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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Vollmer, MK, Muhle J, Trudinger CM, Rigby M, Montzka SA, Harth CM, Miller BR, Henne S, Krummel PB, Hall BD, Young D, Kim J, Arduini J, Wenger A, Yao B, Reimann S, O'Doherty S, Maione M, Etheridge DM, Li SL, Verdonik DP, Park S, Dutton G, Steele LP, Lunder CR, Rhee TS, Hermansen O, Schmidbauer N, Wang RHJ, Hill M, Salameh PK, Langenfelds RL, Zhou LX, Blunier T, Schwander J, Elkins JW, Butler JH, Simmonds PG, Weiss RF, Prinn RG, Fraser PJ.  2016.  Atmospheric histories and global emissions of halons H-1211 (CBrClF2), H-1301 (CBrF3), and H-2402 (CBrF2CBrF2). Journal of Geophysical Research-Atmospheres. 121:3663-3686. AbstractWebsite

We report ground-based atmospheric measurements and emission estimates for the halons H-1211 (CBrClF2), H-1301 (CBrF3), and H-2402 (CBrF2CBrF2) from the AGAGE (Advanced Global Atmospheric Gases Experiment) and the National Oceanic and Atmospheric Administration global networks. We also include results from archived air samples in canisters and from polar firn in both hemispheres, thereby deriving an atmospheric record of nearly nine decades (1930s to present). All three halons were absent from the atmosphere until approximate to 1970, when their atmospheric burdens started to increase rapidly. In recent years H-1211 and H-2402 mole fractions have been declining, but H-1301 has continued to grow. High-frequency observations show continuing emissions of H-1211 and H-1301 near most AGAGE sites. For H-2402 the only emissions detected were derived from the region surrounding the Sea of Japan/East Sea. Based on our observations, we derive global emissions using two different inversion approaches. Emissions for H-1211 declined from a peak of 11ktyr(-1) (late 1990s) to 3.9ktyr(-1) at the end of our record (mean of 2013-2015), for H-1301 from 5.4ktyr(-1) (late 1980s) to 1.6ktyr(-1), and for H-2402 from 1.8ktyr(-1) (late 1980s) to 0.38ktyr(-1). Yearly summed halon emissions have decreased substantially; nevertheless, since 2000 they have accounted for approximate to 30% of the emissions of all major anthropogenic ozone depletion substances, when weighted by ozone depletion potentials.

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.

Hossaini, R, Chipperfield MP, Saiz-Lopez A, Harrison JJ, von Glasow R, Sommariva R, Atlas E, Navarro M, Montzka SA, Feng W, Dhomse S, Harth C, Mühle J, Lunder C, O'Doherty S, Young D, Reimann S, Vollmer MK, Krummel PB, Bernath GPFC.  2015.  Growth in stratospheric chlorine from short-lived chemicals not controlled by the Montreal Protocol. Geophysical Research Letters. 42(11):4573-4580. AbstractWebsite

We have developed a chemical mechanism describing the tropospheric degradation of chlorine-containing very short-lived substances (VSLS). The scheme was included in a global atmospheric model and used to quantify the stratospheric injection of chlorine from anthropogenic VSLS (ClyVSLS) between 2005 to 2013. By constraining the model with surface measurements of chloroform (CHCl3), dichloromethane (CH2Cl2), tetrachloroethene (C2Cl4), trichloroethene (C2HCL3) and 1,2-dichloroethane (CH2ClCH2Cl), we infer a 2013 ClyVSLS mixing ratio of 123 parts per trillion (ppt). Stratospheric injection of source gases dominates this supply, accounting for ~83% of the total. The remainder comes from VSLS-derived organic products, phosgene (COCl2, 7%) and formyl chloride (CHClO, 2%), and also hydrogen chloride (HCl, 8%). Stratospheric ClyVSLS increased by ~52% between 2005-2013, with a mean growth rate of 3.7 ppt Cl/yr. This increase is due to recent and ongoing growth in anthropogenic CH – the most abundant chlorinated VSLS not controlled by the Montreal Protocol.

Rhoderick, GC, Hall BD, Harth CM, Kim JS, Lee J, Montzka SA, Mühle J, Reimann S, Vollmer MK, Weiss RF.  2015.  Comparison of halocarbon measurements in an atmospheric dry whole air sample. Elementa: Science of the Anthropocene. 3:1-13. Abstract

The growing awareness of climate change/global warming, and continuing concerns regarding stratospheric ozone depletion, will require continued measurements and standards for many compounds, in particular halocarbons that are linked to these issues. In order to track atmospheric mole fractions and assess the impact of policy on emission rates, it is necessary to demonstrate measurement equivalence at the highest levels of accuracy for assigned values of standards. Precise measurements of these species aid in determining small changes in their atmospheric abundance. A common source of standards/scales and/or well-documented agreement of different scales used to calibrate the measurement instrumentation are key to understanding many sets of data reported by researchers. This report describes the results of a comparison study among National Metrology Institutes and atmospheric research laboratories for the chlorofluorocarbons (CFCs) dichlorodifluoromethane (CFC-12), trichlorofluoromethane (CFC-11), and 1,1,2-trichlorotrifluoroethane (CFC-113); the hydrochlorofluorocarbons (HCFCs) chlorodifluoromethane (HCFC-22) and 1-chloro-1,1-difluoroethane (HCFC-142b); and the hydrofluorocarbon (HFC) 1,1,1,2-tetrafluoroethane (HFC-134a), all in a dried whole air sample. The objective of this study is to compare calibration standards/scales and the measurement capabilities of the participants for these halocarbons at trace atmospheric levels. The results of this study show agreement among four independent calibration scales to better than 2.5% in almost all cases, with many of the reported agreements being better than 1.0%.