SF6 Emissions Research Articles

Conceptual design of a new SF6 abatement technology using a multi‐bed series reactor for the production of valuable chemicals free of toxic wastes

AbstractConceptual design using multi‐bed series reactors consisting of catalysts and adsorbent beds was performed for a new SF6 abatement and utilization technology free of toxic chemicals to reduce SF6 emissions and produce valuable products like CaF2 and CaSO4 simultaneously. With process simulation studies using Aspen HYSYS®, comparative studies for a single‐bed reactor (SR‐1), a two‐bed series reactor (SR‐2), and a three‐bed series reactor (SR‐3) revealed that more CaF2 and CaSO4 were produced in multi‐bed series reactors compared to a SR‐1 (SR‐3 > SR‐2 > SR‐1) possibly due to sorption‐enhanced hydrolysis. In addition, lower operating temperatures were observed in multi‐bed series reactors (TSR1 > TSR2 > TSR3) showing the positive effect of using multi‐bed series reactors for a simultaneous SF6 abatement and utilization technology.

Assessment of Eco-friendly Gases for Electrical Insulation to Replace the Most Potent Industrial Greenhouse Gas SF6.

Gases for electrical insulation are essential for the operation of electric power equipment. This Review gives a brief history of gaseous insulation that involved the emergence of the most potent industrial greenhouse gas known today, namely sulfur hexafluoride. SF6 paved the way to space-saving equipment for the transmission and distribution of electrical energy. Its ever-rising usage in the electrical grid also played a decisive role in the continuous increase of atmospheric SF6 abundance over the last decades. This Review broadly covers the environmental concerns related to SF6 emissions and assesses the latest generation of eco-friendly replacement gases. They offer great potential for reducing greenhouse gas emissions from electrical equipment but at the same time involve technical trade-offs. The rumors of one or the other being superior seem premature, in particular because of the lack of dielectric, environmental, and chemical information for these relatively novel compounds and their dissociation products during operation.

Assessment of Eco-friendly Gases for Electrical Insulation to Replace the Most Potent Industrial Greenhouse Gas SF6

Gases for electrical insulation are essential for the operation of electric power equipment. This Review gives a brief history of gaseous insulation that involved the emergence of the most potent industrial greenhouse gas known today, namely sulfur hexafluoride. SF6 paved the way to space-saving equipment for the transmission and distribution of electrical energy. Its ever-rising usage in the electrical grid also played a decisive role in the continuous increase of atmospheric SF6 abundance over the last decades. This Review broadly covers the environmental concerns related to SF6 emissions and assesses the latest generation of eco-friendly replacement gases. They offer great potential for reducing greenhouse gas emissions from electrical equipment but at the same time involve technical trade-offs. The rumors of one or the other being superior seem premature, in particular because of the lack of dielectric, environmental, and chemical information for these relatively novel compounds and their dissociation...

CDM implementation towards reduction of fugitive greenhouse gas emissions

Clean Development Mechanism (CDM) is the market-based mechanism introduced to reduce greenhouse gas emissions (GHGs) during various activities. Enormous literature has been available on the GHG mitigation activities in energy, transport, agriculture, construction, waste handling activities, afforestation and reforestation sectors using CDM. However, no single study has been carried out for reduction of fugitive emissions or leakages which releases during the industrial activities. Therefore, this paper presents a critical assessment of CDM projects implemented to reduce fugitive emissions during industrial activities. Out of entire 7749 registered CDM projects (in all sectors of CDM), only 154 (1.98%) fugitive emission reduction projects were implemented up to 2016. These 154 projects contribute up to 147,563,247 MTCO2e (8.87%) estimated emission reduction out of total 1,663,533,108 MTCO2e estimated emission reduction in all sectors of CDM ( https://cdm.unfccc.int/about/index.html ). Out of these 154 registered fugitive projects, 125 projects were assessed for fuel emissions, 19 for halocarbons (HCF) emissions and 10 for sulphur hexafluoride (SF6) emissions. The details of the projects were gathered from Project Design Document (PDDs) of United Nations Framework Convention on Climate Change (UNFCCC) project cycle search and further verified by monitoring the reports of each project. These projects were studied to examine estimated emission reductions with special emphasis on the achieved emission reductions in terms of Certified Emissions Reduction (CERs) to calculate financial benefits. Available CDM methodologies to reduce fugitive emissions were also studied. Further, the distribution of these projects across India was mapped using Arc-GIS. Findings show India is second most country after China in registration of CDM projects. Westerns and northern part of India covers maximum CDM activities. Amongst various methodologies, abatement of methane from coalmines (ACM0008), approved methods decomposition of fluoroform (HFC-23) and point of use abatement device to reduce SF6 emissions (AM0078) were used extensively for reduction of fuel, HFC and fluoride gas emissions. 260,064,195 MTCO2e of CERs (14.5%), i.e. emission reduction was achieved from these projects till 2016 ( https://cdm.unfccc.int/about/index.html ). Therefore, some key challenges or barriers are discussed for development and disclosure of carbon strategies to get transparency in entire CER trading processes.

Background characteristics of atmospheric sulfur hexafluoride concentrations at Zhongshan Station, Antarctica

Sulfur hexafluoride (SF6) is one kind of highly stable anthropogenic greenhouse gas with a global warming potential (GWP) of 2.35×104 over a 100-year time horizon. SF6 emissions are targeted for reduction under the Kyoto Protocol. Therefore it is important for the research about global change to observe atmospheric SF6 background concentrations. Here, we present the patterns for the seasonal and annual variations of atmospheric SF6 concentrations at Zhongshan Station, east Antarctica from February 2008 to January 2013. The prevailing wind direction at the observation site was from the east with the frequency of 92.0%. The average SF6 concentration was about 6.89 pptv under east wind, lower than that under west wind (7.16 pptv). More frequent west wind occurred in autumn and thus average SF6 concentration was higher in autumn than other seasons, indicating that the airflow from western sea area contained higher SF6 concentration than the airflow from east Antarctic continent. On the whole, SF6 concentrations showed an insignificant change under different wind speeds and directions, indicating that the influence of wind and local pollution could be ignored. Our results could represent the background concentrations for atmospheric SF6 at Zhongshan Station. The SF6 concentrations ranged from 6.01 to 7.80 pptv with the average of 6.90±0.40 pptv from February 2008 to January 2013. Annual SF6 concentrations in the atmosphere steadily increased at the rate of 0.28 pptv a - 1, and the increasing magnitudes were very close to each other per year during the period of 2008–2012, similar to the results from other global observation sites, indicating that annual SF6 emission amount could be almost stable each year. No evident periodical changes in SF6 concentrations were observed during the five years. The seasonal SF6 concentration did not show insignificant variation in spring and summer, but an evident decrease in its level occurred in autumn, and then it rose back to normal level in winter. Combined our data with those from other nine observation sites, atmospheric SF6 concentrations showed an evident gradient change with the latitudes at the global scale, and its concentrations in the Northern Hemisphere were 0.3–0.4 pptv higher than those in the Southern Hemisphere because the main emission sources for atmospheric SF6 concentrated in the Northern Hemisphere. The primary source for atmospheric SF6 is industrial emissions in the Northern Hemisphere, whereas its main source is the SF6 southward transportation in the Southern Hemisphere. Our results prove that atmospheric SF6 concentration is continuously growing and its industrial emission control needs to be strengthened. Antarctica is less affected by human activities on the globe, which makes it an ideal area to observe SF6 background concentrations. Our data in the present study will guide industry in optimizing and controlling the SF6 emissions. The SF6 sources and its transportation pathways will be further studied at Zhongshan Station in the future.

US consumption and supplies of sulphur hexafluoride reported under the greenhouse gas reporting program

Under the Greenhouse Gas Reporting Program (GHGRP), the US Environmental Protection Agency (EPA) receives reports of production, imports and exports of SF6 in bulk and inside of electrical equipment. EPA also receives reports of SF6 emissions, consumption and/or related parameters from users of SF6, including manufacturers and users of electrical transmission and distribution equipment, semiconductor manufacturers, and magnesium producers and processers. Based on these reports, EPA estimates the consumption of SF6 by each industry, including facilities that do not report to the GHGRP. In this paper, we compare the consumption estimated based on reports from SF6 suppliers (producers, importers and exporters) to the consumption estimated based on reports from SF6 users, discussing differences and possible reasons for them. We find that in the one year studied, 2012, consumption based on reports from users accounted for 59% of the consumption based on reports from suppliers. We conclude that the uncertainties associated with the consumption estimates are not likely to explain this difference, and that there may be significant uses of SF6 in the US other than manufacturing and use of electrical equipment, semiconductor manufacturing, and magnesium production and processing.

Reducing SF6 emissions from electrical switchgear

SF6 is a greenhouse gas applied in particular in electrical switchgear for the transmission and distribution of energy. It is indispensable for this purpose because of its superior electrical properties at high voltage. The consequent handling of SF6 and the continuous effort to reduce leakage from electrical switchgear by design and material has reduced and will further reduce emissions of SF6. Taking the German SF6 emission data reported annually, the authors tried to relate local emission data from several sources – not only electrical switchgear – with globally reported and measured SF6 concentrations. The latest revision of the European F-gas regulation, EU 517/2014, imposes the requirement on users to either perform regular leak search or install leakage detection systems on switchgear in service containing more than 6 kg of SF6. International switchgear standards pose limits on the leakage rate of equipment and prescribe routine tests before delivery. The paper presents several possibilities to reduce the SF6 emission from switchgear by design and choice of materials. Another source for emitted gas is the manual handling of SF6. As an example for improved SF6 handling, a “zero” emission automatic test and filling station for hermetically sealed switchgear is evaluated.

Sulfur hexafluoride (SF<sub>6</sub>) emissions in East Asia determined by inverse modeling

Abstract. Sulfur hexafluoride (SF6) has a global warming potential of around 22 800 over a 100-year time horizon and is one of the greenhouse gases regulated under the Kyoto Protocol. Around the year 2000 there was a reversal in the global SF6 emission trend, from a decreasing to an increasing trend, which was likely caused by increasing emissions in countries that are not obligated to report their annual emissions to the United Nations Framework Convention on Climate Change. In this study, SF6 emissions during the period 2006–2012 for all East Asian countries – including Mongolia, China, Taiwan, North Korea, South Korea and Japan – were determined by using inverse modeling and in situ atmospheric measurements. We found that the most important sources of uncertainty associated with these inversions are related to the choice of a priori emissions and their assumed uncertainty, the station network as well as the meteorological input data. Much lower uncertainties are due to seasonal variability in the emissions, inversion geometry and resolution, and the measurement calibration scale. Based on the results of these sensitivity tests, we estimate that the total SF6 emission in East Asia increased rapidly from 2404 ± 325 Mg yr−1 in 2006 to 3787 ± 512 Mg yr−1 in 2009 and stabilized thereafter. China contributed 60–72% to the total East Asian emission for the different years, followed by South Korea (8–16%), Japan (5–16%) and Taiwan (4–7%), while the contributions from North Korea and Mongolia together were less than 3% of the total. The per capita SF6 emissions are highest in South Korea and Taiwan, while the per capita emissions for China, North Korea and Japan are close to global average. During the period 2006–2012, emissions from China and from South Korea increased, while emissions from Taiwan and Japan decreased overall.

SF6 usage and emission trends in the TFT-LCD industry

Several fluorinated compounds (FCs) used in electronics manufacturing, including SF6, perfluorocarbons (PFCs), and hydrofluorocarbons (HFCs) are extremely potent greenhouse gases. These compounds are classified as global warming pollutants to be controlled by the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol. Thin film transistor liquid crystal display (TFT-LCD) manufacturing is a major source of SF6 emissions, in which these gases are used for equipment cleaning and plasma etching. The respective Environmental Protection Administration of the Republic of China, Taiwan and the Environmental Protection Agency of the United States collaboratively strive in encouraging high technology manufacturers to improve annual reporting of FCs emissions and implement emission reduction practices and technologies.In the TFT-LCD industry, FCs account on average for 30% of total greenhouse gas emissions; 80% of emissions originate from the etching process and 20% from the chemical vapor deposition (CVD) chamber cleaning process, which is in compliance with Taiwan EPA data reports from 2005 to 2010. The leading TFT-LCD manufacturers are Japan, Korea, and Taiwan. The World LCD Industry Cooperation Committee (WLICC) subsequently established an aggressive climate protection action plan in 2001. This study focuses specifically on SF6 usage and emission factors reflecting common TFT-LCD manufacturing practices.

Sulfur Hexafluoride (SF6) Emission Estimates for China: An Inventory for 1990–2010 and a Projection to 2020

Sulfur hexafluoride (SF6) is the most potent greenhouse gas regulated under the Kyoto Protocol, with a high global warming potential. In this study, SF6 emissions from China were inventoried for 1990-2010 and projected to 2020. Results reveal that the highest SF6 emission contribution originates from the electrical equipment sector (about 70%), followed by the magnesium production sector, the semiconductor manufacture sector and the SF6 production sector (each about 10%). Both agreements and discrepancies were found in comparisons of our estimates with previously published data. An accelerated growth rate was found for Chinese SF6 emissions during 1990-2010. Because the relative growth rate of SF6 emissions is estimated to be much higher than those of CO2, CH4, and N2O, SF6 will play an increasing role in greenhouse gas emissions in China. Global contributions from China increased rapidly from 0.9 ± 0.3% in 1990 to 22.8 ± 6.3% in 2008, making China one of the crucial contributors to the recent growth in global emissions. Under the examined Business-as-usual (BAU) Scenario, projected emissions will reach 4270 ± 1020 t in 2020, but a reduction of about 90% of the projected BAU emissions would be obtained under the Alternative Scenario.

Environmental evaluation of power transmission in Norway

Electrical grid systems are required as a consequence of energy not being produced in the same place as it is consumed, and they are a key element of our energy systems. Transmission and distribution assets comprised of power lines, cables, transformers, substations and other electrical equipment generate a wide range of environmental impacts. Throughout the lifetime of the equipment, the impacts originate mainly from power losses during the use phase, but other life cycle stages such as installation, maintenance and dismantling also contribute significantly to some impact categories. In this paper, the environmental impacts of the Norwegian transmission grid are assessed. The methodology used here is Life Cycle Assessment (LCA) with ReCiPe as impact assessment method. In total, 11,097km of lines and cables, 345 transformers and 121 substations were installed in the Norwegian transmission grid by the end of 2009; the network also included some hundreds of kilometers of sea cables between Norway and abroad. The results show that for each kWh of electricity transmitted in Norway, climate change impacts are of 1.3–1.5gCO2eq., assuming a Norwegian electricity mix. Half of these emissions are associated with power losses, and the other half with infrastructure processes such as materials production, installation, maintenance, and end-of-life. The results also show that after the losses, the infrastructure processes for overhead lines and transformers, and the emissions of SF6 from Gas Insulated equipment are the most relevant contributors for total climate impacts. A sensitivity analysis is done with respect to the electricity mix used to model power losses in the system. The results show that the contribution of power losses to the total climate change scores increases to 84% and 94%, by replacing the Norwegian mix by the Nordic mix and the European mix, respectively.

TransCom model simulations of CH<sub>4</sub> and related species: linking transport, surface flux and chemical loss with CH<sub>4</sub> variability in the troposphere and lower stratosphere

Abstract. A chemistry-transport model (CTM) intercomparison experiment (TransCom-CH4) has been designed to investigate the roles of surface emissions, transport and chemical loss in simulating the global methane distribution. Model simulations were conducted using twelve models and four model variants and results were archived for the period of 1990–2007. All but one model transports were driven by reanalysis products from 3 different meteorological agencies. The transport and removal of CH4 in six different emission scenarios were simulated, with net global emissions of 513 ± 9 and 514 ± 14 Tg CH4 yr−1 for the 1990s and 2000s, respectively. Additionally, sulfur hexafluoride (SF6) was simulated to check the interhemispheric transport, radon (222Rn) to check the subgrid scale transport, and methyl chloroform (CH3CCl3) to check the chemical removal by the tropospheric hydroxyl radical (OH). The results are compared to monthly or annual mean time series of CH4, SF6 and CH3CCl3 measurements from 8 selected background sites, and to satellite observations of CH4 in the upper troposphere and stratosphere. Most models adequately capture the vertical gradients in the stratosphere, the average long-term trends, seasonal cycles, interannual variations (IAVs) and interhemispheric (IH) gradients at the surface sites for SF6, CH3CCl3 and CH4. The vertical gradients of all tracers between the surface and the upper troposphere are consistent within the models, revealing vertical transport differences between models. An average IH exchange time of 1.39 ± 0.18 yr is derived from SF6 time series. Sensitivity simulations suggest that the estimated trends in exchange time, over the period of 1996–2007, are caused by a change of SF6 emissions towards the tropics. Using six sets of emission scenarios, we show that the decadal average CH4 growth rate likely reached equilibrium in the early 2000s due to the flattening of anthropogenic emission growth since the late 1990s. Up to 60% of the IAVs in the observed CH4 concentrations can be explained by accounting for the IAVs in emissions, from biomass burning and wetlands, as well as meteorology in the forward models. The modeled CH4 budget is shown to depend strongly on the troposphere-stratosphere exchange rate and thus on the model's vertical grid structure and circulation in the lower stratosphere. The 15-model median CH4 and CH3CCl3 atmospheric lifetimes are estimated to be 9.99 ± 0.08 and 4.61 ± 0.13 yr, respectively, with little IAV due to transport and temperature.

Improving measurements of SF<sub>6</sub> for the study of atmospheric transport and emissions

Abstract. Sulfur hexafluoride (SF6) is a potent greenhouse gas and useful atmospheric tracer. Measurements of SF6 on global and regional scales are necessary to estimate emissions and to verify or examine the performance of atmospheric transport models. Typical precision for common gas chromatographic methods with electron capture detection (GC-ECD) is 1–2%. We have modified a common GC-ECD method to achieve measurement precision of 0.5% or better. Global mean SF6 measurements were used to examine changes in the growth rate of SF6 and corresponding SF6 emissions. Global emissions and mixing ratios from 2000–2008 are consistent with recently published work. More recent observations show a 10% decline in SF6 emissions in 2008–2009, which seems to coincide with a decrease in world economic output. This decline was short-lived, as the global SF6 growth rate has recently increased to near its 2007–2008 maximum value of 0.30±0.03 pmol mol−1 (ppt) yr−1 (95% C.L.).

Atmospheric variability and emissions of halogenated trace gases near New York City

Abstract Elevated mixing ratios of chlorofluorocarbons (CFC-11 and CFC-12), and sulfur hexafluoride (SF6) have been observed at Lamont-Doherty Earth Observatory (LDEO), located approximately 25 km north of New York City (NYC). Emissions and transport of these gases are of interest because of their global warming potential, the role of CFCs in depletion of stratospheric ozone and information they provide on the transport of atmospheric pollutants. Comparison of trace gas time series with meteorological data indicates that both NYC and the region to the southwest (New Jersey and the Philadelphia –Washington DC area) are significant sources of CFCs, and confirms that NYC is an unusually large source of SF6. From 1996 to 2005 the elevation of CFC-12 mixing ratio above that of the remote (well mixed) atmosphere has decreased on average by 5.2 ± 0.6 ppt y−1, whereas that of CFC-11 has not changed significantly (0.0 ± 2.0 ppt y−1). From 1998 to 2006, the elevation of SF6 mixing ratios above that of the remote atmosphere declined by 0.4 ± 0.1 ppt y−1. Time series of the same gases measured at Harvard Forest, 205 km northeast of LDEO, demonstrate transport of air masses with elevated levels of these gases from their source region to central Massachusetts. Emissions in the local area around LDEO were quantified through analysis of diurnal cycles. Local CFC-12 emissions decreased ca. 95% between 1996 and 2005 while CFC-11 emission decreased ca. 51% during the same period. Local SF6 emissions decreased by 47% between 1998 and 2005.

Inversion of long-lived trace gas emissions using combined Eulerian and Lagrangian chemical transport models

Abstract. We present a method for estimating emissions of long-lived trace gases from a sparse global network of high-frequency observatories, using both a global Eulerian chemical transport model and Lagrangian particle dispersion model. Emissions are derived in a single step after determining sensitivities of the observations to initial conditions, the high-resolution emissions field close to observation points, and larger regions further from the measurements. This method has the several advantages over inversions using one type of model alone, in that: high-resolution simulations can be carried out in limited domains close to the measurement sites, with lower resolution being used further from them; the influence of errors due to aggregation of emissions close to the measurement sites can be minimized; assumptions about boundary conditions to the Lagrangian model do not need to be made, since the entire emissions field is estimated; any combination of appropriate models can be used, with no code modification. Because the sensitivity to the entire emissions field is derived, the estimation can be carried out using traditional statistical methods without the need for multiple steps in the inversion. We demonstrate the utility of this approach by determining global SF6 emissions using measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) between 2007 and 2009. The global total and large-scale patterns of the derived emissions agree well with previous studies, whilst allowing emissions to be determined at higher resolution than has previously been possible, and improving the agreement between the modeled and observed mole fractions at some sites.

High increase of global F-gas emissions until 2050

Emissions of fluorinated greenhouse gases (GHGs) (hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphurhexafluoride (SF6)) have increased significantly in recent years and are estimated to rise further. Banks and emissions of HFCs, PFCs and SF6 in the year 2050 are projected per sector in a business-as-usual scenario. The total global emissions of fluorinated GHGs will amount to 4 GT CO2 eq. by 2050 if no mitigation measures are taken. The contribution of F-gases to global warming will increase from approx. 1.3% (2004) to 7.9% of projected total anthropogenic CO2 emissions in this business-as-usual scenario in 2050. For significant reductions in future emissions of Kyoto F-gases, additional efforts from both developed and developing countries are needed.

History of atmospheric SF<sub>6</sub> from 1973 to 2008

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.

Greenhouse gas relationships in the Indian summer monsoon plume measured by the CARIBIC passenger aircraft

Abstract. During the Indian summer monsoon period 2008, regular measurement flights were performed by the CARIBIC aircraft between Germany and India. Measurements included whole air sampling and subsequent analysis for greenhouse gases (CH4, CO2, N2O, SF6) and in-situ measurements of CO, O3, and H2O. For all these tracers a distinct monsoon signature was observed in the longitude range 50–80° E south of 40° N at flight altitudes 8–12.5 km. The formation of a monsoon plume with enhanced mixing ratios was observed for CH4, N2O, SF6, CO and H2O. The plume began to develop in May and persisted through September, and maximum mixing ratios and maximum spatial extension of the plume were observed in August. For CO2 and O3 a minimum was observed. The amplitude of the CO2 seasonal cycle was larger than at comparable latitudes outside the monsoon region, and the CO2 spring maximum was observed with a delay of one month. Different tracer relationships show strong spatial variations across the plume. The comparison with NOAA ground station data shows a clear enhancement for CH4, N2O, SF6 and CO and a decrease in CO2 mixing ratios. Assuming seasonally invariant SF6 emissions based on the EDGAR 4.0 inventory, monthly emissions were estimated for the period June–September for CH4, N2O, and CO, and the CO2 uptake was estimated. While for N2O an emission decrease during the monsoon period was derived, emissions of CH4 were highest in September indicating a different seasonal cycle of emissions. Net CO2 uptake by the vegetation was largest in September.

The global SF<sub>6</sub> source inferred from long-term high precision atmospheric measurements and its comparison with emission inventories

Abstract. Emissions of sulphur hexafluoride (SF6), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (estimated as 800 to 3200 years), the accumulation of SF6 in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF6 observations shows an increase in SF6 abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF6 decreased after 1995, most likely due to SF6 emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF6 source leaves a surprisingly large gap of more than 70–80% of non-reported SF6 emissions in the last decade. This suggests a strong under-estimation of emissions in Annex I countries and underlines the urgent need for independent atmospheric verification of greenhouse gases emissions accounting.

NF3, the greenhouse gas missing from Kyoto

Nitrogen trifluoride (NF3) can be called the missing greenhouse gas: It is a synthetic chemical produced in industrial quantities; it is not included in the Kyoto basket of greenhouse gases or in national reporting under the United Nations Framework Convention on Climate Change (UNFCCC); and there are no observations documenting its atmospheric abundance. Current publications report a long lifetime of 740 yr and a global warming potential (GWP), which in the Kyoto basket is second only to SF6. We re‐examine the atmospheric chemistry of NF3 and calculate a shorter lifetime of 550 yr, but still far beyond any societal time frames. With 2008 production equivalent to 67 million metric tons of CO2, NF3 has a potential greenhouse impact larger than that of the industrialized nations' emissions of PFCs or SF6, or even that of the world's largest coal‐fired power plants. If released, annual production would increase the lower atmospheric abundance by 0.4 ppt, and it is urgent to document NF3 emissions through atmospheric observations.