Articles | Volume 5, issue 2
Geosci. Model Dev., 5, 355–368, 2012
https://doi.org/10.5194/gmd-5-355-2012
Geosci. Model Dev., 5, 355–368, 2012
https://doi.org/10.5194/gmd-5-355-2012

Development and technical paper 23 Mar 2012

Development and technical paper | 23 Mar 2012

Development of the high-order decoupled direct method in three dimensions for particulate matter: enabling advanced sensitivity analysis in air quality models

W. Zhang1, S. L. Capps2, Y. Hu3, A. Nenes1,2, S. L. Napelenok4, and A. G. Russell3 W. Zhang et al.
  • 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 2School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 3School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 4US Environment Protection Agency, Research Triangle Park, North Carolina, USA

Abstract. The high-order decoupled direct method in three dimensions for particulate matter (HDDM-3D/PM) has been implemented in the Community Multiscale Air Quality (CMAQ) model to enable advanced sensitivity analysis. The major effort of this work is to develop high-order DDM sensitivity analysis of ISORROPIA, the inorganic aerosol module of CMAQ. A case-specific approach has been applied, and the sensitivities of activity coefficients and water content are explicitly computed. Stand-alone tests are performed for ISORROPIA by comparing the sensitivities (first- and second-order) computed by HDDM and the brute force (BF) approximations. Similar comparison has also been carried out for CMAQ sensitivities simulated using a week-long winter episode for a continental US domain. Second-order sensitivities of aerosol species (e.g., sulfate, nitrate, and ammonium) with respect to domain-wide SO2, NOx, and NH3 emissions show agreement with BF results, yet exhibit less noise in locations where BF results are demonstrably inaccurate. Second-order sensitivity analysis elucidates poorly understood nonlinear responses of secondary inorganic aerosols to their precursors and competing species. Adding second-order sensitivity terms to the Taylor series projection of the nitrate concentrations with a 50% reduction in domain-wide NOx or SO2 emissions rates improves the prediction with statistical significance.

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