B. R. Greally

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.

Global trends, seasonal cycles and European emissions of dichloromethane, trichloroethene and tetrachloroethene from the AGAGE observations at Mace Head, Ireland and Cape Grim, Tasmania

[1] In situ observations (every 4 hours) of dichloromethane (CH 2 Cl 2 ) from April 1995 to December 2004 and trichloroethene (C 2 HCl 3 ) and tetrachloroethene (C 2 Cl 4 ) from September 2000 to December 2004 are reported for the Advanced Global Atmospheric Gases Experiment (AGAGE) station at Mace Head, Ireland. At a second AGAGE station at Cape Grim, Tasmania, CH 2 Cl 2 and C 2 Cl 4 data collection commenced in 1998 and 2000, respectively. C 2 HCl 3 is below the limit of detection at Cape Grim except during pollution episodes. At Mace Head CH 2 Cl 2 shows a downward trend from 1995 to 2004 of 0.7±0.2 ppt yr -1 (ppt: expressed as dry mole fractions in 10 12 ), although from 1998 to 2004 the decrease has been only 0.3 ± 0.1ppt yr -1 . Conversely, there has been a small but significant growth of 0.05 ± 0.01 ppt yr -1 in CH 2 Cl 2 at Cape Grim. The time series for C 2 HCl 3 and C 2 Cl 4 are relatively short for accurate trend analyses; however, we observe a small but significant decline in C 2 Cl 4 (0.18 ± 0.05 ppt yr -1 ) at Mace Head. European emissions inferred from AGAGE measurements are compared to recent estimates from industry data and show general agreement for C 2 HCl 3 . Emissions estimated from observations are lower than industry emission estimates for C 2 Cl 4 and much lower in the case of CH 2 Cl 2 . A study of wildfires in Tasmania, uncontaminated by urban emissions, suggests that the biomass burning source of CH 2 Cl 2 may have been previously overestimated. All three solvents have distinct annual cycles, with the phases and amplitudes reflecting their different chemical reactivity with OH as the primary sink.

Low European methyl chloroform emissions inferred from long-term atmospheric measurements

Methyl chloroform (CH3CCl3, 1,1,1,-trichloroethane) was used widely as a solvent before it was recognized to be an ozone-depleting substance and its phase-out was introduced under the Montreal Protocol. Subsequently, its atmospheric concentration has declined steadily and recent European methyl chloroform consumption and emissions were estimated to be less than 0.1 gigagrams per year. However, data from a short-term tropospheric measurement campaign (EXPORT) indicated that European methyl chloroform emissions could have been over 20 gigagrams in 2000 (ref. 6), almost doubling previously estimated global emissions. Such enhanced emissions would significantly affect results from the CH3CC13 method of deriving global abundances of hydroxyl radicals (OH) (refs 7–12)—the dominant reactive atmospheric chemical for removing trace gases related to air pollution, ozone depletion and the greenhouse effect. Here we use long-term, high-frequency data from Mace Head, Ireland and Jungfraujoch, Switzerland, to infer European methyl chloroform emissions. We find that European emission estimates declined from about 60 gigagrams per year in the mid-1990s to 0.3–1.4 and 1.9–3.4 gigagrams per year in 2000–03, based on Mace Head and Jungfraujoch data, respectively. Our European methyl chloroform emission estimates are therefore higher than calculated from consumption data, but are considerably lower than those derived from the EXPORT campaign in 2000 (ref. 6).

Sulfuryl fluoride in the global atmosphere

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

Improved continuous in situ measurements of C 1 -C 3 PFCs, HFCs, HCFCs, CFCs and SF 6 in Europe and Australia

Abstract Improved monitoring of non-CO2 greenhouse gases in air samples is presented, achieved using a new analytical system based on preconcentration, gas-chromatography and mass spectrometry. In addition to the major HFCs, HCFCs and CFCs, the new observations include the first in situ time series of the C1–C3 PFCs (CF4, C2F6 and C3F8) and the more volatile of the HFCs (CHF3, CH2F2, CH3CF3) alongside SF6, all of which are now monitored routinely as part of the Advanced Global Atmospheric Gases Experiment (AGAGE). Observed trends in newly monitored species are shown, obtained from 1–2 years continuous in situ air analyses at remote monitoring sites at Mace Head (Ireland) and Cape Grim (Australia). Observed deviations in the air background for these gas species are linked to modelled trajectories of air masses arriving at the monitoring stations to indicate potential source regions for emissions in Europe and Australia. In addition, preliminary estimates of 2004 mixing ratio growth rates of compounds are deduced from the observations, which highlight the importance of continuous atmospheric monitoring for verification of consumption-based emission estimates of non-CO2 greenhouse gases.

Separation of mixed halocarbons of environmental interest on a new type of silica-based porous-layer open tubular capillary gas chromatographic column

A new type of capillary porous-layer open tubular (PLOT) column consisting of a hydrophobic silica layer on a fused-silica capillary has been tested for the separation of a mixture of environmentally sensitive halocarbons present in tropospheric air. The column shows high retention for a wide range of halocarbons, with elution orders following both boiling point order and hydrogen bonding capability. The resolution of the halocarbons is good and only one pair of halocarbons [CHFClCF3 (HCFC 124) and CH3CF2Cl (HCFC 142b)] cannot be resolved on this column type at all column temperature profiles. Unlike alumina PLOT columns, the silica PLOT column does not dehydrohalogenate labile halocarbons. Excellent reproducibility of retention times and peak areas for halocarbons on the column are reported.

Correction to “Sulfuryl fluoride in the global atmosphere”

[1] In the paper ‘‘Sulfuryl fluoride in the global atmosphere’’ by J. Muhle et al. (Journal of Geophysical Research, 114, D05306, doi:10.1029/2008JD011162, 2009), the final two coauthors were omitted. P. B. Krummel and L. P. Steele are affiliated with Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, D10303, doi:10.1029/2009JD012306, 2009