Publications

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2015
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.

Lunt, MF, Rigby M, Ganesan AL, Manning AJ, Prinn RG, O'Doherty S, Muhle J, Harth CM, Salameh PK, Arnold T, Weiss RF, Saito T, Yokouchi Y, Krummel PB, Steele LP, Fraser PJ, Li SL, Park S, Reimann S, Vollmer MK, Lunder C, Hermansen O, Schmidbauer N, Maione M, Arduini J, Young D, Simmonds PG.  2015.  Reconciling reported and unreported HFC emissions with atmospheric observations. Proceedings of the National Academy of Sciences of the United States of America. 112:5927-5931.   10.1073/pnas.1420247112   AbstractWebsite

We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO2-equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175-221) Tg-CO2-eq.y(-1) in 2007 to 275 (246-304) Tg-CO2-eq.y(-1) in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries. However, our measurement-based estimates of individual HFC species suggest that emissions, from reporting countries, of the most abundant HFC, HFC-134a, were only 79% (63-95%) of the UNFCCC inventory total, while other HFC emissions were significantly greater than the reported values. These results suggest that there are inaccuracies in the reporting methods for individual HFCs, which appear to cancel when aggregated together.

2014
Xiang, B, Patra PK, Montzka SA, Miller SM, Elkins JW, Moore FL, Atlas EL, Miller BR, Weiss RF, Prinn RG, Wofsy SC.  2014.  Global emissions of refrigerants HCFC-22 and HFC-134a: Unforeseen seasonal contributions. Proceedings of the National Academy of Sciences of the United States of America. 111:17379-17384.   10.1073/pnas.1417372111   AbstractWebsite

HCFC-22 (CHClF2) and HFC-134a (CH2FCF3) are two major gases currently used worldwide in domestic and commercial refrigeration and air conditioning. HCFC-22 contributes to stratospheric ozone depletion, and both species are potent greenhouse gases. In this work, we study in situ observations of HCFC-22 and HFC-134a taken from research aircraft over the Pacific Ocean in a 3-y span [Hlaper-Pole-to-Pole Observations (HIPPO) 2009-2011] and combine these data with long-term ground observations from global surface sites [ National Oceanic and Atmospheric Administration (NOAA) and Advanced Global Atmospheric Gases Experiment (AGAGE) networks]. We find the global annual emissions of HCFC-22 and HFC-134a have increased substantially over the past two decades. Emissions of HFC-134a are consistently higher compared with the United Nations Framework Convention on Climate Change (UNFCCC) inventory since 2000, by 60% more in recent years (2009-2012). Apart from these decadal emission constraints, we also quantify recent seasonal emission patterns showing that summertime emissions of HCFC-22 and HFC-134a are two to three times higher than wintertime emissions. This unforeseen large seasonal variation indicates that unaccounted mechanisms controlling refrigerant gas emissions are missing in the existing inventory estimates. Possible mechanisms enhancing refrigerant losses in summer are (i) higher vapor pressure in the sealed compartment of the system at summer high temperatures and (ii) more frequent use and service of refrigerators and air conditioners in summer months. Our results suggest that engineering (e. g., better temperature/vibration-resistant system sealing and new system design of more compact/efficient components) and regulatory (e. g., reinforcing system service regulations) steps to improve containment of these gases from working devices could effectively reduce their release to the atmosphere.

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.

2010
Stohl, A, Kim J, Li S, O'Doherty S, Muhle J, Salameh PK, Saito T, Vollmer MK, Wan D, Weiss RF, Yao B, Yokouchi Y, Zhou LX.  2010.  Hydrochlorofluorocarbon and hydrofluorocarbon emissions in East Asia determined by inverse modeling. Atmospheric Chemistry and Physics. 10:3545-3560.   10.5194/acp-10-3545-2010   AbstractWebsite

The emissions of three hydrochlorofluorocarbons, HCFC-22 (CHClF(2)), HCFC-141b (CH(3)CCl(2)F) and HCFC-142b (CH(3)CClF(2)) and three hydrofluorocarbons, HFC-23 (CHF(3)), HFC-134a (CH(2)FCF(3)) and HFC-152a (CH(3)CHF(2)) from four East Asian countries and the Taiwan region for the year 2008 are determined by inverse modeling. The inverse modeling is based on in-situ measurements of these halocarbons at the Japanese stations Cape Ochi-ishi and Hateruma, the Chinese station Shangdianzi and the South Korean station Gosan. For every station and every 3 h, 20-day backward calculations were made with the Lagrangian particle dispersion model FLEXPART. The model output, the measurement data, bottom-up emission information and corresponding uncertainties were fed into an inversion algorithm to determine the regional emission fluxes. The model captures the observed variation of halocarbon mixing ratios very well for the two Japanese stations but has difficulties explaining the large observed variability at Shangdianzi, which is partly caused by small-scale transport from Beijing that is not adequately captured by the model. Based on HFC-23 measurements, the inversion algorithm could successfully identify the locations of factories known to produce HCFC-22 and emit HFC-23 as an unintentional byproduct. This lends substantial credibility to the inversion method. We report national emissions for China, North Korea, South Korea and Japan, as well as emissions for the Taiwan region. Halocarbon emissions in China are much larger than the emissions in the other countries together and contribute a substantial fraction to the global emissions. Our estimates of Chinese emissions for the year 2008 are 65.3 +/- 6.6 kt/yr for HCFC-22 (17% of global emissions extrapolated from Montzka et al., 2009), 12.1 +/- 1.6 kt/yr for HCFC-141b (22%), 7.3 +/- 0.7 kt/yr for HCFC-142b (17%), 6.2 +/- 0.7 kt/yr for HFC-23 (> 50%), 12.9 +/- 1.7 kt/yr for HFC-134a (9% of global emissions estimated from Velders et al., 2009) and 3.4 +/- 0.5 kt/yr for HFC-152a (7%).

2009
Stohl, A, Seibert P, Arduini J, Eckhardt S, Fraser P, Greally BR, Lunder C, Maione M, Muhle J, O'Doherty S, Prinn RG, Reimann S, Saito T, Schmidbauer N, Simmonds PG, Vollmer MK, Weiss RF, Yokouchi Y.  2009.  An analytical inversion method for determining regional and global emissions of greenhouse gases: Sensitivity studies and application to halocarbons. Atmospheric Chemistry and Physics. 9:1597-1620.   10.5194/acp-9-1597-2009   AbstractWebsite

A new analytical inversion method has been developed to determine the regional and global emissions of long-lived atmospheric trace gases. It exploits in situ measurement data from three global networks and builds on backward simulations with a Lagrangian particle dispersion model. The emission information is extracted from the observed concentration increases over a baseline that is itself objectively determined by the inversion algorithm. The method was applied to two hydrofluorocarbons (HFC-134a, HFC-152a) and a hydrochlorofluorocarbon (HCFC-22) for the period January 2005 until March 2007. Detailed sensitivity studies with synthetic as well as with real measurement data were done to quantify the influence on the results of the a priori emissions and their uncertainties as well as of the observation and model errors. It was found that the global a posteriori emissions of HFC-134a, HFC-152a and HCFC-22 all increased from 2005 to 2006. Large increases (21%, 16%, 18%, respectively) from 2005 to 2006 were found for China, whereas the emission changes in North America (-9%, 23%, 17%, respectively) and Europe (11%, 11%,-4%, respectively) were mostly smaller and less systematic. For Europe, the a posteriori emissions of HFC-134a and HFC-152a were slightly higher than the a priori emissions reported to the United Nations Framework Convention on Climate Change (UNFCCC). For HCFC-22, the a posteriori emissions for Europe were substantially (by almost a factor 2) higher than the a priori emissions used, which were based on HCFC consumption data reported to the United Nations Environment Programme (UNEP). Combined with the reported strongly decreasing HCFC consumption in Europe, this suggests a substantial time lag between the reported time of the HCFC-22 consumption and the actual time of the HCFC-22 emission. Conversely, in China where HCFC consumption is increasing rapidly according to the UNEP data, the a posteriori emissions are only about 40% of the a priori emissions. This reveals a substantial storage of HCFC-22 and potential for future emissions in China. Deficiencies in the geographical distribution of stations measuring halocarbons in relation to estimating regional emissions are also discussed in the paper. Applications of the inversion algorithm to other greenhouse gases such as methane, nitrous oxide or carbon dioxide are foreseen for the future.

2008
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.