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Greally, BR, Simmonds PG, O'Doherty S, McCulloch A, Miller BR, Salameh PK, Muhle J, Tanhua T, Harth C, Weiss RF, Fraser PJ, Krummel PB, Dunse BL, Porter LW, Prinn RG.  2005.  Improved continuous in situ measurements of C1–C3 PFCs, HFCs, HCFCs, CFCs and SF6 in Europe and Australia. Environmental Sciences. 2:253-261.   10.1080/15693430500402614   Abstract

Improved monitoring of non-CO2 greenhouse gases in air samples is presented, achieved using a new analytical system based on preconcentration, gas-chromatography and mass spectrometry. In addition to the major HFCs, HCFCs and CFCs, the new observations include the first in situ time series of the C1–C3 PFCs (CF4, C2F6 and C3F8) and the more volatile of the HFCs (CHF3, CH2F2, CH3CF3) alongside SF6, all of which are now monitored routinely as part of the Advanced Global Atmospheric Gases Experiment (AGAGE). Observed trends in newly monitored species are shown, obtained from 1–2 years continuous in situ air analyses at remote monitoring sites at Mace Head (Ireland) and Cape Grim (Australia). Observed deviations in the air background for these gas species are linked to modelled trajectories of air masses arriving at the monitoring stations to indicate potential source regions for emissions in Europe and Australia. In addition, preliminary estimates of 2004 mixing ratio growth rates of compounds are deduced from the observations, which highlight the importance of continuous atmospheric monitoring for verification of consumption-based emission estimates of non-CO2 greenhouse gases.

O'Doherty, S, Simmonds PG, Cunnold DM, Wang HJ, Sturrock GA, Fraser PJ, Ryall D, Derwent RG, Weiss RF, Salameh P, Miller BR, Prinn RG.  2001.  In situ chloroform measurements at Advanced Global Atmospheric Gases Experiment atmospheric research stations from 1994 to 1998. Journal of Geophysical Research-Atmospheres. 106:20429-20444.   10.1029/2000jd900792   AbstractWebsite

Measurements of atmospheric chloroform (CHCl3) by in situ gas chromatography using electron capture detection are reported from the Advanced Global Atmospheric Gases Experiment (AGAGE) network of atmospheric research stations. They are some of the most comprehensive in situ, high-frequency measurements to be reported for CHCl3 and provide valuable information not only on clean "baseline" mixing ratios but also on local and regional sources. Emissions from these sources cause substantial periodic increases in CHCl3 concentrations above their baseline levels, which can be used to identify source strengths. This is particularly the case for measurements made at Mace Head, Ireland. Furthermore, these local sources of CHCl3 emissions are significant in relation to current estimates of global emissions and illustrate that the understanding of competing sources and sinks of CHCl3 is still fragmentary. These observations also show that CHCl3 has a very pronounced seasonal cycle with a summer minimum and winter maximum presumably resulting from enhanced destruction by OH in the summer. The amplitude of the cycle is dependent on sampling location. Over the 57 months of in situ measurements a global average baseline concentration of 8.9 +/-0.1 ppt was determined with no appreciable trend in the baseline detected.

Cunnold, DM, Steele LP, Fraser PJ, Simmonds PG, Prinn RG, Weiss RF, Porter LW, O'Doherty S, Langenfelds RL, Krummel PB, Wang HJ, Emmons L, Tie XX, Dlugokencky EJ.  2002.  In situ measurements of atmospheric methane at GAGE/AGAGE sites during 1985-2000 and resulting source inferences. Journal of Geophysical Research-Atmospheres. 107   10.1029/2001jd001226   AbstractWebsite

[1] Continuous measurements of methane since 1986 at the Global Atmospherics Gases Experiment/Advanced Global Atmospherics Gases Experiment (GAGE/AGAGE) surface sites are described. The precisions range from approximately 10 ppb at Mace Head, Ireland, during GAGE to better than 2 ppb at Cape Grim, Tasmania, during AGAGE (i.e., since 1993). The measurements exhibit good agreement with coincident measurements of air samples from the same locations analyzed by Climate Monitoring and Diagnostics Laboratory (CMDL) except for differences of approximately 5 ppb before 1989 (GAGE lower) and about 4 ppb from 1991 to 1995 (GAGE higher). These results are obtained before applying a factor of 1.0119 to the GAGE/AGAGE values to place them on the Tohoku University scale. The measurements combined with a 12-box atmospheric model and an assumed atmospheric lifetime of 9.1 years indicates net annual emissions (emissions minus soil sinks) of 545 Tg CH4 with a variability of only +/-20 Tg from 1985 to 1997 but an increase in the emissions in 1998 of 37 +/- 10 Tg. The effect of OH changes inferred by Prinn et al. [2001] is to increase the estimated methane emissions by approximately 20 Tg in the mid-1980s and to reduce them by 20 Tg in 1997 and by more thereafter. Using a two-dimensional (2-D), 12-box model with transport constrained by the GAGE/AGAGE chlorofluorocarbon measurements, we calculate that the proportion of the emissions coming from the Northern Hemisphere is between 73 and 81%, depending on the OH distribution used. However, this result includes an adjustment of 5% derived from a simulation of the 2-D estimation procedure using the 3-D MOZART model. This adjustment is needed because of the very different spatial emission distributions of the chlorofluorocarbons and methane which makes chlorofluorocarbons derived transport rates inaccurate for the 2-D simulation of methane. The 2-D model combined with the annual cycle in OH from Spivakovsky et al. [2000] provide an acceptable fit to the observed 12-month cycles in methane. The trend in the amplitude of the annual cycle of methane at Cape Grim is used to infer a trend in OH in 30degrees-90degreesS of 0 +/- 5% per decade from 1985 to 2000, in qualitative agreement with Prinn et al. [2001] for the Southern Hemisphere.

Fortems-Cheiney, A, Saunois M, Pison I, Chevallier F, Bousquet P, Cressot C, Montzka SA, Fraser PJ, Vollmer MK, Simmonds PG, Young D, O'Doherty S, Weiss RF, Artuso F, Barletta B, Blake DR, Li S, Lunder C, Miller BR, Park S, Prinn R, Saito T, Steele LP, Yokouchi Y.  2015.  Increase in HFC-134a emissions in response to the success of the Montreal Protocol. Journal of Geophysical Research-Atmospheres. 120   10.1002/2015jd023741   AbstractWebsite

The 1,1,1,2-tetrafluoroethane (HFC-134a), an important alternative to CFC-12 in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer, is a high global warming potential greenhouse gas. Here we evaluate variations in global and regional HFC-134a emissions and emission trends, from 1995 to 2010, at a relatively high spatial and temporal (3.75 degrees in longitude x 2.5 degrees in latitude and 8 day) resolution, using surface HFC-134a measurements. Our results show a progressive increase of global HFC-134a emissions from 19 +/- 2 Gg/yr in 1995 to 167 +/- 5 Gg/yr in 2010, with both a slowdown in developed countries and a 20%/yr increase in China since 2005. A seasonal cycle is also seen since 2002, which becomes enhanced over time, with larger values during the boreal summer.

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.

Simmonds, PG, Manning AJ, Athanassiadou M, Scaife AA, Derwent RG, O'Doherty S, Harth CM, Weiss RF, Dutton GS, Hall BD, Sweeney C, Elkins JW.  2013.  Interannual fluctuations in the seasonal cycle of nitrous oxide and chlorofluorocarbons due to the Brewer-Dobson circulation. Journal of Geophysical Research-Atmospheres. 118:10694-10706.   10.1002/jgrd.50832   AbstractWebsite

The tropospheric seasonal cycles of N2O, CFC-11 (CCl3F), and CFC-12 (CCl2F2) are influenced by atmospheric dynamics. The interannually varying summertime minima in mole fractions of these trace gases have been attributed to interannual variations in mixing of stratospheric air (depleted in CFCs and N2O) with tropospheric air with a few months lag. The amount of wave activity that drives the stratospheric circulation and influences the winter stratospheric jet and subsequent mass transport across the tropopause appears to be the primary cause of this interannual variability. We relate the observed seasonal minima of species at three Northern Hemisphere sites (Mace Head, Ireland; Trinidad Head, U.S.; and Barrow, Alaska) with the behavior of the winter stratospheric jet. As a result, a good correlation is obtained between zonal winds in winter at 10 hPa, 58°N–68°N, and the detrended seasonal minima in the stratosphere-influenced tracers. For these three tracers, individual Pearson correlation coefficients (r) between 0.51 and 0.71 were found, with overall correlations of between 0.67 and 0.77 when “composite species” were considered. Finally, we note that the long-term observations of CFCs and N2O in the troposphere provide an independent monitoring method complementary to satellite data. Furthermore, they could provide a useful observational measure of the strength of stratosphere-troposphere exchange and, thus, could be used to monitor any long-term trend in the Brewer-Dobson circulation which is predicted by climate models to increase over the coming decades.

Thompson, RL, Dlugokencky E, Chevallier F, Ciais P, Dutton G, Elkins JW, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, O'Doherty S, Krummel PB, Fraser P, Steele LP.  2013.  Interannual variability in tropospheric nitrous oxide. Geophysical Research Letters. 40:4426-4431.   10.1002/grl.50721   AbstractWebsite

Observations of tropospheric N2O mixing ratio show significant variability on interannual timescales (0.2ppb, 1 standard deviation). We found that interannual variability in N2O is weakly correlated with that in CFC-12 and SF6 for the northern extratropics and more strongly correlated for the southern extratropics, suggesting that interannual variability in all these species is influenced by large-scale atmospheric circulation changes and, for SF6 in particular, interhemispheric transport. N2O interannual variability was not, however, correlated with polar lower stratospheric temperature, which is used as a proxy for stratosphere-to-troposphere transport in the extratropics. This suggests that stratosphere-to-troposphere transport is not a dominant factor in year-to-year variations in N2O growth rate. Instead, we found strong correlations of N2O interannual variability with the Multivariate ENSO Index. The climate variables, precipitation, soil moisture, and temperature were also found to be significantly correlated with N2O interannual variability, suggesting that climate-driven changes in soil N2O flux may be important for variations in N2O growth rate.

Arnold, T, Manning AJ, Kim J, Li SL, Webster H, Thomson D, Muhle J, Weiss RF, Park S, O'Doherty S.  2018.  Inverse modelling of CF4 and NF3 emissions in East Asia. Atmospheric Chemistry and Physics. 18:13305-13320.   10.5194/acp-18-13305-2018   AbstractWebsite

Decadal trends in the atmospheric abundances of carbon tetrafluoride (CF4) and nitrogen trifluoride (NF3) have been well characterised and have provided a time series of global total emissions. Information on locations of emissions contributing to the global total, however, is currently poor. We use a unique set of measurements between 2008 and 2015 from the Gosan station, Jeju Island, South Korea (part of the Advanced Global Atmospheric Gases Experiment network), together with an atmospheric transport model, to make spatially disaggregated emission estimates of these gases in East Asia. Due to the poor availability of good prior information for this study, our emission estimates are largely influenced by the atmospheric measurements. Notably, we are able to highlight emission hotspots of NF3 and CF4 in South Korea due to the measurement location. We calculate emissions of CF4 to be quite constant between the years 2008 and 2015 for both China and South Korea, with 2015 emissions calculated at 4.3 +/- 2.7 and 0.36 +/- 0.11 Gg yr(-1), respectively. Emission estimates of NF3 from South Korea could be made with relatively small uncertainty at 0.6 +/- 0.07 Gg yr(-1) in 2015, which equates to similar to 1.6% of the country's CO2 emissions. We also apply our method to calculate emissions of CHF3 (HFC-23) between 2008 and 2012, for which our results find good agreement with other studies and which helps support our choice in methodology for CF4 and NF3.

Broecker, WS, Ledwell JR, Takahashi T, Weiss R, Merlivat L, Memery L, Peng TH, Jahne B, Munnich KO.  1986.  Isotopic versus micrometeorologic ocean CO2 fluxes: A serious conflict. Journal of Geophysical Research-Oceans. 91:517-527.   10.1029/JC091iC09p10517   AbstractWebsite

Eddy correlation measurements over the ocean give CO2 fluxes an order of magnitude or more larger than expected from mass balance measurements using radiocarbon and radon 222. In particular, Smith and Jones (1985) reported large upward and downward fluxes in a surf zone at supersaturations of 15% and attributed them to the equilibration of bubbles at elevated pressures. They argue that even on the open ocean such bubble injection may create steady state CO2 supersaturations and that inferences of fluxes based on air-sea pCO2 differences and radon exchange velocities must be made with caution. We defend the global average CO2 exchange rate determined by three independent radioisotopic means: prebomb radiocarbon inventories; global surveys of mixed layer radon deficits; and oceanic uptake of bomb-produced radiocarbon. We argue that laboratory and lake data do not lead one to expect fluxes as large as reported from the eddy correlation technique; that the radon method of determining exchange velocities is indeed useful for estimating CO2 fluxes; that supersaturations of CO2 due to bubble injection on the open ocean are negligible; that the hypothesis that Smith and Jones advance cannot account for the fluxes that they report; and that the pCO2 values reported by Smith and Jones are likely to be systematically much too high. The CO2 fluxes for the ocean measured to date by the micrometeorological method can be reconciled with neither the observed concentrations of radioisotopes of radon and carbon in the oceans nor the tracer experiments carried out in lakes and in wind/wave tunnels.