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Accounting for aerosol scattering in the CLARS retrieval of column averaged CO_2 mixing ratios

Zhang, Qiong and Natraj, Vijay and Li, King-Fai and Shia, Run-Lie and Fu, Dejian and Pongetti, Thomas J. and Sander, Stanley P. and Roehl, Coleen M. and Yung, Yuk L. (2015) Accounting for aerosol scattering in the CLARS retrieval of column averaged CO_2 mixing ratios. Journal of Geophysical Research. Atmospheres, 120 (14). pp. 7205-7218. ISSN 2169-897X. doi:10.1002/2015JD023499.

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The California Laboratory for Atmospheric Remote Sensing Fourier transform spectrometer (CLARS‐FTS) deployed at Mount Wilson, California, has been measuring column abundances of greenhouse gases in the Los Angeles (LA) basin in the near‐infrared spectral region since August 2011. CLARS‐FTS measures reflected sunlight and has high sensitivity to absorption and scattering in the boundary layer. In this study, we estimate the retrieval biases caused by aerosol scattering and present a fast and accurate approach to correct for the bias in the CLARS column averaged CO2 mixing ratio product, X_(CO2). The high spectral resolution of 0.06 cm^(−1) is exploited to reveal the physical mechanism for the bias. We employ a numerical radiative transfer model to simulate the impact of neglecting aerosol scattering on the CO_2 and O_2 slant column densities operationally retrieved from CLARS‐FTS measurements. These simulations show that the CLARS‐FTS operational retrieval algorithm likely underestimates CO_2 and O_2 abundances over the LA basin in scenes with moderate aerosol loading. The bias in the CO_2 and O_2 abundances due to neglecting aerosol scattering cannot be canceled by ratioing each other in the derivation of the operational product of X_(CO2). We propose a new method for approximately correcting the aerosol‐induced bias. Results for CLARS X_(CO2) are compared to direct‐Sun X_(CO2) retrievals from a nearby Total Carbon Column Observing Network (TCCON) station. The bias‐correction approach significantly improves the correlation between the X_(CO2) retrieved from CLARS and TCCON, demonstrating that this approach can increase the yield of useful data from CLARS‐FTS in the presence of moderate aerosol loading.

Item Type:Article
Related URLs:
URLURL TypeDescription
Zhang, Qiong0000-0002-8762-0557
Natraj, Vijay0000-0003-3154-9429
Li, King-Fai0000-0003-0150-2910
Shia, Run-Lie0000-0003-1911-3120
Pongetti, Thomas J.0000-0001-9465-0853
Sander, Stanley P.0000-0003-1424-3620
Roehl, Coleen M.0000-0001-5383-8462
Yung, Yuk L.0000-0002-4263-2562
Alternate Title:Influence of Aerosol Scattering on the Retrieval of CO_2 Mixing Ratios: A Case Study Using Measurements from the California Laboratory for Atmospheric Remote Sensing (CLARS)
Additional Information:© 2015 American Geophysical Union. Received 13 APR 2015; Accepted 2 JUL 2015; Accepted article online 3 JUL 2015; Published online 29 JUL 2015. We thank Paul Wennberg, C. Wong, J. Margolis, S. Newman, C. Miller, D. Crisp, M. Gerstell, X. Xi, P. Kopparla, P. Gao, R. Hu, and L. Kuai for their helpful comments. We thank Jochen Stutz and his staff for establishing and maintaining the AERONET Caltech site used in this investigation. We also thank the anonymous reviewers whose comments helped improve the manuscript significantly. This research was supported in part by NASA grant NNX13AK34G to the California Institute of Technology, grant P1367828 from the Jet Propulsion Laboratory, and the KISS program at Caltech. Support for CLARS from the California Air Resources Board, NOAA Climate Program, NIST GHG and Climate Science Program, NASA Carbon Cycle Science Program, and JPL Earth Science and Technology Directorate is gratefully acknowledged. TCCON data were obtained from the TCCON Data Archive, hosted by the Carbon Dioxide Information Analysis Center— AERONET data for this paper can be downloaded online. CLARS‐FTS data are available from the authors upon request.
Group:Keck Institute for Space Studies
Funding AgencyGrant Number
Keck Institute for Space Studies (KISS)UNSPECIFIED
Subject Keywords:aerosol; scattering; X_(CO2)
Issue or Number:14
Record Number:CaltechAUTHORS:20140822-092514611
Persistent URL:
Official Citation:Zhang, Q., V. Natraj, K.‐F. Li, R.‐L. Shia, D. Fu, T. J. Pongetti, S. P. Sander, C. M. Roehl, and Y. L. Yung (2015), Accounting for aerosol scattering in the CLARS retrieval of column averaged CO2 mixing ratios. J. Geophys. Res. Atmos., 120, 7205–7218. doi: 10.1002/2015JD023499
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48801
Deposited By: Tony Diaz
Deposited On:25 Aug 2014 04:35
Last Modified:10 Nov 2021 18:36

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