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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.

Thompson, RL, Chevallier F, Crotwell AM, Dutton G, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, Nakazawa T, Krummel PB, Steele LP, Fraser P, O'Doherty S, Ishijima K, Aoki S.  2014.  Nitrous oxide emissions 1999 to 2009 from a global atmospheric inversion. Atmospheric Chemistry and Physics. 14:1801-1817.   10.5194/acp-14-1801-2014   AbstractWebsite

N2O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 degrees longitude x 2.5 degrees latitude) and at monthly time resolution. Over the 11-year period, the global total N2O source varied from 17.5 to 20.1 Tg a(-1) N. Tropical and subtropical land regions were found to consistently have the highest N2O emissions, in particular in South Asia (20 +/- 3% of global total), South America (13 +/- 4 %) and Africa (19 +/- 3 %), while emissions from temperate regions were smaller: Europe (6 +/- 1 %) and North America (7 +/- 2 %). A significant multi-annual trend in N2O emissions (0.045 Tg a(-2) N) from South Asia was found and confirms inventory estimates of this trend. Considerable interannual variability in the global N2O source was observed (0.8 Tg a(-1) N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a(-1) N, 1 SD) and Africa (0.3 Tg a(-1) N, 1 SD). Notable variability was also found for N2O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a(-1) N, 1 SD, respectively). Interannual variability in the N2O source shows some correlation with the El Nino-Southern Oscillation (ENSO), where El Nino conditions are associated with lower N2O fluxes from soils and from the ocean and vice versa for La Nina conditions.

Kim, J, Li S, Muhle J, Stohl A, Kim SK, Park S, Park MK, Weiss RF, Kim KR.  2012.  Overview of the findings from measurements of halogenated compounds at Gosan (Jeju Island, Korea) quantifying emissions in East Asia. Journal of Integrative Environmental Sciences. 9:71-80.   10.1080/1943815x.2012.696548   AbstractWebsite

With increased economic growth in East Asia, regional emissions of many anthropogenic halogenated compounds now constitute a substantial fraction of the global totals. Here, we summarize recently reported findings from measurements of a wide range of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and other halogenated compounds at Gosan (Jeju Island, Korea) within the advanced global atmospheric gases experiment (AGAGE). General wind patterns at Gosan bring air masses from the surrounding areas, allowing the monitoring of both clean baseline and polluted air masses. We have analyzed our measurements since November 2007 both with an interspecies correlation method and with an inversion method based on the FLEXPART Lagrangian particle dispersion model to estimate these regional emissions. The results show that emissions of halogenated compounds in East Asia account for over 20% of global emissions, both in terms of ozone depletion potential (ODP) and global warming potential (GWP), and emphasize the importance of atmospheric measurements for quantifying emissions of these compounds in this region.

Saikawa, E, Rigby M, Prinn RG, Montzka SA, Miller BR, Kuijpers LJM, Fraser PJB, Vollmer MK, Saito T, Yokouchi Y, Harth CM, Muhle J, Weiss RF, Salameh PK, Kim J, Li S, Park S, Kim KR, Young D, O'Doherty S, Simmonds PG, McCulloch A, Krummel PB, Steele LP, Lunder C, Hermansen O, Maione M, Arduini J, Yao B, Zhou LX, Wang HJ, Elkins JW, Hall B.  2012.  Global and regional emission estimates for HCFC-22. Atmospheric Chemistry and Physics. 12:10033-10050.   10.5194/acp-12-10033-2012   AbstractWebsite

HCFC-22 (CHClF2, chlorodifluoromethane) is an ozone-depleting substance (ODS) as well as a significant greenhouse gas (GHG). HCFC-22 has been used widely as a refrigerant fluid in cooling and air-conditioning equipment since the 1960s, and it has also served as a traditional substitute for some chlorofluorocarbons (CFCs) controlled under the Montreal Protocol. A low frequency record on tropospheric HCFC-22 since the late 1970s is available from measurements of the Southern Hemisphere Cape Grim Air Archive (CGAA) and a few Northern Hemisphere air samples (mostly from Trinidad Head) using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. Since the 1990s high-frequency, high-precision, in situ HCFC-22 measurements have been collected at these AGAGE stations. Since 1992, the Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected flasks on a weekly basis from remote sites across the globe and analyzed them for a suite of halocarbons including HCFC-22. Additionally, since 2006 flasks have been collected approximately daily at a number of tower sites across the US and analyzed for halocarbons and other gases at NOAA. All results show an increase in the atmospheric mole fractions of HCFC-22, and recent data show a growth rate of approximately 4% per year, resulting in an increase in the background atmospheric mole fraction by a factor of 1.7 from 1995 to 2009. Using data on HCFC-22 consumption submitted to the United Nations Environment Programme (UNEP), as well as existing bottom-up emission estimates, we first create globally-gridded a priori HCFC-22 emissions over the 15 yr since 1995. We then use the three-dimensional chemical transport model, Model for Ozone and Related Chemical Tracers version 4 (MOZART v4), and a Bayesian inverse method to estimate global as well as regional annual emissions. Our inversion indicates that the global HCFC-22 emissions have an increasing trend between 1995 and 2009. We further find a surge in HCFC-22 emissions between 2005 and 2009 from developing countries in Asia - the largest emitting region including China and India. Globally, substantial emissions continue despite production and consumption being phased out in developed countries currently.

Li, S, Kim J, Kim KR, Muhle J, Kim SK, Park MK, Stohl A, Kang DJ, Arnold T, Harth CM, Salameh PK, Weiss RF.  2011.  Emissions of halogenated compounds in East Asia determined from measurements at Jeju Island, Korea. Environmental Science & Technology. 45:5668-5675.   10.1021/es104124k   AbstractWebsite

High-frequency in situ measurements at Gosan (Jeju Island, Korea) during November 2007 to December 2008 have been combined with interspecies correlation analysis to estimate national emissions of halogenated compounds (HCs) in East Asia, including the chlorofluorocarbons (CFCs), halons, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF(6)), and other chlorinated and brominated compounds. Our results suggest that overall China is the dominant emitter of HCs in East Asia, however significant emissions are also found in South Korea, Japan and Taiwan for HFC-134a, HFC-143a, C(2)F(6), SF(6), CH(3)CCl(3), and HFC-365mfc. The combined emissions of CFCs, halon-1211, HCFCs, HFCs, PFCs, and SF(6) from all four countries in 2008 are 25.3, 1.6, 135, 42.6, 3.6, and 2.0 kt/a, respectively. They account for approximately 15%, 26%, 29%, 16%, 32%, and 26.5% of global emissions, respectively. Our results show signs that Japan has successfully phased out CFCs and HCFCs in compliance with the Montreal Protocol (MP), Korea has started transitioning from HCFCs to HFCs, while China still significantly consumes HCFCs. Taiwan, while not directly regulated under the MP, is shown to have adapted the use of HFCs. Combined analysis of emission rates and the interspecies correlation matrix presented in this study proves to be a powerful tool for monitoring and diagnosing changes in consumption of HCs in East Asia.

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.

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).

Prinn, RG, Huang J, Weiss RF, Cunnold DM, Fraser PJ, Simmonds PG, McCulloch A, Harth C, Reimann S, Salameh P, O'Doherty S, Wang RHJ, Porter LW, Miller BR, Krummel PB.  2005.  Evidence for variability of atmospheric hydroxyl radicals over the past quarter century. Geophysical Research Letters. 32   10.1029/2004gl022228   AbstractWebsite

The hydroxyl free radical (OH) is the major oxidizing chemical in the atmosphere, destroying about 3.7 petagrams (Pg) of trace gases each year, including many gases involved in ozone depletion, the greenhouse effect and urban air pollution. Measurements of 1,1,1-trichloroethane (methyl chloroform, CH3CCl3), which reacts with OH, provide the most accurate method currently utilized for determining the global behavior of OH. We report that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and have since decreased rapidly to levels in 2004 about 30% of the levels when measurements began in 1978. Analysis of these observations shows that global average OH levels had a small maximum around 1989 and a larger minimum around 1998, with OH concentrations in 2003 being comparable to those in 1979. This post-1998 recovery of OH reported here contrasts with the situation 4 years ago when reported OH was decreasing. The 1997-1999 OH minimum coincides with, and is likely caused by, major global wildfires and an intense El Nino event at this time.