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Carbon tetrachloride (CCl4) is an ozone-depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl4 emissions from the eastern part of China did not decline between 2009 and 2016. This finding is in contrast to a recent bottom-up estimate, which predicted a significant decrease in emissions after the introduction of production controls. We find eastern Asian emissions of CCl4 to be 16 (9–24) Gg/year on average between 2009 and 2016, with the primary source regions being in eastern China. The spatial distribution of emissions that we derive suggests that the source distribution of CCl4 in China changed during the 8-year study period, indicating a new source or sources of emissions from China's Shandong province after 2012., NASA (Grants NNX16AC98G, NNX07AE89G, NNX11AF17G)

High-frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE), for the period 2003 to 2012, combined with archive flask measurements dating back to 1977, have been used to capture the rapid growth of HFC-143a (CH[subscript 3]CF[subscript 3]) and HFC- 32 (CH[subscript 2]F[subscript 2]) mole fractions and emissions into the atmosphere. Here we report the first in situ global measurements of these two gases. HFC-143a and HFC-32 are the third and sixth most abundant hydrofluorocarbons (HFCs) respectively and they currently make an appreciable contribution to the HFCs in terms of atmospheric radiative forcing (1.7±0.04 and 0.7±0.02mWm[superscript -2] in 2012 respectively). In 2012 the global average mole fraction of HFC- 143a was 13.4±0.3 ppt (1o) in the lower troposphere and its growth rate was 1.4±0.04 ppt yr[superscript -1]; HFC-32 had a global mean mole fraction of 6.2±0.2 ppt and a growth rate of 1.1±0.04 ppt yr [superscript -1] in 2012. The extensive observations presented in this work have been combined with an atmospheric transport model to simulate global atmospheric abundances and derive global emission estimates. It is estimated that 23±3 Gg yr[superscript -1] of HFC-143a and 21±11 Gg yr[superscript -1] of HFC- 32 were emitted globally in 2012, and the emission rates are estimated to be increasing by 7±5%yr[superscript -1] for HFC-143a and 14±11%yr[superscript -1] for HFC-32.

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 355 mW m[superscript −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 240 mW m[superscript −2] by 2050 or a cumulative emissions saving equivalent to 0.5 to 2.8 years 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., Natural Environment Research Council (Great Britain) (Advanced Research Fellowship NE/I021365/1), United States. National Aeronautics and Space Administration (Upper Atmospheric Research Program Grant NNX11AF17G), United States. National Oceanic and Atmospheric Administration

High-frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and System for Observation of halogenated Greenhouse gases in Europe (SOGE) networks for the period 1998 to 2008, combined with archive flask measurements dating back to 1978, have been used to capture the rapid growth of HFC-125 (CHF[subscript 2]CF[subscript 3]) in the atmosphere. HFC-125 is the fifth most abundant HFC, and it currently makes the third largest contribution of the HFCs to atmospheric radiative forcing. At the beginning of 2008 the global average was 5.6 ppt in the lower troposphere and the growth rate was 16% yr[superscript −1]. The extensive observations have been combined with a range of modeling techniques to derive global emission estimates in a top-down approach. It is estimated that 21 kt were emitted globally in 2007, and the emissions are estimated to have increased 15% yr[superscript −1] since 2000. These estimates agree within approximately 20% with values reported to the United Nations Framework Convention on Climate Change (UNFCCC) provided that estimated emissions from East Asia are included. Observations of regionally polluted air masses at individual AGAGE sites have been used to produce emission estimates for Europe (the EU-15 countries), the United States, and Australia. Comparisons between these top-down estimates and bottom-up estimates based on reports by individual countries to the UNFCCC show a range of approximately four in the differences. This process of independent verification of emissions, and an understanding of the differences, is vital for assessing the effectiveness of international treaties, such as the Kyoto Protocol.

We present a comprehensive estimate of nitrous oxide (N[subscript 2]O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N[subscript 2]O are available from measurements at Cape Grim, Tasmania; Cape Matatula, American Samoa; Ragged Point, Barbados; Mace Head, Ireland; and at Trinidad Head, California using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. The Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected discrete air samples in flasks and in situ measurements from remote sites across the globe and analyzed them for a suite of species including N[subscript 2]O. In addition to these major networks, we include in situ and aircraft measurements from the National Institute of Environmental Studies (NIES) and flask measurements from the Tohoku University and Commonwealth Scientific and Industrial Research Organization (CSIRO) networks. All measurements show increasing atmospheric mole fractions of N[subscript 2]O, with a varying growth rate of 0.1–0.7% per year, resulting in a 7.4% increase in the background atmospheric mole fraction between 1979 and 2011. Using existing emission inventories as well as bottom-up process modeling results, we first create globally gridded a priori N[subscript 2]O emissions over the 37 years since 1975. 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 for five source sectors from 13 regions in the world. This is the first time that all of these measurements from multiple networks have been combined to determine emissions. Our inversion indicates that global and regional N[subscript 2]O emissions have an increasing trend between 1995 and 2008. Despite large uncertainties, a significant increase i, NASA Upper Atmospheric Research Program (Grant NNX11AF17G), NASA Upper Atmospheric Research Program (Grant NNX07AF09G), NASA Upper Atmospheric Research Program (Grant NNX07AE87G), United States. National Oceanic and Atmospheric Administration (Contract RA133R09CN0062)

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 (SF[subscript 6]) 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 SF[subscript 6] 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., United States. National Aeronautics and Space Administration (Grant NNX11AF17G), United States. National Aeronautics and Space Administration (Grant NNX11AF16G), United States. National Aeronautics and Space Administration (Grant NNX11AF15G)

High-frequency atmospheric measurements of methane (CH[subscript 4]), nitrous oxide (N[subscript 2]O) and sulfur hexafluoride (SF[subscript 6]) from Darjeeling, India are presented from December 2011 (CH[subscript 4])/March 2012 (N[subscript 2]O and SF[subscript 6]) through February 2013. These measurements were made on a gas chromatograph equipped with a flame ionization detector and electron capture detector, and were calibrated on the Tohoku University, the Scripps Institution of Oceanography (SIO)-98 and SIO-2005 scales for CH[subscript 4], N[subscript 2]O and SF[subscript 6], respectively. The observations show large variability and frequent pollution events in CH[subscript 4] and N[subscript 2]O mole fractions, suggesting significant sources in the regions sampled by Darjeeling throughout the year. By contrast, SF[subscript 6] mole fractions show little variability and only occasional pollution episodes, likely due to weak sources in the region. Simulations using the Numerical Atmospheric dispersion Modelling Environment (NAME) particle dispersion model suggest that many of the enhancements in the three gases result from the transport of pollutants from the densely populated Indo-Gangetic Plains of India to Darjeeling. The meteorology of the region varies considerably throughout the year from Himalayan flows in the winter to the strong south Asian summer monsoon. The model is consistent in simulating a diurnal cycle in CH[subscript 4] and N[subscript 2]O mole fractions that is present during the winter but absent in the summer and suggests that the signals measured at Darjeeling are dominated by large-scale (~100 km) flows rather than local (<10 km) flows., Massachusetts Institute of Technology. Center for Global Change Science (Director's Fund), Massachusetts Institute of Technology. Joint Program on the Science & Policy of Global Change, Martin Family Society of Fellows for Sustainability, MIT Energy Initiative, MIT International Science and Technology Initiative, United States. National Aeronautics and Space Administration (Grant NNX11AF17G), United States. National Oceanic and Atmospheric Administration (Contract RA133R09CN0062)

Nitrogen trifluoride (NF[subscript 3]) has potential to make a growing contribution to the Earth’s radiative budget; however, our understanding of its atmospheric burden and emission rates has been limited. Based on a revision of our previous calibration and using an expanded set of atmospheric measurements together with an atmospheric model and inverse method, we estimate that the global emissions of NF[subscript 3 ] in 2011 were 1.18 ± 0.21 Gg⋅y[superscript −1], or ∼20 Tg CO[subscript 2]-eq⋅y[superscript−1] (carbon dioxide equivalent emissions based on a 100-y global warming potential of 16,600 for NF[subscript 3]). The 2011 global mean tropospheric dry air mole fraction was 0.86 ± 0.04 parts per trillion, resulting from an average emissions growth rate of 0.09 Gg⋅y[superscript −2] over the prior decade. In terms of CO[subscript 2] equivalents, current NF[subscript 3] emissions represent between 17% and 36% of the emissions of other long-lived fluorinated compounds from electronics manufacture. We also estimate that the emissions benefit of using NF[subscript 3] over hexafluoroethane (C[subscript 2]F[subscript 6]) in electronics manufacture is significant—emissions of between 53 and 220 Tg CO[subscript 2]-eq⋅y[superscript −1] were avoided during 2011. Despite these savings, total NF[subscript 3] emissions, currently ~10% of production, are still significantly larger than expected assuming global implementation of ideal industrial practices. As such, there is a continuing need for improvements in NF[subscript 3] emissions reduction strategies to keep pace with its increasing use and to slow its rising contribution to anthropogenic climate forcing., NASA Upper Atmospheric Research Program

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 CH[subscript 3]CCl[subscript 3], 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 CH[subscript 3]CCl[subscript 3] using a multi-species inverse method. A steady-state lifetime of 45 yr for CFC-11, currently recommended in the most recent World Meteorological Organisation (WMO) Scientific Assessments of Ozone Depletion, lies towards the lower uncertainty bound of our estimates, which are 54[61 over 48] yr (1-sigma uncertainty) when AGAGE data were used and 52[61 over 45] yr when the NOAA network data were used. Our derived lifetime for CFC-113 is significantly higher than the WMO estimates of 85 yr, being 109[121 over 99] (AGAGE) and 109[124 over 97] (NOAA). New estimates of the steady-state lifetimes of CFC-12 and CH[subscript 3]CCl[subscript 3] are consistent with the current WMO recommendations, being 111[132 over 95] and 112[136 over 95] yr (CFC-12, AGAGE and NOAA respectively) and 5.04[5.20 over 4.92] and 5.04[5.23 over 4.87] yr (CH[subscript 3]CCl[subscript 3], AGAGE and NOAA respectively)., NASA Upper Atmospheric Research Program (Advanced Global Atmospheric Gases Experiment (AGAGE) Grant NNX07AE89G), NASA Upper Atmospheric Research Program (Advanced Global Atmospheric Gases Experiment (AGAGE) Grant NNX11AF17G)

Atmospheric observations and trends are presented for the high molecular weight perfluorocarbons (PFCs): decafluorobutane (C[subscript 4]F[subscript 10]), dodecafluoropentane (C[subscript 5]F[subscript 12]), tetradecafluorohexane (C[subscript 6]F[subscript 14]), hexadecafluoroheptane (C[subscript 7]F[subscript 16]) and octadecafluorooctane (C[subscript 8]F[subscript 18]). Their atmospheric histories are based on measurements of 36 Northern Hemisphere and 46 Southern Hemisphere archived air samples collected between 1973 to 2011 using the Advanced Global Atmospheric Gases Experiment (AGAGE) "Medusa" preconcentration gas chromatography-mass spectrometry systems. A new calibration scale was prepared for each PFC, with estimated accuracies of 6.8% for C[subscript 4]F[subscript 10], 7.8% for C[subscript 5]F[subscript 12], 4.0% for C[subscript 6]F[subscript 14], 6.6% for C[subscript 7]F[subscript 16] and 7.9% for C[subscript 8]F[subscript 18]. Based on our observations the 2011 globally averaged dry air mole fractions of these heavy PFCs are: 0.17 parts-per-trillion (ppt, i.e., parts per 10[superscript 12]) for C[subscript 4]F[subscript 10], 0.12 ppt for C[subscript 5]F[subscript 12], 0.27 ppt for C[subscript 6]F[subscript 14], 0.12 ppt for C[subscript 7]F[subscript 16] and 0.09 ppt for C[subscript 8]F[subscript 18]. These atmospheric mole fractions combine to contribute to a global average radiative forcing of 0.35 mW m[superscript −2], which is 6% of the total anthropogenic PFC radiative forcing (Montzka and Reimann, 2011; Oram et al., 2012). The growth rates of the heavy perfluorocarbons were largest in the late 1990s peaking at 6.2 parts per quadrillion (ppq, i.e., parts per 10[superscript 15]) per year (yr) for C[subscript 4]F[subscript 10], at 5.0 ppq yr−1 for C[subscript 5]F[subscript 12] and 16.6 ppq yr[superscript −1] for C[subscript 6]F[subscript 14] and in the early 1990s for C7F16 at 4.7 ppq yr−1 and in the mid 1990s for C8F18 at 4.8 ppq yr−1. The 2011 globall, NASA Upper Atmospheric Research Program (Grant number NNX11AF17G)

We report on ground-based atmospheric measurements and emission estimates of the four anthropogenic hydrofluorocarbons (HFCs) HFC-365mfc (CH[subscript 3]CF[subscript 2]CH[subscript 2]CF[subscript 3], 1,1,1,3,3-pentafluorobutane), HFC-245fa (CHF[subscript 2]CH[subscript 2]CF[subscript 3], 1,1,1,3,3-pentafluoropropane), HFC-227ea (CF[subscript 3]CHFCF[subscript 3], 1,1,1,2,3,3,3-heptafluoropropane), and HFC-236fa (CF[subscript 3]CH[subscript 2]CF[subscript 3], 1,1,1,3,3,3-hexafluoropropane). In situ measurements are from the global monitoring sites of the Advanced Global Atmospheric Gases Experiment (AGAGE), the System for Observations of Halogenated Greenhouse Gases in Europe (SOGE), and Gosan (South Korea). We include the first halocarbon flask sample measurements from the Antarctic research stations King Sejong and Troll. We also present measurements of archived air samples from both hemispheres back to the 1970s. We use a two-dimensional atmospheric transport model to simulate global atmospheric abundances and to estimate global emissions. HFC-365mfc and HFC-245fa first appeared in the atmosphere only ∼1 decade ago; they have grown rapidly to globally averaged dry air mole fractions of 0.53 ppt (in parts per trillion, 10[superscript −12]) and 1.1 ppt, respectively, by the end of 2010. In contrast, HFC-227ea first appeared in the global atmosphere in the 1980s and has since grown to ∼0.58 ppt. We report the first measurements of HFC-236fa in the atmosphere. This long-lived compound was present in the atmosphere at only 0.074 ppt in 2010. All four substances exhibit yearly growth rates of >8% yr[superscript −1] at the end of 2010. We find rapidly increasing emissions for the foam-blowing compounds HFC-365mfc and HFC-245fa starting in ∼2002. After peaking in 2006 (HFC-365mfc: 3.2 kt yr[superscript −1], HFC-245fa: 6.5 kt yr[superscript −1]), emissions began to decline. Our results for these two compounds suggest that recent estimates from long-term projections (to the, United States. National Aeronautics and Space Administration (Grant NAG5‐12669), United States. National Aeronautics and Space Administration (Grant NNX07AE89G)

We present atmospheric sulfur hexafluoride (SF6)[SF subscript 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 pmolmol−1 [pmolmol superscript -1] yr−1 [yr superscript -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 [yr superscript -1] (1-σ [1 - delta] 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 emissi, NASA Upper Atmospheric Research Program (Grant NNX07AE89G), NASA Upper Atmospheric Research Program (Grant NNX07AF09G), NASA Upper Atmospheric Research Program (Grant NNX07AE87G), Great Britain. Dept. for Environment, Food & Rural Affairs, United States. National Oceanic and Atmospheric Administration, Commonwealth Scientific and Industrial Research Organization (Australia), Australia. Bureau of Meteorology, Korea. Meteorological Administration. Research and Development Program (Grant CATER 2009-4109)

Carbon tetrachloride (CCl4) has substantial stratospheric ozone depletion potential and its consumption is controlled under the Montreal Protocol and its amendments. We implement a Kalman filter using atmospheric CCl4 measurements and a 3-dimensional chemical transport model to estimate the interannual regional industrial emissions and seasonal global oceanic uptake of CCl4 for the period of 1996–2004. The Model of Atmospheric Transport and Chemistry (MATCH), driven by offline National Center for Environmental Prediction (NCEP) reanalysis meteorological fields, is used to simulate CCl4 mole fractions and calculate their sensitivities to regional sources and sinks using a finite difference approach. High frequency observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Earth System Research Laboratory (ESRL) of the National Oceanic and Atmospheric Administration (NOAA) and low frequency flask observations are together used to constrain the source and sink magnitudes, estimated as factors that multiply the a priori fluxes. Although industry data imply that the global industrial emissions were substantially declining with large interannual variations, the optimized results show only small interannual variations and a small decreasing trend. The global surface CCl4 mole fractions were declining in this period because the CCl4 oceanic and stratospheric sinks exceeded the industrial emissions. Compared to the a priori values, the inversion results indicate substantial increases in industrial emissions originating from the South Asian/Indian and Southeast Asian regions, and significant decreases in emissions from the European and North American regions., United States. National Aeronautics and Space Administration (Grant NNX07AE89G), United States. National Aeronautics and Space Administration (Grant NAG5-12669), United States. National Aeronautics and Space Administration (Grant NAG5-12099), National Science Foundation (U.S.) (grant ATM-0120468), United States. National Aeronautics and Space Administration (Grant NNX07AF09G), United States. National Aeronautics and Space Administration (Grant NNX07AE87G), Great Britain. Department for Environment, Food and Rural Affairs (grants EPG 1/1/159), Great Britain. Department for Environment, Food and Rural Affairs (grant CPEG 24), Great Britain. Department for Environment, Food and Rural Affairs (grants GA01081), Australia. Bureau of Meteorology, CSIRO Marine and Atmospheric Research

We present atmospheric baseline growth rates from the 1970s to the present for the long-lived, strongly infrared-absorbing perfluorocarbons (PFCs) tetrafluoromethane (CF4), hexafluoroethane (C2F6), and octafluoropropane (C3F8) in both hemispheres, measured with improved accuracies (~1–2%) and precisions (<0.3%, or <0.2 ppt (parts per trillion dry air mole fraction), for CF4; <1.5%, or <0.06 ppt, for C2F6; <4.5%, or <0.02 ppt, for C3F8 within the Advanced Global Atmospheric Gases Experiment (AGAGE). Pre-industrial background values of 34.7±0.2 ppt CF4 and 0.1±0.02 ppt C2F6 were measured in air extracted from Greenland ice and Antarctic firn. Anthropogenic sources are thought to be primary aluminum production (CF4, C2F6, C3F8), semiconductor production (C2F6, CF4, C3F8) and refrigeration use (C3F8). Global emissions calculated with the AGAGE 2-D 12-box model are significantly higher than most previous emission estimates. The sum of CF4 and C2F6 emissions estimated from aluminum production and non-metal production are lower than observed global top-down emissions, with gaps of ~6 Gg/yr CF4 in recent years. The significant discrepancies between previous CF4, C2F6, and C3F8 emission estimates and observed global top-down emissions estimated from AGAGE measurements emphasize the need for more accurate, transparent, and complete emission reporting, and for verification with atmospheric measurements to assess the emission sources of these long-lived and potent greenhouse gases, which alter the radiative budget of the atmosphere, essentially permanently, once emitted., United States. National Aeronautics and Space Administration (Upper Atmospheric Research Program grant NNX07AE89G), United States. National Aeronautics and Space Administration (Upper Atmospheric Research Program grant NNX07AF09G), United States. National Aeronautics and Space Administration (Upper Atmospheric Research Program grant NNX07AE87G), Great Britain. Department for Environment, Food and Rural Affairs, United States. National Oceanic and Atmospheric Administration, Commonwealth Scientific and Industrial Research Organization (Australia), Australia. Bureau of Meteorology

HFC-23 (also known as CHF3 [CHF subscript 3], fluoroform or trifluoromethane) is a potent greenhouse gas (GHG), with a global warming potential (GWP) of 14 800 for a 100-year time horizon. It is an unavoidable by-product of HCFC-22 (CHClF2 [CHCIF subscript 2], chlorodifluoromethane) production. HCFC-22, an ozone depleting substance (ODS), is used extensively in commercial refrigeration and air conditioning, in the extruded polystyrene (XPS) foam industries (dispersive applications) and also as a feedstock in fluoropolymer manufacture (a non-dispersive use). Aside from small markets in specialty uses, HFC-23 has historically been considered a waste gas that was, and often still is, simply vented to the atmosphere. Efforts have been made in the past two decades to reduce HFC-23 emissions, including destruction (incineration) in facilities in developing countries under the United Nations Framework Convention on Climate Change's (UNFCCC) Clean Development Mechanism (CDM), and by process optimization and/or voluntary incineration by most producers in developed countries. We present observations of lower-tropospheric mole fractions of HFC-23 measured by "Medusa" GC/MSD instruments from ambient air sampled in situ at the Advanced Global Atmospheric Gases Experiment (AGAGE) network of five remote sites (2007–2009) and in Cape Grim air archive (CGAA) samples (1978–2009) from Tasmania, Australia. These observations are used with the AGAGE 2-D atmospheric 12-box model and an inverse method to produce model mole fractions and a "top-down" HFC-23 emission history. The model 2009 annual mean global lower-tropospheric background abundance is 22.6 (±0.2) pmol mol−1 [mol superscript -1]. The derived HFC-23 emissions show a "plateau" during 1997–2003, followed by a rapid ~50% increase to a peak of 15.0 (+1.3/−1.2) Gg/yr in 2006. Following this peak, emissions of HFC-23 declined rapidly to 8.6 (+0.9/−1.0) Gg/yr in 2009, the lowest annual emission of the past 15 years. We derive a 1990, NASA Upper Atmospheric Research Program (Grant NNX07AE89G), NASA Upper Atmospheric Research Program (Grant NNX07AF09G), NASA Upper Atmospheric Research Program (Grant NNX07AE87G)

Methyl chloride (CH3Cl) [CH subscript 3 Cl] is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. Large uncertainties in estimates of its source and sink magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of the surface fluxes of CH3Cl [CH subscript 3 Cl]. The Model of Atmospheric Transport and Chemistry (MATCH), driven by NCEP interannually varying meteorological data, is then used to simulate CH3Cl [CH subscript 3 Cl] mole fractions and quantify the time series of sensitivities of the mole fractions at each measurement site to the surface fluxes of various regional and global sources and sinks. We then implement the Kalman filter (with the unit pulse response method) to estimate the surface fluxes on regional/global scales with monthly resolution from January 2000 to December 2004. High frequency observations from the AGAGE, SOGE, NIES, and NOAA/ESRL HATS in situ networks and low frequency observations from the NOAA/ESRL HATS flask network are used to constrain the source and sink magnitudes. The inversion results indicate global total emissions around 4100 ± 470 Gg yr−1 [yr superscript -1] with very large emissions of 2200 ± 390 Gg yr−1 [yr superscript -1] from tropical plants, which turn out to be the largest single source in the CH3Cl [CH subscript 3 Cl] budget. Relative to their a priori annual estimates, the inversion increases global annual fungal and tropical emissions, and reduces the global oceanic source. The inversion implies greater seasonal and interannual oscillations of the natural sources and sink of CH3Cl [CH subscript 3 Cl] compared to the a priori. The inversion also reflects the strong effects of the 2002/2003 globally widespread heat waves and droughts on global emissions from tropical plants, biomass burning and salt marshes, and on the soil sink., United States. National Aeronautics and Space Administration (Grant NNX07AE89G), United States. National Aeronautics and Space Administration (Grant NAG5-12669), United States. National Aeronautics and Space Administration (Grant NNX07AF09G), United States. National Aeronautics and Space Administration (Grant NNX07AE87G), National Science Foundation (U.S.) (Grant ATM-0120468), United States. National Aeronautics and Space Administration (Grant NAG5-12099)