Project Scientist

Research Interests:

  • AGAGE (Advanced Global Atmospheric Gases Experiment) http://agage.eas.gatech.edu/
  • Greenhouse gases
  • Halogenated trace gases
  • Ozone depleting compounds
  • Trace gas measurements (especially GC-FID/ECD/MSD)
  • Global warming
  • Top-down (measurement based) verification of bottom-up emission estimates
  • Atmospheric chemistry
  • Wildfire emissions
  • Long-range transport of pollutants

Degrees:

  • Diploma in Chemistry, University of Wuppertal
  • Doctor of Natural Sciences, Max Planck Institute for Chemistry, Mainz and Johannes Gutenberg University Mainz

Recent Publications

Simmonds, PG, Rigby M, Manning AJ, Lunt MF, O'Doherty S, McCulloch A, Fraser PJ, Henne S, Vollmer MK, Mühle J, Weiss RF, Salameh PK, Young D, Reimann S, Wenger A, Arnold T, Harth CM, Krummel PB, Steele LP, Dunse BL, Miller BR, Lunder CR, Hermansen O, Schmidbauer N, Saito T, Yokouchi Y, Park S, Li S, Yao B, Zhou LX, Arduini J, Maione M, Wang RHJ, Ivy D, Prinn RG.  2016.  Global and regional emissions estimates of 1,1-difluoroethane (HFC-152a, CH3CHF2) from in situ and air archive observations. Atmospheric Chemistry and Physics. 16:365-382.: Copernicus Publications AbstractWebsite
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Chirkov, M, Stiller GP, Laeng A, Kellmann S, von Clarmann T, Boone CD, Elkins JW, Engel A, Glatthor N, Grabowski U, Harth CM, Kiefer M, Kolonjari F, Krummel PB, Linden A, Lunder CR, Miller BR, Montzka SA, Mühle J, O'Doherty S, Orphal J, Prinn RG, Toon G, Vollmer MK, Walker KA, Weiss RF, Wiegele A, Young D.  2016.  Global HCFC-22 measurements with MIPAS: retrieval, validation, global distribution and its evolution over 2005–2012. Atmospheric Chemistry and Physics. 16:3345-3368.: Copernicus Publications AbstractWebsite
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Simmonds, PG, Rigby M, Manning AJ, Lunt MF, O'Doherty S, McCulloch A, Fraser PJ, Henne S, Vollmer MK, Muhle J, Weiss RF, Salameh PK, Young D, Reimann S, Wenger A, Arnold T, Harth CM, Krummel PB, Steele LP, Dunse BL, Miller BR, Lunder CR, Hermansen O, Schmidbauer N, Saito T, Yokouchi Y, Park S, Li S, Yao B, Zhou LX, Arduini J, Maione M, Wang RHJ, Ivy D, Prinn RG.  2016.  Global and regional emissions estimates of 1,1-difluoroethane (HFC-152a, CH3CHF2) from in situ and air archive observations. Atmospheric Chemistry and Physics. 16:365-382. AbstractWebsite

High frequency, in situ observations from 11 globally distributed sites for the period 1994-2014 and archived air measurements dating from 1978 onward have been used to determine the global growth rate of 1,1-difluoroethane (HFC-152a, CH3CHF2). These observations have been combined with a range of atmospheric transport models to derive global emission estimates in a top-down approach. HFC-152a is a greenhouse gas with a short atmospheric lifetime of about 1.5 years. Since it does not contain chlorine or bromine, HFC-152a makes no direct contribution to the destruction of stratospheric ozone and is therefore used as a substitute for the ozone de- pleting chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). The concentration of HFC-152a has grown substantially since the first direct measurements in 1994, reaching a maximum annual global growth rate of 0.84 +/- 0.05 ppt yr(-1) in 2006, implying a substantial increase in emissions up to 2006. However, since 2007, the annual rate of growth has slowed to 0.38 +/- 0.04 ppt yr(-1) in 2010 with a further decline to an annual average rate of growth in 2013-2014 of -0.06 +/- 0.05 ppt yr(-1). The annual average Northern Hemisphere (NH) mole fraction in 1994 was 1.2 ppt rising to an annual average mole fraction of 10.1 ppt in 2014. Average annual mole fractions in the Southern Hemisphere (SH) in 1998 and 2014 were 0.84 and 4.5 ppt, respectively. We estimate global emissions of HFC-152a have risen from 7.3 +/- 5.6 Gg yr(-1) in 1994 to a maximum of 54.4 +/- 17.1 Gg yr(-1) in 2011, declining to 52.5 +/- 20.1 Gg yr(-1) in 2014 or 7.2 +/- 2.8 Tg-CO2 eq yr(-1). Analysis of mole fraction enhancements above regional background atmospheric levels suggests substantial emissions from North America, Asia, and Europe. Global HFC emissions (so called "bottom up" emissions) reported by the United Nations Framework Convention on Climate Change (UNFCCC) are based on cumulative national emission data reported to the UNFCCC, which in turn are based on national consumption data. There appears to be a significant underestimate (> 20 Gg) of "bottom-up" reported emissions of HFC-152a, possibly arising from largely underestimated USA emissions and undeclared Asian emissions.

Deeds, DA, Kulongoski JT, Mühle J, Weiss RF.  2015.  Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: Observations in groundwaters along the San Andreas Fault. Earth and Planetary Science Letters. 412:163-172. AbstractWebsite

Abstract Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge ( C r e ; ∼30 fmol kg−1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1–9 times C r e ), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10–980 times C r e ) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20–100 km) suggests that the SAFS potentially emits ( 0.3 – 1 ) × 10 − 1 kg CF4 yr−1 to the Earth's surface. For comparison, the chemical weathering of ∼ 7.5 × 10 4 km 2 of granitic rock in California is estimated to release ( 0.019 – 3.2 ) × 10 − 1 kg CF4 yr−1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial–interglacial transitions.

Dlugokencky, EJ, Hall BD, Montzka SA, Dutton G, Mühle J, Elkins JW.  2015.  [Global Climate, Atmospheric chemical composition] Long-lived greenhouse gases [in State of the Climate in 2014]. Bulletin of the American Meteorological Society. 96( Blunden J, Arndt DS, Eds.).:S39-S42. Abstract
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Johnson, TL, Brahamsha B, Palenik B, Mühle J.  2015.  Halomethane production by vanadium-dependent bromoperoxidase in marine Synechococcus. Limnology and Oceanography. 60:1823-1835. AbstractWebsite

To investigate the role of vanadium-dependent bromoperoxidase (VBPO) for the production of halogenated methanes in marine prokaryotes, we measured VBPO activity and halomethane production in two strains of Synechococcus; one with VBPO (strain CC9311) and one without VBPO (strain WH8102). A mutant strain of CC9311, VMUT2, in which the gene for VBPO is disrupted, was also tested. A suite of halomethanes was measured in the headspace above cultures as well as in the culture medium with a purge-and-trap method. Monohalomethanes were the most consistently produced molecules among the three strains tested. Additionally, CC9311 produced 301 ± 109 molecules cell−1 d−1 of bromoform (CHBr3) when VBPO activity was detected, while production was not significantly different from zero when VBPO activity was not detected. VBPO activity and CHBr3 production were only detected when cultures of CC9311 were stirred, which may contribute to the often moderate to weak correlations between CHBr3 concentration and biological markers in the ocean. No production was seen by VMUT2 or WH8102. These data show that CHBr3 production rates are dramatically increased with or exclusive to the presence of VBPO, supporting its involvement in CHBr3 synthesis. This study thus provides genetic evidence that certain strains of marine Synechococcus, under particular conditions, can be a natural source of marine CHBr3, which contributes to ozone depletion in the stratosphere.