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McNorton, J, Chipperfield MP, Gloor M, Wilson C, Feng WH, Hayman GD, Rigby M, Krummel PB, O'Doherty S, Prinn RG, Weiss RF, Young D, Dlugokencky E, Montzka SA.  2016.  Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006. Atmospheric Chemistry and Physics. 16:7943-7956.   10.5194/acp-16-7943-2016   AbstractWebsite

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 6.0aEuro-ppbaEuro-yr(-1), but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6aEuro-ppbaEuro-yr(-1). From 2007 to 2009 the growth rate again increased to 4.9aEuro-ppbaEuro-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.

Meinshausen, M, Vogel E, Nauels A, Lorbacher K, Meinshausen N, Etheridge DM, Fraser PJ, Montzka SA, Rayner PJ, Trudinger CM, Krummel PB, Beyerle U, Canadell JG, Daniel JS, Enting IG, Law RM, Lunder CR, O'Doherty S, Prinn RG, Reimann S, Rubino M, Velders GJM, Vollmer MK, Wang RHJ, Weiss R.  2017.  Historical greenhouse gas concentrations for climate modelling (CMIP6). Geoscientific Model Development. 10:2057-2116.   10.5194/gmd-10-2057-2017   AbstractWebsite

Atmospheric greenhouse gas (GHG) concentrations are at unprecedented, record-high levels compared to the last 800 000 years. Those elevated GHG concentrations warm the planet and - partially offset by net cooling effects by aerosols - are largely responsible for the observed warming over the past 150 years. An accurate representation of GHG concentrations is hence important to understand and model recent climate change. So far, community efforts to create composite datasets of GHG concentrations with seasonal and latitudinal information have focused on marine boundary layer conditions and recent trends since the 1980s. Here, we provide consolidated datasets of historical atmospheric concentrations (mole fractions) of 43 GHGs to be used in the Climate Model Intercomparison Project Phase 6 (CMIP6) experiments. The presented datasets are based on AGAGE and NOAA networks, firn and ice core data, and archived air data, and a large set of published studies. In contrast to previous intercomparisons, the new datasets are latitudinally resolved and include seasonality. We focus on the period 1850-2014 for historical CMIP6 runs, but data are also provided for the last 2000 years. Weprovide consolidated datasets in various spatiotemporal resolutions for carbon dioxide (CO2), mcthanc (CH4) and nitrous oxide (N2O), as well as 40 other GHGs, namely 17 ozone-depleting substances, 11 hydrofluorocarbons (HFCs), 9 perfluorocarbons (PFCs), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3) and sulfuryl fluoride (SO2F2). In addition we provide three equivalence species that aggregate concentrations of GHGs other than CO2, CH4 and N2O, weighted by their radiative forcing efficiencies. For the year 1850, which is used for pre-industrial control runs, we estimate annual global-mean surface concentrations of CO2 at 284.3 ppm, CH4 at 808.2 ppb and N2O at 273.0 ppb. The data are available at While the minimum CMIP6 recommendation is to use the global-and annual-mean time series, modelling groups can also choose our monthly and latitudinally resolved concentrations, which imply a stronger radiative forcing in the Northern Hemisphere winter (due to the latitudinal gradient and seasonality).

Mensch, M, Bayer R, Bullister JL, Schlosser P, Weiss RF.  1996.  The Distribution of Tritium and CFCs in the Weddell Sea during the mid-1980s. Progress in Oceanography. 38:377-415.   10.1016/s0079-6611(97)00007-4   AbstractWebsite

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea. Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the FilchnerRonne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddeil Sea Bottom Water (theta <= 0.7 degrees C) and Weddell Sea Deep Water (-0.7 degrees C <= theta <= 0 degrees C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (theta = -1.0 degrees C) and a formation rate of at least 11Sv for Antarctic Bottom Water (theta = -0.5 degrees C). (C) 1997 Elsevier Science Ltd

Miller, BR, Rigby M, Kuijpers LJM, Krummel PB, Steele LP, Leist M, Fraser PJ, McCulloch A, Harth C, Salameh P, Muhle J, Weiss RF, Prinn RG, Wang RHJ, O'Doherty S, Greally BR, Simmonds PG.  2010.  HFC-23 (CHF3) emission trend response to HCFC-22 (CHClF2) production and recent HFC-23 emission abatement measures. Atmospheric Chemistry and Physics. 10:7875-7890.   10.5194/acp-10-7875-2010   AbstractWebsite

HFC-23 (also known as CHF(3), fluoroform or trifluoromethane) is a potent greenhouse gas (GHG), with a global warming potential (GWP) of 14 800 for a 100-year time horizon. It is an unavoidable by-product of HCFC-22 (CHClF(2), chlorodifluoromethane) production. HCFC-22, an ozone depleting substance (ODS), is used extensively in commercial refrigeration and air conditioning, in the extruded polystyrene (XPS) foam industries (dispersive applications) and also as a feedstock in fluoropolymer manufacture (a non-dispersive use). Aside from small markets in specialty uses, HFC-23 has historically been considered a waste gas that was, and often still is, simply vented to the atmosphere. Efforts have been made in the past two decades to reduce HFC-23 emissions, including destruction (incineration) in facilities in developing countries under the United Nations Framework Convention on Climate Change's (UNFCCC) Clean Development Mechanism (CDM), and by process optimization and/or voluntary incineration by most producers in developed countries. We present observations of lower-tropospheric mole fractions of HFC-23 measured by 'Medusa' GC/MSD instruments from ambient air sampled in situ at the Advanced Global Atmospheric Gases Experiment (AGAGE) network of five remote sites (2007-2009) and in Cape Grim air archive (CGAA) samples (1978-2009) from Tasmania, Australia. These observations are used with the AGAGE 2-D atmospheric 12-box model and an inverse method to produce model mole fractions and a 'top-down' HFC-23 emission history. The model 2009 annual mean global lower-tropospheric background abundance is 22.6 (+/- 0.2) pmol mol(-1). The derived HFC-23 emissions show a 'plateau' during 1997-2003, followed by a rapid similar to 50% increase to a peak of 15.0 (+1.3/-1.2) Gg/yr in 2006. Following this peak, emissions of HFC-23 declined rapidly to 8.6 (+0.9/-1.0) Gg/yr in 2009, the lowest annual emission of the past 15 years. We derive a 1990-2008 'bottom-up' HFC-23 emission history using data from the United Nations Environment Programme and the UNFCCC. Comparison with the top-down HFC-23 emission history shows agreement within the stated uncertainties. In the 1990s, HFC-23 emissions from developed countries dominated all other sources, then began to decline and eventually became fairly constant during 2003-2008. By this point, with developed countries' emissions essentially at a plateau, the major factor controlling the annual dynamics of global HFC-23 emissions became the historical rise of developing countries' HCFC-22 dispersive use production, which peaked in 2007. Thereafter in 2007-2009, incineration through CDM projects became a larger factor, reducing global HFC-23 emissions despite rapidly rising HCFC-22 feedstock production in developing countries.

Miller, BR, Weiss RF, Salameh PK, Tanhua T, Greally BR, Muhle J, Simmonds PG.  2008.  Medusa: A sample preconcentration and GC/MS detector system for in situ measurements of atmospheric trace halocarbons, hydrocarbons, and sulfur compounds. Analytical Chemistry. 80:1536-1545.   10.1021/ac702084k   AbstractWebsite

Significant changes have occurred in the anthropogenic emissions of many compounds related to the Kyoto and Montreal Protocols within the past 20 years and many of their atmospheric abundances have responded dramatically. Additionally, there are a number of related natural compounds with underdetermined source or sink budgets. A new instrument, Medusa, was developed to make the high frequency in situ measurements required for the determination of the atmospheric lifetimes and emissions of these compounds. This automated system measures a wide range of halocarbons, hydrocarbons, and sulfur compounds involved in ozone depletion and/or climate forcing, from the very volatile perfluorocarbons (PFCs, e.g., CF(4) and CF(3)CF(3)) and hydrofluorocarbons (HFCs, e.g., CH(3)CF(3)) to the higher-boiling point solvents (such as CH(3)CCl(3) and CCl(2)= CCl(2)) and CHBr(3). A network of Medusa systems worldwide provides 12 in situ ambient air measurements per day of more than 38 compounds of part per trillion mole fractions and precisions up to 0.1% RSD at the five remote field stations operated by the Advanced Global Atmospheric Gases Experiment (AGAGE). Ihis custom system couples gas chromatography/mass spectrometry (GC/MSD) with a novel scheme for cryogen-free low-temperature preconcentration (-165 degrees C) of analytes from 2 L samples in a two-trap process using HayeSep D adsorbent.

Miller, BR, Huang J, Weiss RF, Prinn RG, Fraser PJ.  1998.  Atmospheric trend and lifetime of chlorodifluoromethane (HCFC-22) and the global tropospheric OH concentration. Journal of Geophysical Research-Atmospheres. 103:13237-13248.   10.1029/98jd00771   AbstractWebsite

Concentrations of CHClF2 (HCFC-22) in clean background air collected at Cape Grim, Tasmania, over the period 1978-1996, and at La Jolla, California, over the period 1992-1997, have been measured by oxygen-doped electron capture detection gas chromatography. The mid-1996 dry-air mole fractions and trends were 116.7 parts per trillion (ppt) and 6.0 ppt yr(-1) in Cape Grim and 132.4 ppt and 5.5 ppt yr(-1) in California: respectively. These observations, together with estimates of industrial emissions, have been fitted to a two-dimensional global atmospheric model by an optimal estimation inversion technique to yield estimated tropospheric and total atmospheric Lifetimes for chemical destruction of CHClF2 of 9.1(-2.8)(+4.4) years and 10.0(-3.0)(+4.4) years, respectively. These lifetimes Correspond to a temperature- and density-weighed global tropospheric OH abundance of 11.0(-3.6)(+5.0) x 10(5) radical cm(-3), which is in statistical agreement with our recent more accurate estimate of OH abundance based on measurements of CH3CCl3. Our analysis suggests that, compared to current industrial estimates, southern hemisphere emissions are higher, global emissions are larger in earlier years and smaller in later years, and, finally, production by nonreporting companies is less.

Min, DH, Bullister JL, Weiss RF.  2000.  Constant ventilation age of thermocline water in the eastern subtropical North Pacific Ocean from chlorofluorocarbon measurements over a 12-year period. Geophysical Research Letters. 27:3909-3912.   10.1029/1999gl011318   AbstractWebsite

Northeastern Pacific chlorofluorocarbon (CFC) data collected between 1982 and 1994 near Geochemical Ocean Sections Study (GEOSECS) station 1 (28.5 degreesN, 122.5 degreesW) record decadal timescale ventilation processes of the subtropical thermocline in this region. The CFC-12 concentration age field versus potential density has been remarkably constant over the 12-year period, although CFC concentrations in the upper kilometer of the water column have increased with time. Results from a simple one-dimensional advection-diffusion model are consistent with an advection velocity of ca. 0.8-0.9 cm s(-1) from the source area. The influence of the 1982-83 El Nino is noticeable in the 1983 observations. While the main stream of subarctic source water al,pears to spread southward at a constant rate, during El Nino years the influence of comparatively CFC-free tropical thermocline waters is enhanced in this region, leading to reduced vertical inventories of CFCs, but without changing the apparent CFC ages as functions of potential density. Apparent oxygen utilization rates decrease with increasing CFC age, and also appear not to have changed significantly ol er the 12-year measurement period.

Min, DH, Bullister JL, Weiss RF.  2002.  Anomalous chlorofluorocarbons in the Southern California Borderland Basins. Geophysical Research Letters. 29   10.1029/2002gl015408   AbstractWebsite

During the past two decades, unexpectedly high concentrations of chlorofluorocarbons (CFCs) have been observed in the bottom waters of the Southern California Borderland Basins (SCBB), with relatively constant spatial distribution patterns. In contrast to offshore waters in this region, CFC concentrations below the oxygen minimum layer (OML) in the deep SCBB increase with depth. The uniformity of the bottom-enhanced CFC signals and the near-zero levels of tritium suggest that this feature is likely maintained by release of CFCs from sediments and vertical mixing, and not by dumped CFC-bearing materials or an intrusion of recently ventilated waters. We hypothesize that CFC scavenging processes, either on particulate organic matter or hydrocarbon residues from the adjacent natural seeps, occur in these high-productivity near-surface coastal waters. The subsequent release of CFCs at the bottom boundary layer during the degradation of particulate material may cause the anomalous CFC distributions in the SCBB.

Montzka, SA, Fraser PJ, Butler JH, Connell PS, Cunnold DM, Daniel JS, Derwent RG, Lal S, McCulloch A, Oram D, Reeves CE, Sanhueza E, Steele LP, Velders GJM, Weiss RF, Zander R.  2003.  Controlled substances and other source gases. Scientific assessment of ozone depletion, 2002 (World Meteorological Organization, Global Ozone Research and Monitoring Project, Report 47). :83., Washington, DC: National Oceanic and Atmospheric Administration Abstract
Muhle, J, Lueker TJ, Su Y, Miller BR, Prather KA, Weiss RF.  2007.  Trace gas and particulate emissions from the 2003 southern California wildfires. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007350   AbstractWebsite

In October 2003, thirteen major wildfires in southern California burned more than 300,000 hectares of mainly chaparral biome. High-precision in situ trace gas and particle measurements of the wildfire plumes in La Jolla, California, showed a high degree of correlation among carbon dioxide (CO(2)), methane (CH(4)), nonmethane hydrocarbons, and methyl halide mixing ratios, as well as with particle number concentrations (10-300 nm and 500-2500 nm aerodynamic diameter). Aerosol time-of-flight mass spectrometry of individual aerosol particles (50-2500 nm range) showed that 70-85% had typical biomass burning signatures (levoglucosan coupled with potassium). Only 5-18% of particles in the 50 - 300 nm range had vehicle signatures. Molar trace gas enhancement ratios (ERs) versus ethane and CO(2) were calculated and showed a narrow age distribution, consistent with the short distance from the wildfires. ERs for N(2)O and CH(3)CCl(3) versus CO(2) were determined, but correlations were poor. No significant CH(2)Cl(2) or CHCl(3) emissions were detected. CO2 emissions from the nearby Cedar fire were estimated both with a simple Lagrangian atmospheric transport model and a burned area approach and extrapolated to 11 Tg CO(2) for the total burned area in southern California. Total CO(2), CH(4), C(2)-hydrocarbons, benzene, toluene, methyl chloride, methyl iodide, and PM(2.5) emissions were similar to 0.2-3.5% of yearly global extratropical forest fire emissions and more than 28% of CH(4), C(6)H(6), and PM(2.5) 2003 San Diego and South Coast Air Basins anthropogenic emissions. Particle distributions and single particle chemistry are discussed. PM(2.5) considerably exceeded the EPA short-term exposure limit.

Muhle, J, Ganesan AL, Miller BR, Salameh PK, Harth CM, Greally BR, Rigby M, Porter LW, Steele LP, Trudinger CM, Krummel PB, O'Doherty S, Fraser PJ, Simmonds PG, Prinn RG, Weiss RF.  2010.  Perfluorocarbons in the global atmosphere: tetrafluoromethane, hexafluoroethane, and octafluoropropane. Atmospheric Chemistry and Physics. 10:5145-5164.   10.5194/acp-10-5145-2010   AbstractWebsite

We present atmospheric baseline growth rates from the 1970s to the present for the long-lived, strongly infrared-absorbing perfluorocarbons (PFCs) tetrafluoromethane (CF(4)), hexafluoroethane (C(2)F(6)), and octafluoropropane (C(3)F(8)) in both hemispheres, measured with improved accuracies (similar to 1-2%) and precisions (<0.3%, or <0.2 ppt (parts per trillion dry air mole fraction), for CF(4); <1.5%, or <0.06 ppt, for C(2)F(6); <4.5%, or <0.02 ppt, for C3F8) within the Advanced Global Atmospheric Gases Experiment (AGAGE). Pre-industrial background values of 34.7 +/- 0.2 ppt CF(4) and 0.1 +/- 0.02 ppt C(2)F(6) were measured in air extracted from Greenland ice and Antarctic firn. Anthropogenic sources are thought to be primary aluminum production (CF(4), C(2)F(6), C(3)F(8)), semiconductor production (C(2)F(6), CF(4), C(3)F(8)) and refrigeration use (C(3)F(8)). Global emissions calculated with the AGAGE 2-D 12-box model are significantly higher than most previous emission estimates. The sum of CF(4) and C(2)F(6) emissions estimated from aluminum production and non-metal production are lower than observed global top-down emissions, with gaps of similar to 6 Gg/yr CF(4) in recent years. The significant discrepancies between previous CF(4), C(2)F(6), and C(3)F(8) emission estimates and observed global top-down emissions estimated from AGAGE measurements emphasize the need for more accurate, transparent, and complete emission reporting, and for verification with atmospheric measurements to assess the emission sources of these long-lived and potent greenhouse gases, which alter the radiative budget of the atmosphere, essentially permanently, once emitted.

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.

Murphy, PP, Harrison DE, Feely RA, Takahashi T, Weiss RF, Gammon RH.  1998.  Variability of Δ pCO2 in the subarctic North Pacific. A comparison of results from four expeditions. Tellus Series B-Chemical and Physical Meteorology. 50:185-204.   10.1034/j.1600-0889.1998.t01-1-00006.x   AbstractWebsite

Time-space variability of surface seawater pCO(2) is examined over the region (150 degrees W-180 degrees, 46 degrees N-50 degrees N) of the subarctic North Pacific where large meridional gradients of temperature and nutrient concentrations exist. The data were collected during four trans-Pacific expeditions in three different years (1985-1987), but within the same 30-day period of the year (August-September). Systematic measurement differences between the four data sets are estimated as <10 mu atm. The inter-expedition comparison suggests that surface seawater pCO(2) in the study area is quite variable, with mean differences of up to 25 mu atm and local differences up to 60 mu atm. Spatial and interannual variability of surface seawater pCO(2) were found to contribute significant uncertainty to estimates of the mean Delta pCO(2) for the study area. Fluxes were calculated using Delta pCO(2) values from the four expeditions combined with gas exchange coefficients calculated from four different wind fields giving a range of -0.94 to +4.1 mmol CO2 m(-2) d(-1). The range of fluxes from the study area is scaled to a larger area of the North Pacific to address how this variability can translate into uncertainties in basin-wide carbon air-sea exchange fluxes.