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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 12 Nov 2019

Submitted as: research article | 12 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Inverse modeling of SO2 and NOx emissions over China using multi-sensor satellite data: 1. formulation and sensitivity analysis

Yi Wang1, Jun Wang1,2, Xiaoguang Xu2,3, Daven K. Henze4, and Zhen Qu4 Yi Wang et al.
  • 1Interdisciplinary Graduate Program in Informatics, The University of Iowa, Iowa City, IA 52242, USA
  • 2Department of Chemical and Biochemical Engineering, and Center for Global & Regional Environmental Research, The University of Iowa, Iowa City, IA 52242, USA
  • 3Joint Center for Earth Systems Technology and Department of Physics, University of Maryland Baltimore County, Baltimore, Maryland, 21250, USA
  • 4Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA

Abstract. SO2 and NO2 observations from the Ozone Mapping and Profiler Suite (OMPS) sensor are used for the first time in conjunction with GEOS-Chem adjoint model to optimize both SO2 and NOx emission estimates over China for October 2013. OMPS SO2 and NO2 observations are first assimilated separately to optimize emissions of SO2 and NOx, respectively. Posterior emissions, compared to the prior, yield improvements in simulating columnar SO2 and NO2, in comparison to measurements from OMI and OMPS. The posterior SO2 and NOx emissions from separate inversions are 748 Gg S and 672 Gg N, which are 36 % and 6 % smaller than prior MIX emissions, respectively. In spite of the large reduction of SO2 emissions over the North China Plain, the simulated sulfate-nitrate-ammonium Aerosol Optical Depth (AOD) only decrease slightly, which can be attributed to (a) nitrate rather than sulfate as the dominant contributor to AOD and (b) replacement of ammonium sulfate with ammonium nitrate as SO2 emissions are reduced. Both data quality control and the weight given to SO2 relative to NO2 observations can affect the spatial distributions of the joint inversion results. When the latter is properly balanced, the posterior emissions from assimilating OMPS SO2 and NO2 jointly yield a difference of −3 % to 15 % with respect to the separate assimilations for total anthropogenic SO2 emissions and ± 2 % for total anthropogenic NOx emissions; but the differences can be up to 100 % for SO2 and 40 % for NO2 in some grid cells. Improvements on SO2 and NO2 simulations evaluated with OMPS and OMI measurements from the joint inversions are overall consistent with those from separate inversions. Moreover, the joint assimilations save ~ 50 % of the computational time than assimilating SO2 and NO2 separately when computational resources are limited to run one inversion at a time sequentially. The sensitivity analysis shows that a perturbation of NH3 to 50 % (20 %) of the prior emission inventory: (a) has negligible impact on the separate SO2 inversion, but can lead to decrease of posterior SO2 emissions over China by −2.4 % (−7.0 %) in total and up to −9.0 % (−27.7 %) in some grid cells in the joint inversion with NO2; (b) yield posterior NOx emissions over China decrease by −0.7 % (−2.8 %) for the separate NO2 inversion and by −2.7 % (−5.3 %) in total and up to −15.2 % (−29.4 %) in some grid cells for the joint inversion. The large reduction of SO2 between 2010 and 2013, however, only leads to ~ 10 % decrease of aerosol optical depth regionally; reducing surface aerosol concentration requires the reduction of emissions of NH3 as well.

Yi Wang et al.
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Short summary
Formulation f using OMPS satellite observation to inverse SO2 and NO2 emissions is presented through GEOS-Chem adjoint modeling framework. The work is illustrated over China region. The robustness of the results is studied through separate and joint inversions of SO2 and NO2 and consideration of NH3 uncertainty. Independent validation is performed with OMI SO2 and NO2 data. It shown that simultaneous inversion of NO2 and SO2 from OMPS provides an effective way to rapidly update emissions.
Formulation f using OMPS satellite observation to inverse SO2 and NO2 emissions is presented...