Global and regional emission estimates for HCFC-22

Saikawa, E.,Rigby, M.,Prinn, R. G.,Montzka, S. A.,Miller, B. R.,Kuijpers, L. J. M.,Fraser, P. J. B.,Vollmer, M. K.,Saito, T.,Yokouchi, Y.,Harth, C. M.,Mü,hle, J.,Weiss, R. F.,Salameh, P. K.,Kim, J Copernicus GmbH 2012 Atmospheric chemistry and physics Vol.12 No.21

<P>Abstract. 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. </P>

Reconciling reported and unreported HFC emissions with atmospheric observations

Lunt, Mark F.,Rigby, Matthew,Ganesan, Anita L.,Manning, Alistair J.,Prinn, Ronald G.,O’Doherty, Simon,Mü,hle, Jens,Harth, Christina M.,Salameh, Peter K.,Arnold, Tim,Weiss, Ray F.,Saito, Takuya,Y National Academy of Sciences 2015 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.112 No.19

<P><B>Significance</B></P><P>Hydrofluorocarbons (HFCs) are among the atmosphere’s fastest growing, and most potent, greenhouse gases. Proposals have been made to phase down their use over the coming decades. Such initiatives may largely be informed by existing emissions inventories, which, we show, are the subject of significant uncertainty. In this work, we use atmospheric models and measurements to examine the accuracy of these inventories for five major HFCs. We show that, when aggregated together, reported emissions of these HFCs from developed countries are consistent with the atmospheric measurements, and almost half of global emissions now originate from nonreporting countries. However, the agreement between our results and the inventory breaks down for individual HFC emissions, suggesting inaccuracies in the reporting methods for individual compounds.</P><P>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 CO<SUB>2</SUB>-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-CO<SUB>2</SUB>-eq⋅y<SUP>–1</SUP> in 2007 to 275 (246–304) Tg-CO<SUB>2</SUB>-eq⋅y<SUP>–1</SUP> 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.</P>

Characterization of uncertainties in atmospheric trace gas inversions using hierarchical Bayesian methods

Ganesan, A. L.,Rigby, M.,Zammit-Mangion, A.,Manning, A. J.,Prinn, R. G.,Fraser, P. J.,Harth, C. M.,Kim, K.-R.,Krummel, P. B.,Li, S.,Mü,hle, J.,O&,apos,Doherty, S. J.,Park, S.,Salameh, P. K.,Ste Copernicus GmbH 2014 Atmospheric chemistry and physics Vol.14 No.8

<P>Abstract. We present a hierarchical Bayesian method for atmospheric trace gas inversions. This method is used to estimate emissions of trace gases as well as 'hyper-parameters' that characterize the probability density functions (PDFs) of the a priori emissions and model-measurement covariances. By exploring the space of 'uncertainties in uncertainties', we show that the hierarchical method results in a more complete estimation of emissions and their uncertainties than traditional Bayesian inversions, which rely heavily on expert judgment. We present an analysis that shows the effect of including hyper-parameters, which are themselves informed by the data, and show that this method can serve to reduce the effect of errors in assumptions made about the a priori emissions and model-measurement uncertainties. We then apply this method to the estimation of sulfur hexafluoride (SF6) emissions over 2012 for the regions surrounding four Advanced Global Atmospheric Gases Experiment (AGAGE) stations. We find that improper accounting of model representation uncertainties, in particular, can lead to the derivation of emissions and associated uncertainties that are unrealistic and show that those derived using the hierarchical method are likely to be more representative of the true uncertainties in the system. We demonstrate through this SF6 case study that this method is less sensitive to outliers in the data and to subjective assumptions about a priori emissions and model-measurement uncertainties than traditional methods. </P>

History of atmospheric SF6 from 1973 to 2008

Rigby, M.,Mü,hle, J.,Miller, B. R.,Prinn, R. G.,Krummel, P. B.,Steele, L. P.,Fraser, P. J.,Salameh, P. K.,Harth, C. M.,Weiss, R. F.,Greally, B. R.,O&,apos,Doherty, S.,Simmonds, P. G.,Vollmer, M Copernicus GmbH 2010 Atmospheric Chemistry and Physics Vol.10 No.21

<P>Abstract. We present atmospheric sulfur hexafluoride (SF6) 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 pmolmol−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-σ 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 SF6 emissions reported to the UNFCCC were underestimated between at least 2004 and 2005. </P>

Methane emissions in East Asia for 2000-2011 estimated using an atmospheric Bayesian inversion : METHANE EMISSIONS IN EAST ASIA

Thompson, R. L.,Stohl, A.,Zhou, L. X.,Dlugokencky, E.,Fukuyama, Y.,Tohjima, Y.,Kim, S.-Y.,Lee, H.,Nisbet, E. G.,Fisher, R. E.,Lowry, D.,Weiss, R. F.,Prinn, R. G.,O'Doherty, S.,Young, D.,White, J. W. C American Geophysical Union 2015 Journal of geophysical research. Atmospheres Vol.120 No.9

Toward resolving the budget discrepancy of ozone-depleting carbon tetrachloride (CCl4): an analysis of top-down emissions from China

Park, Sunyoung,Li, Shanlan,Mü,hle, Jens,O&,apos,Doherty, Simon,Weiss, Ray F.,Fang, Xuekun,Reimann, Stefan,Prinn, Ronald G. Copernicus GmbH 2018 Atmospheric chemistry and physics Vol.18 No.16

<P>Abstract. Carbon tetrachloride (CCl4) is a first-generation ozone-depleting substance, and its emissive use and production were globally banned by the Montreal Protocol with a 2010 phase-out; however, production and consumption for non-dispersive use as a chemical feedstock and as a process agent are still allowed. This study uses the high frequency and magnitude of CCl4 pollution events from an 8-year real-time atmospheric measurement record obtained at Gosan station (a regional background monitoring site in East Asia) to present evidence of significant unreported emissions of CCl4. Top-down emissions of CCl4 amounting to 23.6±7.1 Gg yr−1 from 2011 to 2015 are estimated for China, in contrast to the most recently reported, post-2010, Chinese bottom-up emissions of 4.3-5.2 Gg yr−1. The missing emissions (∼19 Gg yr−1) for China contribute to approximately 54 % of global CCl4 emissions. It is also shown that 89 %±6 % of CCl4 enhancements observed at Gosan are related to CCl4 emissions from the production of CH3Cl, CH2Cl2, CHCl3 and C2Cl4 and its usage as a feedstock and process agent in chemical manufacturing industries. Specific sources and processes are identified using statistical methods, and it is considered highly unlikely that CCl4 is emitted by dispersive uses such as old landfills, contaminated soils and solvent usage. It is thus crucial to implement technical improvements and better regulation strategies to reduce evaporative losses of CCl4 occurring at the factory and/or process levels. </P>