Atmos. Chem. Phys. Discuss., 13, 21203-21257, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Retrieving tropospheric nitrogen dioxide over China from the Ozone Monitoring Instrument: effects of aerosols, surface reflectance anisotropy and vertical profile of nitrogen dioxide
J.-T. Lin1, R. V. Martin2,3, K. F. Boersma4,5, M. Sneep4, P. Stammes4, R. Spurr6, P. Wang7, M. Van Roozendael8, K. Clémer9, and H. Irie10
1Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
2Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
3Atomic and Molecular Physics Division, Harvard, Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
4Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
5Fluid Dynamics Lab, Eindhoven University of Technology, Eindhoven, the Netherlands
6RT Solutions Inc., Cambridge MA 02138, USA
7IAP/CAS, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
8BIRA-IASB, Belgian Institute for Space Aeronomy, Brussels, Belgium
9Instituut voor sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium
10Center for Environmental Remote Sensing, Chiba University, 1-33 Yayoicho, Inage-ku, Chiba 263-8522, Japan

Abstract. Retrievals of tropospheric nitrogen dioxide (NO2) from the Ozone Monitoring Instrument (OMI) are subject to errors in the treatments of aerosols, surface reflectance anisotropy, and vertical profile of NO2. Here we quantify the influences over China via an improved retrieval process. We explicitly account for aerosol optical effects (simulated by nested GEOS-Chem at 0.667° lon × 0.5° lat and constrained by aerosol measurements), surface reflectance anisotropy, and high-resolution vertical profiles of NO2 (simulated by GEOS-Chem). Prior to the NO2 retrieval, we derive the cloud information using consistent ancillary assumptions. We compare our retrieval to the widely used DOMINO v2 product, using as reference MAX-DOAS measurements at three urban/suburban sites in East China and focusing the analysis on the 127 OMI pixels (in 30 days) closest to the MAX-DOAS sites. We find that our retrieval reduces the interference of aerosols on the retrieved cloud properties, thus enhancing the number of valid OMI pixels by about 25%. Compared to DOMINO v2, our retrieval improves the correlation with the MAX-DOAS data in the day-to-day variability of NO2 (R2 = 0.96 vs. 0.72). Our retrieved NO2 columns are about 50% of the MAX-DOAS data on average. This reflects the inevitable spatial inconsistency between the two types of measurement, uncertainties in MAX-DOAS data, and residual uncertainties in our OMI retrievals related to aerosols and vertical profile of NO2. Through a series of tests, we find that excluding aerosol scattering/absorption can either increase or decrease the retrieved NO2, with a mean absolute difference by about 20%. Concentrating aerosols at the boundary layer top enhances the retrieved NO2 by 8% on average with a mean absolute difference by 23%. The aerosol perturbations also affect nonlinearly the retrieved cloud fraction and particularly cloud pressure. Employing various surface albedo datasets alters the retrieved NO2 by 0–7% on average. The retrieved NO2 columns increase when the NO2 profiles are taken from MAX-DOAS retrievals (by 20% on average) or TM4 simulations (by 10%) instead of GEOS-Chem simulations. Our findings are also relevant to retrievals of other pollutants (e.g., sulfur dioxide, formaldehyde, glyoxal) from UV-vis backscatter satellite instruments.

Citation: Lin, J.-T., Martin, R. V., Boersma, K. F., Sneep, M., Stammes, P., Spurr, R., Wang, P., Van Roozendael, M., Clémer, K., and Irie, H.: Retrieving tropospheric nitrogen dioxide over China from the Ozone Monitoring Instrument: effects of aerosols, surface reflectance anisotropy and vertical profile of nitrogen dioxide, Atmos. Chem. Phys. Discuss., 13, 21203-21257, doi:10.5194/acpd-13-21203-2013, 2013.
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