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2018
Elvidge, EL, Bonisch H, Brenninkmeijer CAM, Engel A, Fraser PJ, Gallacher E, Langenfelds R, Muhle J, Oram DE, Ray EA, Ridley AR, Rockmann T, Sturges WT, Weiss RF, Laube JC.  2018.  Evaluation of stratospheric age of air from CF4, C2F6, C3F8, CHF3, HFC-125, HFC-227ea and SF6; implications for the calculations of halocarbon lifetimes, fractional release factors and ozone depletion potentials. Atmospheric Chemistry and Physics. 18:3369-3385.   10.5194/acp-18-3369-2018   AbstractWebsite

In a changing climate, potential stratospheric circulation changes require long-term monitoring. Stratospheric trace gas measurements are often used as a proxy for stratospheric circulation changes via the "mean age of air" values derived from them. In this study, we investigated five potential age of air tracers - the perfluorocarbons CF4, C2F6 and C3F8 and the hydrofluorocarbons CHF3 (HFC-23) and HFC-125 - and compare them to the traditional tracer SF6 and a (relatively) shorter-lived species, HFC-227ea. A detailed uncertainty analysis was performed on mean ages derived from these "new" tracers to allow us to confidently compare their efficacy as age tracers to the existing tracer, SF6. Our results showed that uncertainties associated with the mean age derived from these new age tracers are similar to those derived from SF6, suggesting that these alternative compounds are suitable in this respect for use as age tracers. Independent verification of the suitability of these age tracers is provided by a comparison between samples analysed at the University of East Anglia and the Scripps Institution of Oceanography. All five tracers give younger mean ages than SF6, a discrepancy that increases with increasing mean age. Our findings qualitatively support recent work that suggests that the stratospheric lifetime of SF6 is significantly less than the previous estimate of 3200 years. The impact of these younger mean ages on three policy-relevant parameters - stratospheric lifetimes, fractional release factors (FRFs) and ozone depletion potentials - is investigated in combination with a recently improved methodology to calculate FRFs. Updates to previous estimations for these parameters are provided.

Vollmer, MK, Young D, Trudinger CM, Muhle J, Henne S, Rigby M, Park S, Li S, Guillevic M, Mitrevski B, Harth CM, Miller BR, Reimann S, Yao B, Steele LP, Wyss SA, Lunder CR, Arduini J, McCulloch A, Wu S, Rhee TS, Wang RHJ, Salameh PK, Hermansen O, Hill M, Langenfelds RL, Ivy D, O'Doherty S, Krummel PB, Maione M, Etheridge DM, Zhou LX, Fraser PJ, Prinn RG, Weiss RF, Simmonds PG.  2018.  Atmospheric histories and emissions of chlorofluorocarbons CFC-13 (CClF3), Sigma CFC-114 (C2Cl2F4), and CFC-115 (C2ClF5). Atmospheric Chemistry and Physics. 18:979-1002.   10.5194/acp-18-979-2018   AbstractWebsite

Based on observations of the chlorofluorocarbons CFC-13 (chlorotrifluoromethane), Sigma CFC-114 (combined measurement of both isomers of dichlorotetrafluoroethane), and CFC-115 (chloropentafluoroethane) in atmospheric and firn samples, we reconstruct records of their tropospheric histories spanning nearly 8 decades. These compounds were measured in polar firn air samples, in ambient air archived in canisters, and in situ at the AGAGE (Advanced Global Atmospheric Gases Experiment) network and affiliated sites. Global emissions to the atmosphere are derived from these observations using an inversion based on a 12-box atmospheric transport model. For CFC-13, we provide the first comprehensive global analysis. This compound increased monotonically from its first appearance in the atmosphere in the late 1950s to a mean global abundance of 3.18 ppt (dry-air mole fraction in parts per trillion, pmol mol(-1)) in 2016. Its growth rate has decreased since the mid-1980s but has remained at a surprisingly high mean level of 0.02 ppt yr(-1) since 2000, resulting in a continuing growth of CFC-13 in the atmosphere. Sigma CFC-114 increased from its appearance in the 1950s to a maximum of 16.6 ppt in the early 2000s and has since slightly declined to 16.3 ppt in 2016. CFC-115 increased monotonically from its first appearance in the 1960s and reached a global mean mole fraction of 8.49 ppt in 2016. Growth rates of all three compounds over the past years are significantly larger than would be expected from zero emissions. Under the assumption of unchanging lifetimes and atmospheric transport patterns, we derive global emissions from our measurements, which have remained unexpectedly high in recent years: mean yearly emissions for the last decade (2007-2016) of CFC-13 are at 0.48 +/- 0.15 kt yr(-1) (> 15% of past peak emissions), of 6 CFC-114 at 1.90 +/- 0.84 kt yr(-1) (similar to 10% of peak emissions), and of CFC-115 at 0.80 +/- 0.50 kt yr(-1) (> 5% of peak emissions). Mean yearly emissions of CFC-115 for 2015-2016 are 1.14 +/- 0.50 kt yr(-1) and have doubled compared to the 2007-2010 minimum. We find CFC-13 emissions from aluminum smelters but if extrapolated to global emissions, they cannot account for the lingering global emissions determined from the atmospheric observations. We find impurities of CFC-115 in the refrigerant HFC-125 (CHF2CF3) but if extrapolated to global emissions, they can neither account for the lingering global CFC-115 emissions determined from the atmospheric observations nor for their recent increases. We also conduct regional inversions for the years 2012-2016 for the northeastern Asian area using observations from the Korean AGAGE site at Gosan and find significant emissions for Sigma CFC-114 and CFC-115, suggesting that a large fraction of their global emissions currently occur in northeastern Asia and more specifically on the Chinese mainland.

2015
Wells, KC, Millet DB, Bousserez N, Henze DK, Chaliyakunnel S, Griffis TJ, Luan Y, Dlugokencky EJ, Prinn RG, O'Doherty S, Weiss RF, Dutton GS, Elkins JW, Krummel PB, Langenfelds R, Steele LP, Kort EA, Wofsy SC, Umezawa T.  2015.  Simulation of atmospheric N2O with GEOS-Chem and its adjoint: evaluation of observational constraints. Geoscientific Model Development. 8:3179-3198.   10.5194/gmd-8-3179-2015   AbstractWebsite

We describe a new 4D-Var inversion framework for nitrous oxide (N2O) based on the GEOS-Chem chemical transport model and its adjoint, and apply it in a series of observing system simulation experiments to assess how well N2O sources and sinks can be constrained by the current global observing network. The employed measurement ensemble includes approximately weekly and quasicontinuous N2O measurements (hourly averages used) from several long-term monitoring networks, N2O measurements collected from discrete air samples onboard a commercial aircraft (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container; CARIBIC), and quasi-continuous measurements from the airborne HIAPER Pole-to-Pole Observations (HIPPO) campaigns. For a 2-year inversion, we find that the surface and HIPPO observations can accurately resolve a uniform bias in emissions during the first year; CARIBIC data provide a somewhat weaker constraint. Variable emission errors are much more difficult to resolve given the long lifetime of N2O, and major parts of the world lack significant constraints on the seasonal cycle of fluxes. Current observations can largely correct a global bias in the stratospheric sink of N2O if emissions are known, but do not provide information on the temporal and spatial distribution of the sink. However, for the more realistic scenario where source and sink are both uncertain, we find that simultaneously optimizing both would require unrealistically small errors in model transport. Regardless, a bias in the magnitude of the N2O sink would not affect the a posteriori N2O emissions for the 2-year timescale used here, given realistic initial conditions, due to the timescale required for stratosphere-troposphere exchange (STE). The same does not apply to model errors in the rate of STE itself, which we show exerts a larger influence on the tropospheric burden of N2O than does the chemical loss rate over short (< 3 year) timescales. We use a stochastic estimate of the inverse Hessian for the inversion to evaluate the spatial resolution of emission constraints provided by the observations, and find that significant, spatially explicit constraints can be achieved in locations near and immediately upwind of surface measurements and the HIPPO flight tracks; however, these are mostly confined to North America, Europe, and Australia. None of the current observing networks are able to provide significant spatial information on tropical N2O emissions. There, averaging kernels (describing the sensitivity of the inversion to emissions in each grid square) are highly smeared spatially and extend even to the midlatitudes, so that tropical emissions risk being conflated with those elsewhere. For global inversions, therefore, the current lack of constraints on the tropics also places an important limit on our ability to understand extratropical emissions. Based on the error reduction statistics from the inverse Hessian, we characterize the atmospheric distribution of unconstrained N2O, and identify regions in and downwind of South America, central Africa, and Southeast Asia where new surface or profile measurements would have the most value for reducing present uncertainty in the global N2O budget.

2014
Patra, PK, Krol MC, Montzka SA, Arnold T, Atlas EL, Lintner BR, Stephens BB, Xiang B, Elkins JW, Fraser PJ, Ghosh A, Hintsa EJ, Hurst DF, Ishijima K, Krummel PB, Miller BR, Miyazaki K, Moore FL, Muhle J, O'Doherty S, Prinn RG, Steele LP, Takigawa M, Wang HJ, Weiss RF, Wofsy SC, Young D.  2014.  Observational evidence for interhemispheric hydroxyl-radical parity. Nature. 513:219-+.   10.1038/nature13721   AbstractWebsite

The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere(1-3). The ratio of Northern Hemispheric to Southern Hemispheric (NH/SH) OH concentration is important for our understanding of emission estimates of atmospheric species such as nitrogen oxides and methane(4-6). It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4,7-10). Here we determine the NH/SH ratio of OH with the help of methyl chloroform data (a proxy for OH concentrations) and an atmospheric transport model that accurately describes interhemispheric transport and modelled emissions. We find that for the years 2004-2011 the model predicts an annual mean NH-SH gradient of methyl chloroform that is a tight linear function of the modelled NH/SH ratio in annual mean OH. We estimate a NH/SH OH ratio of 0.97 +/- 0.12 during this time period by optimizing global total emissions and mean OH abundance to fit methyl chloroform data from two surface-measurement networks and aircraft campaigns(11-13). Our findings suggest that top-down emission estimates of reactive species such as nitrogen oxides in key emitting countries in the NH that are based on a NH/SH OH ratio larger than 1 may be overestimated.

2011
Nevison, CD, Dlugokencky E, Dutton G, Elkins JW, Fraser P, Hall B, Krummel PB, Langenfelds RL, O'Doherty S, Prinn RG, Steele LP, Weiss RF.  2011.  Exploring causes of interannual variability in the seasonal cycles of tropospheric nitrous oxide. Atmospheric Chemistry and Physics. 11:3713-3730.   10.5194/acp-11-3713-2011   AbstractWebsite

Seasonal cycles in the mixing ratios of tropospheric nitrous oxide (N(2)O) are derived by detrending long-term measurements made at sites across four global surface monitoring networks. The detrended monthly data display large interannual variability, which at some sites challenges the concept of a "mean" seasonal cycle. In the Northern Hemisphere, correlations between polar winter lower stratospheric temperature and detrended N(2)O data, around the month of the seasonal minimum, provide empirical evidence for a stratospheric influence, which varies in strength from year to year and can explain much of the interannual variability in the surface seasonal cycle. Even at sites where a strong, competing, regional N(2)O source exists, such as from coastal upwelling at Trinidad Head, California, the stratospheric influence must be understood to interpret the biogeochemical signal in monthly mean data. In the Southern Hemisphere, detrended surface N(2)O monthly means are correlated with polar spring lower stratospheric temperature in months preceding the N(2)O minimum, providing empirical evidence for a coherent stratospheric influence in that hemisphere as well, in contrast to some recent atmospheric chemical transport model (ACTM) results. Correlations between the phasing of the surface N(2)O seasonal cycle in both hemispheres and both polar lower stratospheric temperature and polar vortex break-up date provide additional support for a stratospheric influence. The correlations discussed above are generally more evident in high-frequency in situ data than in data from weekly flask samples. Furthermore, the interannual variability in the N(2)O seasonal cycle is not always correlated among in situ and flask networks that share common sites, nor do the mean seasonal amplitudes always agree. The importance of abiotic influences such as the stratospheric influx and tropospheric transport on N(2)O seasonal cycles suggests that, at sites remote from local sources, surface N(2)O mixing ratio data by themselves are unlikely to provide information about seasonality in surface sources, e. g., for atmospheric inversions, unless the ACTMs employed in the inversions accurately account for these influences. An additional abioitc influence is the seasonal ingassing and outgassing of cooling and warming surface waters, which creates a thermal signal in tropospheric N(2)O that is of particular importance in the extratropical Southern Hemisphere, where it competes with the biological ocean source signal.

2010
Rigby, M, Muhle J, Miller BR, Prinn RG, Krummel PB, Steele LP, Fraser PJ, Salameh PK, Harth CM, Weiss RF, Greally BR, O'Doherty S, Simmonds PG, Vollmer MK, Reimann S, Kim J, Kim KR, Wang HJ, Olivier JGJ, Dlugokencky EJ, Dutton GS, Hall BD, Elkins JW.  2010.  History of atmospheric SF6 from 1973 to 2008. Atmospheric Chemistry and Physics. 10:10305-10320.   10.5194/acp-10-10305-2010   AbstractWebsite

We present atmospheric sulfur hexafluoride (SF(6)) mole fractions and emissions estimates from the 1970s to 2008. Measurements were made of archived air samples starting from 1973 in the Northern Hemisphere and from 1978 in the Southern Hemisphere, using the Advanced Global Atmospheric Gases Experiment (AGAGE) gas chromatographic-mass spectrometric (GC-MS) systems. These measurements were combined with modern high-frequency GC-MS and GC-electron capture detection (ECD) data from AGAGE monitoring sites, to produce a unique 35-year atmospheric record of this potent greenhouse gas. Atmospheric mole fractions were found to have increased by more than an order of magnitude between 1973 and 2008. The 2008 growth rate was the highest recorded, at 0.29 +/- 0.02 pmol mol(-1) yr(-1). A three-dimensional chemical transport model and a minimum variance Bayesian inverse method was used to estimate annual emission rates using the measurements, with a priori estimates from the Emissions Database for Global Atmospheric Research (EDGAR, version 4). Consistent with the mole fraction growth rate maximum, global emissions during 2008 were also the highest in the 1973-2008 period, reaching 7.4 +/- 0.6 Gg yr(-1) (1-sigma uncertainties) and surpassing the previous maximum in 1995. The 2008 values follow an increase in emissions of 48 +/- 20% since 2001. A second global inversion which also incorporated National Oceanic and Atmospheric Administration (NOAA) flask measurements and in situ monitoring site data agreed well with the emissions derived using AGAGE measurements alone. By estimating continent-scale emissions using all available AGAGE and NOAA surface measurements covering the period 2004-2008, with no pollution filtering, we find that it is likely that much of the global emissions rise during this five-year period originated primarily from Asian developing countries that do not report detailed, annual emissions to the United Nations Framework Convention on Climate Change (UNFCCC). We also find it likely that SF(6) emissions reported to the UNFCCC were underestimated between at least 2004 and 2005.

2007
Nevison, CD, Mahowald NM, Weiss RF, Prinn RG.  2007.  Interannual and seasonal variability in atmospheric N2O. Global Biogeochemical Cycles. 21   10.1029/2006gb002755   AbstractWebsite

The increase in atmospheric N2O observed over the last century reflects large- scale human perturbations to the global nitrogen cycle. High- precision measurements of atmospheric N2O over the last decade reveal subtle signals of interannual variability (IAV) superimposed upon the more prominent growth trend. Anthropogenic sources drive the underlying growth in N2O, but are probably too monotonic to explain most of the observed IAV. The causes of both seasonal and interannual variability in atmospheric N2O are explored on the basis of comparisons of a 1993 - 2004 atmospheric transport simulation to observations of N2O at five stations of the Advanced Global Atmospheric Gases Experiment (AGAGE). The complementary tracers chlorofluorocarbons (CFCs) 11 and 12 and SF6 also are examined. The model simulation does not include a stratospheric sink and thus isolates the effects of surface sources and tropospheric transport. Both model and observations yield correlations in seasonal and interannual variability among species, but only in a few cases are model and observed variability correlated to each other. The results suggest that tropospheric transport contributes substantially to observed variability, especially at Samoa station. However, some features of observed variability are not explained by the model simulation and appear more consistent with a stratospheric influence. At Mace Head, Ireland, N2O and CFC growth rate anomalies are weakly correlated to IAV in polar winter lower stratospheric temperature, a proxy for the strength of the mean meridional stratospheric circulation. Seasonal and interannual variability in the natural sources of N2O may also contribute to observed variability in atmospheric N2O.

Xiao, X, Prinn RG, Simmonds PG, Steele LP, Novelli PC, Huang J, Langenfelds RL, O'Doherty S, Krummel PB, Fraser PJ, Porter LW, Weiss RF, Salameh P, Wang RHJ.  2007.  Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007241   AbstractWebsite

[1] Hydrogen (H(2)), a proposed clean energy alternative, warrants detailed investigation of its global budget and future environmental impacts. The magnitudes and seasonal cycles of the major ( presumably microbial) soil sink of hydrogen have been estimated from high-frequency in situ AGAGE H(2) observations and also from more geographically extensive but low-frequency flask measurements from CSIRO and NOAA-GMD using the Kalman filter in a two-dimensional (2-D) global transport model. Hydrogen mole fractions exhibit well-defined seasonal cycles in each hemisphere with their phase difference being only about 3 months. The global production rate of H(2) is estimated to be 103 +/- 10 Tg yr(-1) with only a small estimated interannual variation. Soil uptake ( 84 +/- 8 Tg yr(-1)) represents the major loss process for H(2) and accounts for 81% of the total destruction. Strong seasonal cycles are deduced for the soil uptake of H(2). The soil sink is a maximum over the northern extratropics in summer and peaks only 2 to 3 months earlier in the Northern Hemisphere than in the Southern Hemisphere. Oxidation by tropospheric OH (18 +/- 3 Tg yr(-1)) accounts for 17% of the destruction, with the remainder due to destruction in the stratosphere. The calculated global burden is 191 +/- 29 Tg, indicating an overall atmospheric lifetime of 1.8 +/- 0.3 years. Hydrogen in the troposphere ( 149 +/- 23 Tg burden) has a lifetime of 1.4 +/- 0.2 years.

2004
Nevison, CD, Kinnison DE, Weiss RF.  2004.  Stratospheric influences on the tropospheric seasonal cycles of nitrous oxide and chlorofluorocarbons. Geophysical Research Letters. 31   10.1029/2004gl020398   AbstractWebsite

The stratospheric influence on the tropospheric seasonal cycles of N2O, CFC-11 ( CCl3F), CFC-12 (CCl2F2) and CFC-113 (CCl2FCClF2) is investigated using observations from the AGAGE global trace gas monitoring network and the results of the Whole Atmosphere Community Climate Model (WACCM). WACCM provides the basis for a number of predictions about the relative amplitudes of N2O and CFC seasonal cycles and about the relative magnitude and phasing of seasonal cycles in the northern and southern hemispheres. These predictions are generally consistent with observations, suggesting that the stratosphere exerts a coherent influence on the tropospheric seasonal cycles of trace gases whose primary sinks are in the stratosphere. This stratospheric influence may complicate efforts to validate estimated source distributions of N2O, an important greenhouse gas, in atmospheric transport model studies.

2002
Rhein, M, Fischer J, Smethie WM, Smythe-Wright D, Weiss RF, Mertens C, Min DH, Fleischmann U, Putzka A.  2002.  Labrador Sea Water: pathways, CFC inventory, and formation rates. Journal of Physical Oceanography. 32:648-665.   10.1175/1520-0485(2002)032<0648:lswpci>2.0.co;2   AbstractWebsite

In 1997, a unique hydrographic and chlorofluorocarbon (CFC: component CFC-11) dataset was obtained in the subpolar North Atlantic. To estimate the synopticity of the 1997 data, the recent temporal evolution of the CFC and Labrador Sea Water (LSW) thickness fields are examined. In the western Atlantic north of 50degreesN, the LSW thickness decreased considerably from 1994-97, while the mean CFC concentrations did not change much. South of 50degreesN and in the eastern Atlantic, the CFC concentration increased with little or no change in the LSW thickness. On shorter timescales, local anomalies due to the presence of eddies are observed, but for space scales larger than the eddies the dataset can be treated as being synoptic over the 1997 observation period. The spreading of LSW in the subpolar North Atlantic is described in detail using gridded CFC and LSW thickness fields combined with Profiling Autonomous Lagrangian Circulation Explorer (PALACE) float trajectories. The gridded fields are also used to calculate the CFC-11 inventory in the LSW from 40degrees to 65degreesN, and from 10degrees to 60degreesW. In total, 2300 +/- 250 tons of CFC-11 (equivalent to 16.6 million moles) were brought into the LSW by deep convection. In 1997, 28% of the inventory was still found in the Labrador Sea west of 45degreesW and 31% of the inventory was located in the eastern Atlantic. The CFC inventory in the LSW was used to estimate the lower limits of LSW formation rates. At a constant formation rate, a value of 4.4-5.6 Sv (Sv = 10(6) m(3) s(-1)) is obtained. If the denser modes of LSW are ventilated only in periods with intense convection, the minimum formation rate of LSW in 1988-94 is 8.1-10.8 Sv, and 1.8-2.4 Sv in 1995-97.

2001
Prinn, RG, Huang J, Weiss RF, Cunnold DM, Fraser PJ, Simmonds PG, McCulloch A, Harth C, Salameh P, O'Doherty S, Wang RHJ, Porter L, Miller BR.  2001.  Evidence for substantial variations of atmospheric hydroxyl radicals in the past two decades. Science. 292:1882-1888.   10.1126/science.1058673   AbstractWebsite

The hydroxyl radical (OH) is the dominant oxidizing chemical in the atmosphere. It destroys most air pollutants and many gases involved in ozone depletion and the greenhouse effect. Global measurements of 1,1,1-trichloroethane (CH3CCl3, methyl chloroform) provide an accurate method for determining the global and hemispheric behavior of OH. Measurements show that CH3CCl3 Levels rose steadily from 1978 to reach a maximum in 1992 and then decreased rapidly to levels in 2000 that were Lower than the levels when measurements began in 1978. Analysis of these observations shows that global OH Levels were growing between 1978 and 1988, but the growth rate was decreasing at a rate of 0.23 +/- 0.18% year(-2), so that OH Levels began declining after 1988. Overall, the global average OH trend between 1978 and 2000 was -0.64 +/- 0.60% year(-1). These variations imply important and unexpected gaps in current understanding of the capability of the atmosphere to cleanse itself.

1998
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.

1997
Takahashi, T, Feely RA, Weiss RF, Wanninkhof RH, Chipman DW, Sutherland SC, Takahashi TT.  1997.  Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 difference. Proceedings of the National Academy of Sciences of the United States of America. 94:8292-8299.   10.1073/pnas.94.16.8292   AbstractWebsite

Approximately 250,000 measurements made for the pCO(2) difference between surface water and the marine atmosphere, Delta pCO(2), have been assembled for the global oceans. Observations made in the equatorial Pacific during El Nine events have been excluded from the data set, These observations are mapped on the global 4 degrees x 5 degrees grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Nino year. Monthly global distributions of Delta pCO(2) have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO2 across the sea surface has been computed using Delta pCO(2) distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C.yr(-1) depending on different formulations used for wind speed dependence on the gas transfer coefficient, These estimates;Ire subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of Delta pCO(2) over the global oceans, Temperate and polar oceans of the both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans, The Indian and Southern Oceans take up about 20% each.

1995
Prinn, RG, Weiss RF, Miller BR, Huang J, Alyea FN, Cunnold DM, Fraser PJ, Hartley DE, Simmonds PG.  1995.  Atmospheric trends and lifetime of CH3CCI3 and global OH concentrations . Science. 269:187-192.   10.1126/science.269.5221.187   AbstractWebsite

Determination of the atmospheric concentrations and lifetime of trichloroethane (CH3CCl3) is very important in the context of global change. This halocarbon is involved in depletion of ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH3CCl3 in the total atmosphere is 4.8 +/- 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmosphere's oxidizing capability, shows little change from 1978 to 1994.

Nevison, CD, Weiss RF, Erickson DJ.  1995.  Global oceanic emissions of nitrous oxide. Journal of Geophysical Research-Oceans. 100:15809-15820.   10.1029/95jc00684   AbstractWebsite

The global N2O flux from the ocean to the atmosphere is calculated based on more than 60,000 expedition measurements of the N2O anomaly in surface water. The expedition data are extrapolated globally and coupled to daily air-sea gas transfer coefficients modeled at 2.8 degrees x 2.8 degrees resolution to estimate a global ocean source of about 4 (1.2-6.8) Tg N yr(-1). The wide range of uncertainty in the source estimate arises mainly from uncertainties in the air-sea gas transfer coefficients and in the global extrapolation of the summertime-biased surface N2O data set. The strongest source is predicted from the 40-60 degrees S latitude band. Strong emissions also are predicted from the northern Pacific Ocean, the equatorial upwelling zone, and coastal upwelling zones occurring predominantly in the tropical northern hemisphere. High apparent oxygen utilization (AOU) at 100 m below the mixed layer is found to be correlated positively both to N2O production at depth and to the surface N2O anomaly. On the basis of these correlations, the expedition data are partitioned into two subsets associated with high and low AOU at depth. The zonally averaged monthly means in each subset are extrapolated to produce two latitude-by-month matrices in which monthly surface N2O is expressed as the deviation from the annual mean. Both matrices contain large uncertainties. The low-AOU matrix, which mainly includes surface N2O data from the North Atlantic and the subtropical gyres, suggests many regions with positive summer deviations and negative winter deviations, consistent with a seasonal cycle predominantly driven by seasonal heating and cooling of the surface ocean. The high-AOU subset, which includes the regions most important to the global N2O ocean source, suggests some regions with positive winter deviations and negative summer deviations, consistent with a seasonal cycle predominantly driven by wintertime mixing of surface water with N2O-rich deep water. Coupled seasonal changes in gas transfer coefficients and surface N2O in these important source regions could strongly influence the global ocean source.