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Reimann, S, Elkins JW, Fraser PJ, Hall BD, Kurylo MJ, Mahieu E, Montzka SA, Prinn RG, Rigby M, Simmonds PG, Weiss RF.  2018.  Observing the atmospheric evolution of ozone-depleting substances. Comptes Rendus Geoscience. 350:384-392.   10.1016/j.crte.2018.08.008   AbstractWebsite

The atmospheric observations of ozone-depleting substances (ODSs) have been essential for following their atmospheric response to the production and use restrictions imposed by the Montreal Protocol and its Amendments and Adjustments. ODSs have been used since the first half of the 20th century in industrial and domestic applications. However, their atmospheric growth went unnoticed until the early 1970s, when they were discovered using gas chromatograph-electron capture detection (GC-ECD) instruments. Similar instrumentation formed the basis of global flask and in situ measurements commenced by NOAA and ALE/GAGE/AGAGE in the late 1970s. The combination of these networks, supported by a number of other laboratories, has been essential for following the tropospheric trends of ODSs. Additionally, ground-based remote sensing measurements within NDACC and aircraft-based observation programs have been crucial for measuring the evolution of the ODS abundances over the entire atmosphere. Maintaining these networks at least at their current state is vital for ensuring the on-going verification of the success of the Montreal Protocol. (C) 2018 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Reimann, S, Manning AJ, Simmonds PG, Cunnold DM, Wang RHJ, Li JL, McCulloch A, Prinn RG, Huang J, Weiss RF, Fraser PJ, O'Doherty S, Greally BR, Stemmler K, Hill M, Folini D.  2005.  Low European methyl chloroform emissions inferred from long-term atmospheric measurements. Nature. 433:506-508.   10.1038/nature03220   AbstractWebsite

Methyl chloroform (CH3CCl3, 1,1,1,-trichloroethane) was used widely as a solvent before it was recognized to be an ozone-depleting substance and its phase-out was introduced under the Montreal Protocol(1). Subsequently, its atmospheric concentration has declined steadily(2-4) and recent European methyl chloroform consumption and emissions were estimated to be less than 0.1 gigagrams per year(1,5). However, data from a short-term tropospheric measurement campaign ( EXPORT) indicated that European methyl chloroform emissions could have been over 20 gigagrams in 2000 (ref. 6), almost doubling previously estimated global emissions(1,4). Such enhanced emissions would significantly affect results from the CH3CCl3 method of deriving global abundances of hydroxyl radicals ( OH) (refs 7 - 12) - the dominant reactive atmospheric chemical for removing trace gases related to air pollution, ozone depletion and the greenhouse effect. Here we use long-term, high-frequency data from MaceHead, Ireland and Jungfraujoch, Switzerland, to infer European methyl chloroform emissions. We find that European emission estimates declined from about 60 gigagrams per year in the mid-1990s to 0.3 - 1.4 and 1.9 - 3.4 gigagrams per year in 2000 - 03, based on Mace Head and Jungfraujoch data, respectively. Our European methyl chloroform emission estimates are therefore higher than calculated from consumption data(1,5), but are considerably lower than those derived from the EXPORT campaign in 2000 ( ref. 6).

Reverdin, G, Weiss RF, Jenkins WJ.  1993.  Ventilation of the Atlantic Ocean equatorial thermocline. Journal of Geophysical Research-Oceans. 98:16289-16310.   10.1029/93jc00976   AbstractWebsite

The ventilation of the lower equatorial Atlantic thermocline (100 m to 400 m) is investigated from the distributions of salinity, oxygen, the chlorofluoromethanes F-11 and F-12, tritium, and the excess helium 3; 1983 data suggest a correlation on isopycnal surfaces between oxygen, chlorofluoromethanes and to a lesser extent, with the apparent ages derived from F-11/F-12 and helium 3/tritium. The apparent ages increase with depth from 10 years on sigma(THETA)=26.5 to over 15 years near 400 m. The tracers are largely undersaturated with respect to the surface concentrations corresponding to the apparent ages. We investigate the ventilation processes responsible for these distributions with simple circulation models, where water from the subtropical gyres reaches isopycnally the equatorial thermocline. The few model parameters are determined by fitting the simulations to the chlorofluoromethane distributions in 1983. The sensitivity of these parameters to expected errors on the past surface concentrations and to vertical mixing is comparable and can result in an error of more than 20% in the model parameters. In 1983, model [H-3] and [He-3]* are too large, in particular when no diapycnal mixing is modeled, but the differences could have arisen from errors on past surface concentrations. During the 1980s, die model overestimates the increase in chlorofluoromethanes, in particular F-12. The fitted model inflow from the southern subtropical gyre between 110 m and 400 m is 14 x 10(6) m3 s-1, in the range of expected transports by the western boundary current near Brazil. The model oxygen utilization rate is on the order of 12 mmol kg-1 yr-1 at 100 m and 5 mmol kg-1 yr-1 at 400 m (below sigma(theta)=27.1).

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   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.

Rhew, RC, Miller BR, Bill M, Goldstein AH, Weiss RF.  2002.  Environmental and biological controls on methyl halide emissions from southern California coastal salt marshes. Biogeochemistry. 60:141-161.   10.1023/a:1019812006560   AbstractWebsite

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) emission rates from southern California coastal salt marshes show large spatial and temporal variabilities that are strongly linked to biological and environmental factors. Here we discuss biogeochemical lines of evidence pointing to vegetation as the primary source of CH3Br and CH3Cl emissions from salt marshes. Sediments and macroalgae do not appear to be major producers of these compounds, based on observations that the highest fluxes are not inhibited by soil inundation; their emissions are not correlated with those of certain gases produced in soils; and emissions from mudflat- and macroalgae-dominated sites are relatively small. In contrast, the seasonal and spatial variabilities of methyl halide fluxes in these salt marshes are consistent with the production of these compounds by vascular plants, although the possibility of production by microflora or fungi associated with the salt marsh vegetation is not ruled out. Flux chamber measurements of emission rates are largely correlated to the overall plant biomass enclosed in the chamber, but appear also to be highly dependent on the predominant plant species. Emission rates follow a diurnal trend similar to the trends of ambient air temperature and photosynthetically active radiation, but not surface soil temperature. Diurnal variabilities in the carbon isotope compositions of CH3Cl and CH3Br and their relative ratios of emissions are consistent with simultaneously competing mechanisms of uptake and production.

Rhew, RC, Miller BR, Weiss RF.  2000.  Natural methyl bromide and methyl chloride emissions from coastal salt marshes. Nature. 403:292-295.   10.1038/35002043   AbstractWebsite

Atmospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl), compounds that are involved in stratospheric ozone depletion, originate from both natural and anthropogenic sources. Current estimates of CH3Br and CH3Cl emissions from oceanic sources, terrestrial plants and fungi, biomass burning and anthropogenic inputs do not balance their losses owing to oxidation by hydroxyl radicals, oceanic degradation, and consumption in soils, suggesting that additional natural terrestrial sources may be important(1). Here we show that CH3Br and CH3Cl are released to the atmosphere from all vegetation zones of two coastal salt marshes. We see very large fluxes of CH3Br and CH3Cl per unit area: up to 42 and 570 mu mol m(-2) d(-1), respectively. The fluxes show large diurnal, seasonal and spatial variabilities, but there is a strong correlation between the fluxes of CH3Br and those of CH3Cl, with an average molar flux ratio of roughly 1:20. If our measurements are typical of salt marshes globally, they suggest that such ecosystems, even though they constitute less than 0.1% of the global surface area(2), may produce roughly 10% of the total fluxes of atmospheric CH3Br and CH3Cl.

Rhew, RC, Miller BR, Vollmer MK, Weiss RF.  2001.  Shrubland fluxes of methyl bromide and methyl chloride. Journal of Geophysical Research-Atmospheres. 106:20875-20882.   10.1029/2001jd000413   AbstractWebsite

Flux measurements in coastal sage scrub, chamise chaparral, and creosote bush scrub environments show that methyl bromide (CH(3)Br) and methyl chloride (CH(3)Cl), compounds that are involved in stratospheric ozone depletion, are both produced and consumed by southern California shrubland ecosystems. CH(3)Br and CH(3)Cl are produced in association with a variety of plants and are consumed by the soils, although there is a large variability in the fluxes, depending on predominant vegetation and environmental conditions. At sites with a net uptake of both compounds the fluxes of CH(3)Cl and CH(3)Br show a strong correlation, with a molar ratio of roughly 40:1, pointing to a similar mechanism of consumption. In contrast, the net production rates of these compounds show no apparent correlation with each other. The average observed net CH(3)Br uptake rates are an order of magnitude smaller than the previously reported average soil consumption rates assigned to shrublands. Extrapolations from our field measurements suggest that shrublands globally have a maximum net consumption of <1 Gg yr(-1) for CH(3)Br and < 20 Gg yr(-1) for CH(3)Cl and may, in fact, be net sources for these compounds. Consequently, the measured net fluxes from shrubland ecosystems can account for part of the present imbalance in the CH(3)Br budget by adding a new source term and potentially reducing the soil sink term. These results also suggest that while shrubland soil consumption of CH(3)Cl may be small, soils in general may be a globally significant sink for CH(3)Cl.

Rhew, RC, Miller BR, Weiss RF.  2008.  Chloroform, carbon tetrachloride and methyl chloroform fluxes in southern California ecosystems. Atmospheric Environment. 42:7135-7140.   10.1016/j.atmosenv.2008.05.038   AbstractWebsite

Chloroform (CHCl3), carbon tetrachloride (CCl4), and methyl chloroform (CH3CCl3) are important carriers of chlorine to the stratosphere and account for an estimated 159 of the total organic chlorine in the troposphere, roughly equivalent to chlorine load due to methyl chloride (CH3Cl). The tropospheric burden of chlorine has declined since 1994, largely due to the restriction of CH3CCl3 and CCl4 use as specified by the Montreal Protocol. However, few field studies have been conducted on the terrestrial-atmosphere exchange of these chlorinated hydrocarbons, leading to uncertainties about the natural cycling of these trace gases. This work shows the results of 75 flux measurements conducted in a variety of southern California ecosystems, including coast sagebrush, chamise chaparral, creosote bush scrub, shoreline, and coastal salt marsh. We find no evidence of a significant soil sink in these ecosystems but rather a small net source of CHCl3 and possibly CCl4. (c) 2008 Elsevier Ltd. All rights reserved.

Rhoderick, GC, Hall BD, Harth CM, Kim JS, Lee J, Montzka SA, Mühle J, Reimann S, Vollmer MK, Weiss RF.  2015.  Comparison of halocarbon measurements in an atmospheric dry whole air sample. Elem Sci Anth..   10.12952/journal.elementa.000075   Abstract

The growing awareness of climate change/global warming, and continuing concerns regarding stratospheric ozone depletion, will require continued measurements and standards for many compounds, in particular halocarbons that are linked to these issues. In order to track atmospheric mole fractions and assess the impact of policy on emission rates, it is necessary to demonstrate measurement equivalence at the highest levels of accuracy for assigned values of standards. Precise measurements of these species aid in determining small changes in their atmospheric abundance. A common source of standards/scales and/or well-documented agreement of different scales used to calibrate the measurement instrumentation are key to understanding many sets of data reported by researchers. This report describes the results of a comparison study among National Metrology Institutes and atmospheric research laboratories for the chlorofluorocarbons (CFCs) dichlorodifluoromethane (CFC-12), trichlorofluoromethane (CFC-11), and 1,1,2-trichlorotrifluoroethane (CFC-113); the hydrochlorofluorocarbons (HCFCs) chlorodifluoromethane (HCFC-22) and 1-chloro-1,1-difluoroethane (HCFC-142b); and the hydrofluorocarbon (HFC) 1,1,1,2-tetrafluoroethane (HFC-134a), all in a dried whole air sample. The objective of this study is to compare calibration standards/scales and the measurement capabilities of the participants for these halocarbons at trace atmospheric levels. The results of this study show agreement among four independent calibration scales to better than 2.5% in almost all cases, with many of the reported agreements being better than 1.0%.

Rhoderick, G, Guenther F, Duewer D, Lee J, Kim JS, Hall B, Weiss R, Harth C, Reimann S, Vollmer M.  2014.  CCQM-P151 final report pilot study CCQM P151 halocarbons in dry whole air. Metrologia. 51 AbstractWebsite

The growing awareness of climate change/global warming and continuing concerns regarding stratospheric ozone depletion will require future measurements and standards for many compounds, in particular halocarbons that are linked to these issues. In order to track and control the emissions of these species globally in the atmosphere, it is necessary to demonstrate measurement equivalence at the highest levels of accuracy for assigned values of standards. This report describes the results of a pilot study between National Metrology Institutes and atmospheric research laboratories for several of the more important halocarbons at atmospheric concentration levels. The comparison includes the chlorofluorocarbons (CFCs) dichlorodifluoromethane (CFC 12), trichlorofluoromethane (CFC 11), and 1,1,2- trichlorotrifluoroethane (CFC 113); the hydrochlorofluorocarbons (HCFCs) chlorodifluoromethane (HCFC 22) and 1-chloro-1,1-difluoroethane (HCFC 142b); and the hydrofluorocarbon (HFC) 1,1,1,2 tetrafluoroethane (HFC 134a), all in a dried whole air sample. The objective of this key comparison is to compare the measurement capabilities of the participants for these halocarbons at trace atmospheric levels.

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.

Rigby, M, Prinn RG, Fraser PJ, Simmonds PG, Langenfelds RL, Huang J, Cunnold DM, Steele LP, Krummel PB, Weiss RF, O'Doherty S, Salameh PK, Wang HJ, Harth CM, Muhle J, Porter LW.  2008.  Renewed growth of atmospheric methane. Geophysical Research Letters. 35   10.1029/2008gl036037   AbstractWebsite

Following almost a decade with little change in global atmospheric methane mole fraction, we present measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) networks that show renewed growth starting near the beginning of 2007. Remarkably, a similar growth rate is found at all monitoring locations from this time until the latest measurements. We use these data, along with an inverse method applied to a simple model of atmospheric chemistry and transport, to investigate the possible drivers of the rise. Specifically, the relative roles of an increase in emission rate or a decrease in concentration of the hydroxyl radical, the largest methane sink, are examined. We conclude that: 1) if the annual mean hydroxyl radical concentration did not change, a substantial increase in emissions was required simultaneously in both hemispheres between 2006 and 2007; 2) if a small drop in the hydroxyl radical concentration occurred, consistent with AGAGE methyl chloroform measurements, the emission increase is more strongly biased to the Northern Hemisphere. Citation: Rigby, M., et al. (2008), Renewed growth of atmospheric methane, Geophys. Res. Lett., 35, L22805, doi: 10.1029/2008GL036037.

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.

Rigby, M, Montzka SA, Prinn RG, White JWC, Young D, O’Doherty S, Lunt MF, Ganesan AL, Manning AJ, Simmonds PG, Salameh PK, Harth CM, Mühle J, Weiss RF, Fraser PJ, Steele PL, Krummel PB, McCulloch A, Park S.  2017.  Role of atmospheric oxidation in recent methane growth. Proceedings of the National Academy of Sciences.   10.1073/pnas.1616426114   Abstract

The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH4 sink, in the recent CH4 growth. We also examine the influence of systematic uncertainties in OH concentrations on CH4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH3CCl3), which is lost primarily through reaction with OH, to estimate OH levels as well as CH3CC3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH4 emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH4 emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13CH4/12CH4 ratio and the recent growth in C2H6. Our approach indicates that significant OH-related uncertainties in the CH4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH4 emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered.

Rigby, M, Prinn RG, O'Doherty S, Montzka SA, McCulloch A, Harth CM, Muhle J, Salameh PK, Weiss RF, Young D, Simmonds PG, Hall BD, Dutton GS, Nance D, Mondeel DJ, Elkins JW, Krummel PB, Steele LP, Fraser PJ.  2013.  Re-evaluation of the lifetimes of the major CFCs and CH3CCl3 using atmospheric trends. Atmospheric Chemistry and Physics. 13:2691-2702.   10.5194/acp-13-2691-2013   AbstractWebsite

Since the Montreal Protocol on Substances that Deplete the Ozone Layer and its amendments came into effect, growth rates of the major ozone depleting substances (ODS), particularly CFC-11, -12 and -113 and CH3CCl3, have declined markedly, paving the way for global stratospheric ozone recovery. Emissions have now fallen to relatively low levels, therefore the rate at which this recovery occurs will depend largely on the atmospheric lifetime of these compounds. The first ODS measurements began in the early 1970s along with the first lifetime estimates calculated by considering their atmospheric trends. We now have global mole fraction records spanning multiple decades, prompting this lifetime re-evaluation. Using surface measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the National Oceanic and Atmospheric Administration Global Monitoring Division (NOAA GMD) from 1978 to 2011, we estimated the lifetime of CFC-11, CFC-12, CFC-113 and CH3CCl3 usin!