Methane and Ethane Total Column Measurements in the Los Angeles Basin

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1 Methane and Ethane Total Column Measurements in the Los Angeles Basin Debra Wunch, Coleen Roehl, Jean-Francois Blavier, Norton Allen, Richard Treffers, Geoffrey Toon, Paul Wennberg AGU Fall Meeting December 3-7, 2012

2 Methane Emissions in the Los Angeles Basin (South Coast Air Basin) Methane emissions in the basin are known to be much higher than estimates from the California Air Resources Board (CARB, Tg/yr) CARB Estimates by Sector Atmospheric Measurements (Wunch et al. 2009) (Hsu et al. 2010) 2008 ARCTAS (Wennberg et al. 2012) 2010 CalNex (Wennberg et al. 2012) CH 4 Emissions (Tg/yr) 0.4 ± ± ± ± 0.1 Hsu et al. (2010), Atmos. Environ., doi: /j.atmosenv ; Wennberg et al. (2012), Environ. Sci. & Tech., doi: /es301138y.

3 Methane (CH 4 ) Emissions Methane can come from: cows, landfills, water treatment plants natural seeps, petroleum industry, natural gas How do we find the source of the excess methane?

4 Ethane (C 2 H 6 ) Emissions Ethane emissions come from natural gas, natural seeps and the petroleum industry No (or negligible) ethane emissions from rice paddies, landfills, cows, water treatment plants If we can measure ethane and CH 4, we can estimate the emissions of CH 4 from the gas industry

5 Simpson et al. (2012), Nature, 488(7412), 490 4, doi: /nature Zeng et al. (2012), ACP, 12(16), , doi: /acp Global Ethane and Methane Measurements Atmospheric ethane declining globally In situ: Simpson et al Partial column remote sensing: Zeng et al Ethane decline linked to methane growth rate (Simpson et al. 2012)

6 Ethane Emissions in the South Coast Air Basin The MkIV Fourier transform spectrometer has measured ethane and CO in the south coast air basin since 1988 Up-looking retrievals from the ground Using the reported CARB CO emissions, ethane emissions can be calculated Blue squares are in situ measurements reported in Hsu et al. (2010) and Wennberg et al. (2012); red triangle is from new Caltech measurements

7 Production data source: Department of Conservation, Division of Oil, Gas, and Geothermal Resources, California Oil and Gas Production in the South Coast Air Basin It is not clear whether the long-term ethane emissions are related to either gas production or oil production in the basin a simultaneous methane measurement may be more definitive

8 Recent Studies of Methane and Ethane in the SCB Measured in situ during the ARCTAS 2008 and CALNEX 2010 aircraft campaigns Significant relationship between ethane and methane Reduction in C 2 H 6 /CH 4 slope 2008: 1.7±0.16% 2010: 1.5±0.11% SoCalGas pipeline C 2 H 6 /CH 4 slope: 2008: 2.09 ± 0.27% 2010: 1.65 ± 0.25% The drop of the C 2 H 6 /CH 4 slope in the atmosphere and in the natural gas suggests: some of the excess methane in the basin may be from delivered natural gas Wennberg et al. (2012), Environ. Sci. & Tech., doi: /es301138y.

9 New Total Column Measurements in the South Coast Air Basin Part of the Total Carbon Column Observing Network (TCCON) automated in June, 2012 Measure the column-averaged dry-air mole fraction Caltech instrument has an extra detector to measure further into the mid infrared (MIR) cm -1 This allows us to measure a suite of other gases: C 2 H 6, HCN, NO 2, NO, O 3 Isolated airmass: Bounded by mountains and the ocean Air sloshes around inside the basin

10 Diurnal Variability in XCO 2, XCO, XCH 4 and XC 2 H 6 in the South Coast Air Basin NIR MIR All species show similar diurnal patterns CO in the NIR is calibrated, not in the MIR, but we re interested in daily anomalies, not the absolute value (r 2 =0.97) Use CO to relate the MIR and NIR measurements

11 Methane and Ethane Correlations with CO Given CO emissions in the basin of 1.1±0.2 Tg/yr, we can calculate emissions: Wennberg et al. (2012) E CH m This work M M CH 4 = 4 CH 4 / CO CO E CO CH 4 /CO 55-76% 73±3% C 2 H 6 /CO % 1.4±0.1% C 2 H 6 /CH % 2.0±0.1% CH 4 Emissions Tg/yr 0.45±0.1 Tg/yr C 2 H 6 Emissions Gg/yr 16±3 Gg/yr

12 Ethane:Methane in the Natural Gas Pipelines The gas company samples its NG and records its composition ~monthly Playa Del Rey storage facility in the basin provides 3 years of data Not all pipelines contain the same gas ratios (grey boxes) Highlights the necessity for longer-term atmospheric measurements

13 Conclusions and Future Work Methane sources measured in the south coast air basin are times larger than CARB estimates Simultaneous measurements of C 2 H 6 and CH 4 help understand this discrepancy It should be possible to use these measurement techniques to monitor long term trends, seasonal changes We need longer-term estimates of the C 2 H 6 /CH 4 ratio for source attribution Combine this information with isotopic measurements (e.g. Townsend-Small et al. (2012)), and measurements of other species, such as propane to help bring the top-down and bottom-up estimates into agreement

14 Acknowledgments Eric Kort Nora Oshima OCO-2 Project LA Megacity Project Terrestrial Ecology Program NASA Upper Atmosphere Research program

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16 Total Carbon Column Observing Network (TCCON) TCCON instruments measure in the near infrared (NIR) CO 2, CH 4, CO, N 2 O, HF Solar absorption remote sensing measures sunlight from the coelostat - retrieve total columns of gases Main instrument is a high-resolution Fourier Transform spectrometer Measure the total column dry-air mole fraction

17 The Fourier Transform Spectrometer at Caltech Part of the Total Carbon Column Observing Network (TCCON) Caltech instrument is special because it has a third detector to measure further into the mid infrared (MIR) cm -1 This allows us to measure a suite of other gases: ethane, HCN, NO 2, NO, C 2 H 2, O 3 Caltech is located in the south coast air basin (SCB) Isolated airmass: Mountains on three sides Ocean on fourth side Air sloshes around inside the basin C 2 H 6 CO

18 Previous Methane Measurements from a TCCON Instrument at JPL The Oklahoma TCCON container was at JPL during Strong correlations measured in the diurnal changes in CH 4 relative to CO (and CO 2 ) If the emissions of one gas is known, the emissions of a correlated gas can be calculated Wunch et al. GRL, 2009

19 Comparing CO in the MIR and NIR A first comparison of CO in the two spectral regions shows that CO anomalies from the MIR don t match CO in the NIR After dividing the CO anomalies by the column averaging kernel values at the surface, the slope reduces from 2 to 1.1 Correlation coefficient remains high Averaging kernels are applied in this manner for all molecules from here on xˆ = x xˆ = a a + T xˆ x = T a a T x ( x x a )

20 Ethane Measurements from the Caltech TCCON FTS The instrument switches between detectors throughout the day There are good CO windows in the NIR and MIR region

21 Averaging Kernels The averaging kernel is the sensitivity of the measurement to absorption at various altitudes Since the emissions are at the surface, the sensitivity at the surface is most important The averaging kernel values at the surface differ significantly between weak (~NIR) and strong (~MIR) CO lines This must be taken into account, or the calculated emissions will be incorrect Weak CO Strong CO

22 Methane Emissions in Cities A few studies of CH 4 emissions in cities London: Lowry et al. (2001), JGR, doi: /2000jd Florence: Gioli et al. (2012), Environ. Pollution doi: /j.envpol Los Angeles: Wunch et al. (2009), GRL, doi: /2009gl Hsu et al. (2010), Atmos. Environ., doi: /j.atmosenv Wennberg et al. (2012), Environ. Sci. & Tech., doi: /es301138y. All claim that CH 4 emissions in cities are large and seek to find the sources Landfills Natural gas Petroleum industry Wetlands Ruminants

23 Wunch et al. (2009), GRL, 36(15), 1 5, doi: /2009gl Calculating Methane Emissions Use correlations between CH 4 and CO, and known emissions of CO from CARB to calculate emissions of CH 4 (or C 2 H 6, etc.) The CH 4 in the basin atmosphere is isotopically consistent with fossil fuels Townsend-Small et al. (2012) E CH m M M CH 4 = 4 CH 4 / CO CO E CO