC-43-10mee atmospheric abundances and global emission estimates. Geophysical Research Letters. 41:2228-2235.   10.1002/2013gl059143   AbstractWebsite

We report in situ atmospheric measurements of hydrofluorocarbon HFC-43-10mee (C5H2F10; 1,1,1,2,2,3,4,5,5,5-decafluoropentane) from seven observatories at various latitudes, together with measurements of archived air samples and recent Antarctic flask air samples. The global mean tropospheric abundance was 0.210.05ppt (parts per trillion, dry air mole fraction) in 2012, rising from 0.040.03ppt in 2000. We combine the measurements with a model and an inverse method to estimate rising global emissionsfrom 0.430.34Ggyr(-1) in 2000 to 1.130.31Ggyr(-1) in 2012 (similar to 1.9TgCO(2)-eqyr(-1) based on a 100year global warming potential of 1660). HFC-43-10meea cleaning solvent used in the electronics industryis currently a minor contributor to global radiative forcing relative to total HFCs; however, our calculated emissions highlight a significant difference from the available reported figures and projected estimates.

Thompson, RL, Chevallier F, Crotwell AM, Dutton G, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, Nakazawa T, Krummel PB, Steele LP, Fraser P, O'Doherty S, Ishijima K, Aoki S.  2014.  Nitrous oxide emissions 1999 to 2009 from a global atmospheric inversion. Atmospheric Chemistry and Physics. 14:1801-1817.   10.5194/acp-14-1801-2014   AbstractWebsite

N2O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 degrees longitude x 2.5 degrees latitude) and at monthly time resolution. Over the 11-year period, the global total N2O source varied from 17.5 to 20.1 Tg a(-1) N. Tropical and subtropical land regions were found to consistently have the highest N2O emissions, in particular in South Asia (20 +/- 3% of global total), South America (13 +/- 4 %) and Africa (19 +/- 3 %), while emissions from temperate regions were smaller: Europe (6 +/- 1 %) and North America (7 +/- 2 %). A significant multi-annual trend in N2O emissions (0.045 Tg a(-2) N) from South Asia was found and confirms inventory estimates of this trend. Considerable interannual variability in the global N2O source was observed (0.8 Tg a(-1) N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a(-1) N, 1 SD) and Africa (0.3 Tg a(-1) N, 1 SD). Notable variability was also found for N2O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a(-1) N, 1 SD, respectively). Interannual variability in the N2O source shows some correlation with the El Nino-Southern Oscillation (ENSO), where El Nino conditions are associated with lower N2O fluxes from soils and from the ocean and vice versa for La Nina conditions.

Vollmer, MK, Miller BR, Rigby M, Reimann S, Muhle J, Krummel PB, O'Doherty S, Kim J, Rhee TS, Weiss RF, Fraser PJ, Simmonds PG, Salameh PK, Harth CM, Wang RHJ, Steele LP, Young D, Lunder CR, Hermansen O, Ivy D, Arnold T, Schmidbauer N, Kim KR, Greally BR, Hill M, Leist M, Wenger A, Prinn RG.  2011.  Atmospheric histories and global emissions of the anthropogenic hydrofluorocarbons HFC-365mfc, HFC-245fa, HFC-227ea, and HFC-236fa. Journal of Geophysical Research-Atmospheres. 116   10.1029/2010jd015309   AbstractWebsite

We report on ground-based atmospheric measurements and emission estimates of the four anthropogenic hydrofluorocarbons (HFCs) HFC-365mfc (CH(3)CF(2)CH(2)CF(3), 1,1,1,3,3-pentafluorobutane), HFC-245fa (CHF(2)CH(2)CF(3), 1,1,1,3,3-pentafluoropropane), HFC-227ea (CF(3)CHFCF(3), 1,1,1,2,3,3,3-heptafluoropropane), and HFC-236fa (CF(3)CH(2)CF(3), 1,1,1,3,3,3-hexafluoropropane). In situ measurements are from the global monitoring sites of the Advanced Global Atmospheric Gases Experiment (AGAGE), the System for Observations of Halogenated Greenhouse Gases in Europe (SOGE), and Gosan (South Korea). We include the first halocarbon flask sample measurements from the Antarctic research stations King Sejong and Troll. We also present measurements of archived air samples from both hemispheres back to the 1970s. We use a two-dimensional atmospheric transport model to simulate global atmospheric abundances and to estimate global emissions. HFC-365mfc and HFC-245fa first appeared in the atmosphere only similar to 1 decade ago; they have grown rapidly to globally averaged dry air mole fractions of 0.53 ppt (in parts per trillion, 10(-12)) and 1.1 ppt, respectively, by the end of 2010. In contrast, HFC-227ea first appeared in the global atmosphere in the 1980s and has since grown to similar to 0.58 ppt. We report the first measurements of HFC-236fa in the atmosphere. This long-lived compound was present in the atmosphere at only 0.074 ppt in 2010. All four substances exhibit yearly growth rates of >8% yr(-1) at the end of 2010. We find rapidly increasing emissions for the foam-blowing compounds HFC-365mfc and HFC-245fa starting in similar to 2002. After peaking in 2006 (HFC-365mfc: 3.2 kt yr(-1), HFC-245fa: 6.5 kt yr(-1)), emissions began to decline. Our results for these two compounds suggest that recent estimates from long-term projections (to the late 21st century) have strongly overestimated emissions for the early years of the projections (similar to 2005-2010). Global HFC-227ea and HFC-236fa emissions have grown to average values of 2.4 kt yr(-1) and 0.18 kt y(r-)1 over the 2008-2010 period, respectively.

Xiao, X, Prinn RG, Fraser PJ, Weiss RF, Simmonds PG, O'Doherty S, Miller BR, Salameh PK, Harth CM, Krummel PB, Golombek A, Porter LW, Butler JH, Elkins JW, Dutton GS, Hall BD, Steele LP, Wang RHJ, Cunnold DM.  2010.  Atmospheric three-dimensional inverse modeling of regional industrial emissions and global oceanic uptake of carbon tetrachloride. Atmospheric Chemistry and Physics. 10:10421-10434.   10.5194/acp-10-10421-2010   AbstractWebsite

Carbon tetrachloride (CCl(4)) has substantial stratospheric ozone depletion potential and its consumption is controlled under the Montreal Protocol and its amendments. We implement a Kalman filter using atmospheric CCl(4) measurements and a 3-dimensional chemical transport model to estimate the interannual regional industrial emissions and seasonal global oceanic uptake of CCl(4) for the period of 1996-2004. The Model of Atmospheric Transport and Chemistry (MATCH), driven by offline National Center for Environmental Prediction (NCEP) reanalysis meteorological fields, is used to simulate CCl(4) mole fractions and calculate their sensitivities to regional sources and sinks using a finite difference approach. High frequency observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Earth System Research Laboratory (ESRL) of the National Oceanic and Atmospheric Administration (NOAA) and low frequency flask observations are together used to constrain the source and sink magnitudes, estimated as factors that multiply the a priori fluxes. Although industry data imply that the global industrial emissions were substantially declining with large interannual variations, the optimized results show only small interannual variations and a small decreasing trend. The global surface CCl(4) mole fractions were declining in this period because the CCl(4) oceanic and stratospheric sinks exceeded the industrial emissions. Compared to the a priori values, the inversion results indicate substantial increases in industrial emissions originating from the South Asian/Indian and Southeast Asian regions, and significant decreases in emissions from the European and North American regions.

Muhle, J, Huang J, Weiss RF, Prinn RG, Miller BR, Salameh PK, Harth CM, Fraser PJ, Porter LW, Greally BR, O'Doherty S, Simmonds PG.  2009.  Sulfuryl fluoride in the global atmosphere. Journal of Geophysical Research-Atmospheres. 114   10.1029/2008jd011162   AbstractWebsite

The first calibrated high-frequency, high-precision, in situ atmospheric and archived air measurements of the fumigant sulfuryl fluoride (SO(2)F(2)) have been made as part of the Advanced Global Atmospheric Gas Experiment (AGAGE) program. The global tropospheric background concentration of SO(2)F(2) has increased by 5 +/- 1% per year from similar to 0.3 ppt (parts per trillion, dry air mol fraction) in 1978 to similar to 1.35 ppt in May 2007 in the Southern Hemisphere, and from similar to 1.08 ppt in 1999 to similar to 1.53 ppt in May 2007 in the Northern Hemisphere. The SO(2)F(2) interhemispheric concentration ratio was 1.13 +/- 0.02 from 1999 to 2007. Two-dimensional 12-box model inversions yield global total and global oceanic uptake atmospheric lifetimes of 36 +/- 11 and 40 +/- 13 years, respectively, with hydrolysis in the ocean being the dominant sink, in good agreement with 35 +/- 14 years from a simple oceanic uptake calculation using transfer velocity and solubility. Modeled SO2F2 emissions rose from similar to 0.6 Gg/a in 1978 to similar to 1.9 Gg/a in 2007, but estimated industrial production exceeds these modeled emissions by an average of similar to 50%. This discrepancy cannot be explained with a hypothetical land sink in the model, suggesting that only similar to 2/3 of the manufactured SO(2)F(2) is actually emitted into the atmosphere and that similar to 1/3 may be destroyed during fumigation. With mean SO(2)F(2) tropospheric mixing ratios of similar to 1.4 ppt, its radiative forcing is small and it is probably an insignificant sulfur source to the stratosphere. However, with a high global warming potential similar to CFC-11, and likely increases in its future use, continued atmospheric monitoring of SO(2)F(2) is warranted.

Alexander, B, Vollmer MK, Jackson T, Weiss RF, Thiemens MH.  2001.  Stratospheric CO2 isotopic anomalies and SF6 and CFC tracer concentrations in the Arctic polar vortex. Geophysical Research Letters. 28:4103-4106.   10.1029/2001gl013692   AbstractWebsite

Isotopic measurements (delta O-17 and delta O-18) Of CO2 along with concentration measurements of SF6, CC1(3)F (CFC-11), CC1(2)F(2) (CFC-12) and CC1(2)FCC1F(2) (CFC-113) in stratospheric samples collected within the Arctic polar vortex are reported. These are the first simultaneous measurements of the concentration of fluorinated compounds and the complete oxygen isotopic composition Of CO2 in the middle atmosphere. A mass-independent anomaly in the oxygen isotopic composition Of CO2 is observed that arises from isotopic exchange with stratospheric O(D-1) derived from O-3 photolysis. The data exhibit a strong anti-correlation between the Delta O-17 (the degree of the mass-independent anomaly) and molecular tracer concentrations. The potential ability of tl-ris isotopic proxy to trace mesospheric and stratospheric transport is discussed.