Reversal of global atmospheric ethane and propane trends largely due to US oil and natural gas production

Journal name:
Nature Geoscience
Volume:
9,
Pages:
490–495
Year published:
DOI:
doi:10.1038/ngeo2721
Received
Accepted
Published online

Non-methane hydrocarbons such as ethane are important precursors to tropospheric ozone and aerosols. Using data from a global surface network and atmospheric column observations we show that the steady decline in the ethane mole fraction that began in the 1970s1, 2, 3 halted between 2005 and 2010 in most of the Northern Hemisphere and has since reversed. We calculate a yearly increase in ethane emissions in the Northern Hemisphere of 0.42 (±0.19)Tgyr−1 between mid-2009 and mid-2014. The largest increases in ethane and the shorter-lived propane are seen over the central and eastern USA, with a spatial distribution that suggests North American oil and natural gas development as the primary source of increasing emissions. By including other co-emitted oil and natural gas non-methane hydrocarbons, we estimate a Northern Hemisphere total non-methane hydrocarbon yearly emission increase of 1.2 (±0.8)Tgyr−1. Atmospheric chemical transport modelling suggests that these emissions could augment summertime mean surface ozone by several nanomoles per mole near oil and natural gas production regions. Methane/ethane oil and natural gas emission ratios could suggest a significant increase in associated methane emissions; however, this increase is inconsistent with observed leak rates in production regions and changes in methane’s global isotopic ratio.

At a glance

Figures

  1. Histories of atmospheric ethane.
    Figure 1: Histories of atmospheric ethane.

    a, Reconstructed 1950–2010 ethane history from firn air sampling at NEEM in Greenland3 with 2009.5 mean seasonally detrended atmospheric values at five Arctic sites for comparison. Data from ref. 3. b, Ten years of NMHC flask network data in south Iceland. Individual flask data, identified outliers (smaller blue points), a smoothed fit, the trend results after removal of harmonic components, and the linear regression fit are shown, with a 46.2pmolmol−1yr−1 increase from 2009.5 to 2014.5. c,d, Ethane upper troposphere and lower stratosphere (UTLS), and mid troposphere FTIR columns showing a trend reversal and increasing rate of change after 2009 at Jungfraujoch, Switzerland (c), in contrast to Lauder, New Zealand (d). e, Monthly running median data from the daily in situ record at Hohenpeissenberg, with smoothed, function, and trend fits. A polynomial fit shows a minimum in the second half of 2009; the linear regression to the post 2009.5 trend curves and seasonal maxima and minima show increases of 22–23pmolmol−1yr−1.

  2. Latitudinal distribution of ethane, propane, iso-butane, and n-butane.
    Figure 2: Latitudinal distribution of ethane, propane, iso-butane, and n-butane.

    These representations of surface mole fractions were generated using weekly data from 37 to 39 global background monitoring sites, altogether some 30,000 data points for each graph. Note that these plots are a representation of latitudinal averages of atmospheric mole fractions; therefore, they do not capture differences between continents at the same latitude. Procedures for data filtering and processing are discussed in the Methods.

  3. Ethane and propane trends at global monitoring sites.
    Figure 3: Ethane and propane trends at global monitoring sites.

    Mole fraction changes are indicated by the colour scale with marker size corresponding to the R2 of the fit multiplied by the fraction of available site data. Results from overlapping GGGRN flask and in situ measurements are shown in black rectangles for Summit and Hohenpeissenberg. a, Increasing ethane is observed throughout the NH, with the strongest signal in North America, the North Atlantic, and neighbouring continents. There is no or very little change in ethane at SH sites. b, Propane shows a more pronounced region of increasing mole fractions in the eastern USA and at nearby downwind sites. Again, these changes are not seen at the SH sites.

  4. Ozone sensitivity study.
    Figure 4: Ozone sensitivity study.

    Estimate for the average annual 2009.5–2014.5 June–August change in surface ozone from a 4.2%yr−1 NH increase in ethane, and inferred emission increases in propane, butane and pentane isomers from USA O&NG sources. The modelling did not consider increases in methane and NMHC > C5 emissions, and assumed constant emissions of nitrogen oxides and volatile organic compounds from other emission sectors. Increases in surface ozone are predicted over extended areas of the USA and downwind.

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Author information

Affiliations

  1. Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80305, USA

    • Detlev Helmig,
    • Samuel Rossabi &
    • Jacques Hueber
  2. Earth Systems Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80305, USA

    • Pieter Tans,
    • Stephen A. Montzka,
    • Ken Masarie &
    • Kirk Thoning
  3. Deutscher Wetterdienst, 82383 Hohenpeissenberg, Germany

    • Christian Plass-Duelmer &
    • Anja Claude
  4. Wolfson Atmospheric Chemistry Laboratories, University of York, York YO10 5DD, UK

    • Lucy J. Carpenter &
    • Shalini Punjabi
  5. National Centre for Atmospheric Science, University of York, York YO10 5DD, UK

    • Alastair C. Lewis
  6. Laboratory for Air Pollution and Environmental Technology, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Duebendorf, Switzerland

    • Stefan Reimann &
    • Martin K. Vollmer
  7. Karlsruhe Institute for Technology, Campus Alpine, 82467 Garmisch-Partenkirchen, Germany

    • Rainer Steinbrecher
  8. National Center for Atmospheric Research, Boulder, Colorado 80301, USA

    • James W. Hannigan &
    • Louisa K. Emmons
  9. Institute of Astrophysics and Geophysics, University of Liège, 4000 Liège, Belgium

    • Emmanuel Mahieu &
    • Bruno Franco
  10. National Institute of Water and Atmospheric Research, Lauder 9352, New Zealand

    • Dan Smale
  11. Max Planck Institute for Chemistry, 55128 Mainz, Germany

    • Andrea Pozzer

Contributions

D.H., study design, global flask network operation, Summit in situ measurements, data analyses, quality control, site comparisons, manuscript preparation. S.R., data processing, preparation of graphs, manuscript preparation. J.H., global flask network operation, analytical work, Summit in situ measurements. P.T., global flask network operation, manuscript preparation. S.A.M., propane data from the North American Tower flask programme and its quality control, manuscript preparation. K.M., NOAA network data management, NMHC global graphs shown in Fig. 2, manuscript preparation. K.T., data filtering, trend analyses, data statistics, manuscript preparation. C.P.-D., HPB NMHC monitoring, flask–in situ comparisons, manuscript preparation. A.C., HPB in situ NMHC monitoring. A.C.L., CVO NMHC in situ observations, manuscript preparation. L.J.C., CVO NMHC in situ observations, manuscript preparation. S.P., CVO NMHC in situ observations. S.R., JFJ NMHC in situ observations. M.K.V., JFJ NMHC in situ observations, manuscript preparation. R.S., VOC World Calibration Center, NMHC quality control, manuscript preparation. J.W.H., FTIR data evaluations and coordination, manuscript preparation. L.K.E., emissions modelling, ethane inventory data, manuscript preparation. E.M., JFJ FTIR data processing and analyses, manuscript preparation. B.F., JFJ FTIR data processing and analyses, manuscript preparation. D.S., Lauder FTIR observations and data processing, manuscript preparation. A.P., ethane inventory data, photochemical ozone modelling, manuscript preparation.

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The authors declare no competing financial interests.

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