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Volume 16, issue 13
Atmos. Chem. Phys., 16, 8479-8498, 2016
https://doi.org/10.5194/acp-16-8479-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 8479-8498, 2016
https://doi.org/10.5194/acp-16-8479-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Jul 2016

Research article | 12 Jul 2016

Differential column measurements using compact solar-tracking spectrometers

Jia Chen1,a, Camille Viatte2, Jacob K. Hedelius2, Taylor Jones1, Jonathan E. Franklin1, Harrison Parker3, Elaine W. Gottlieb1, Paul O. Wennberg2, Manvendra K. Dubey3, and Steven C. Wofsy1 Jia Chen et al.
  • 1School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
  • 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
  • 3Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
  • anow at: Electrical and Computer Engineering, Technische Universität München, Munich, 80333, Germany

Abstract. We demonstrate the use of compact solar-tracking Fourier transform spectrometers (Bruker EM27/SUN) for differential measurements of the column-averaged dry-air mole fractions of CH4 and CO2 within urban areas. Using Allan variance analysis, we show that the differential column measurement has a precision of 0.01% for XCO2 and XCH4 with an optimum integration time of 10min, corresponding to Allan deviations of 0.04ppm and 0.2ppb, respectively. The sensor system is very stable over time and after relocation across the continent. We report tests of the differential column measurement, and its sensitivity to emission sources, by measuring the downwind-minus-upwind column difference ΔXCH4 across dairy farms in the Chino area, California, and using the data to verify emissions reported in the literature. Ratios of spatial column differences ΔXCH4∕ΔXCO2 were observed across Pasadena within the Los Angeles basin, indicating values consistent with regional emission ratios from the literature. Our precise, rapid measurements allow us to determine significant short-term variations (5–10min) of XCO2 and XCH4 and to show that they represent atmospheric phenomena.

Overall, this study helps establish a range of new applications for compact solar-viewing Fourier transform spectrometers. By accurately measuring the small differences in integrated column amounts across local and regional sources, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale. The inference of the source strength is much more direct than inversion modeling using only surface concentrations and less subject to errors associated with small-scale transport phenomena.

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This paper helps establish a range of new applications for compact solar-tracking Fourier transform spectrometers, and shows the capability of differential column measurements for determining urban emissions. By accurately measuring the differences in the integrated column amounts of carbon dioxide and methane across local and regional sources in California, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale.
This paper helps establish a range of new applications for compact solar-tracking Fourier...
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