Jens Mühle

Medusa: A Sample Preconcentration and GC/MS Detector System for in Situ Measurements of Atmospheric Trace Halocarbons, Hydrocarbons, and Sulfur Compounds

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 CH(3)CF(3)) and hydrofluorocarbons (HFCs, e.g., CH(3)CF(3)) to the higher-boiling point solvents (such as CH(3)Cl(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). This 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.

Emissions of halogenated compounds in East Asia determined from measurements at Jeju Island, Korea.

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.

Recent and future trends in synthetic greenhouse gas radiative forcing

Natural Environment Research Council (Great Britain) (Advanced Research Fellowship NE/I021365/1)

Role of atmospheric oxidation in recent methane growth

Significance Methane, the second most important greenhouse gas, has varied markedly in its atmospheric growth rate. The cause of these fluctuations remains poorly understood. Recent efforts to determine the drivers of the pause in growth in 1999 and renewed growth from 2007 onward have focused primarily on changes in sources alone. Here, we show that changes in the major methane sink, the hydroxyl radical, have likely played a substantial role in the global methane growth rate. This work has significant implications for our understanding of the methane budget, which is important if we are to better predict future changes in this potent greenhouse gas and effectively mitigate enhanced radiative forcing caused by anthropogenic emissions. The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH4 sink, in the recent CH4 growth. We also examine the influence of systematic uncertainties in OH concentrations on CH4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH3CCl3), which is lost primarily through reaction with OH, to estimate OH levels as well as CH3CC3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH4 emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH4 emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13CH4/12CH4 ratio and the recent growth in C2H6. Our approach indicates that significant OH-related uncertainties in the CH4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH4 emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered.

Reconciling reported and unreported HFC emissions with atmospheric observations

Significance 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. 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.

Sulfuryl fluoride in the global atmosphere

United States. National Aeronautics and Space Administration (NASA) (Upper Atmospheric Research Program)

Nitrogen trifluoride global emissions estimated from updated atmospheric measurements

Nitrogen trifluoride (NF3) 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 NF3 in 2011 were 1.18 ± 0.21 Gg⋅y−1, or ∼20 Tg CO2-eq⋅y−1 (carbon dioxide equivalent emissions based on a 100-y global warming potential of 16,600 for NF3). 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−2 over the prior decade. In terms of CO2 equivalents, current NF3 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 NF3 over hexafluoroethane (C2F6) in electronics manufacture is significant—emissions of between 53 and 220 Tg CO2-eq⋅y−1 were avoided during 2011. Despite these savings, total NF3 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 NF3 emissions reduction strategies to keep pace with its increasing use and to slow its rising contribution to anthropogenic climate forcing.

Biomass burning and fossil fuel signatures in the upper troposphere observed during a CARIBIC flight from Namibia to Germany

During a CARIBIC flight from Namibia to Germany in July 2000, air influenced by recent convective injection of biomass burning emissions was intersected in the vicinity of the ITCZ at an altitude of 10 km. The observed CO enhancement ratios for non-methane hydrocarbons (NMHCs) and methyl halides are consistent with those reported for fresh biomass burning plumes. Air masses affected by transcontinental transport of natural gas emissions, most probably from the Gulf of Mexico, were encountered over the Mediterranean Sea. These are one of the few observations of deep convection of biomass burning emissions to the upper troposphere and of long range transport of natural gas emissions reported so far. The observations demonstrate the importance of deep convection for the chemistry of the upper troposphere and the potential of commercial aircraft for atmospheric research.

Trace gas and radical diurnal behavior in the marine boundary layer during INDOEX 1999

Arabia causing, for instance, a reduction in j(O( 1 D)) by up to 40%. The diurnal behavior of the trace gases and parameters in the MBL has been investigated by using a timedependent zero-dimensional chemical model. Significant differences between the diurnal behavior of RO* 2 derived from the model and observed in measurements were identified. The measured HCHO concentrations differed from the model results and are best explained by some missing chemistry involving low amounts of Cl. Other possible processes describing these two effects are presented and discussed. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); KEYWORDS: peroxy radicals, INDOEX, chlorine, nonmethane hydrocarbons, photolysis frequencies, formaldehyde

Australian carbon tetrachloride emissions in a global context

Environmental context Carbon tetrachloride in the background atmosphere is a significant environmental concern, responsible for ~10% of observed stratospheric ozone depletion. Atmospheric concentrations of CCl4 are higher than expected from currently identified emission sources: largely residual emissions from production, transport and use. Additional sources are required to balance the expected atmospheric destruction of CCl4 and may contribute to a slower-than-expected recovery of the Antarctic ozone ‘hole’. Abstract Global (1978–2012) and Australian (1996–2011) carbon tetrachloride emissions are estimated from atmospheric observations of CCl4 using data from the Advanced Global Atmospheric Gases Experiment (AGAGE) global network, in particular from Cape Grim, Tasmania. Global and Australian emissions are in decline in response to Montreal Protocol restrictions on CCl4 production and consumption for dispersive uses in the developed and developing world. However, atmospheric data-derived emissions are significantly larger than ‘bottom-up’ estimates from direct and indirect CCl4 production, CCl4 transportation and use. Australian CCl4 emissions are not a result of these sources, and the identification of the origin of Australian emissions may provide a clue to the origin of some of these ‘missing’ global sources.