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

摘要

The high-order decoupled direct method in three dimensions for particulatematter (HDDM-3D/PM) has been implemented in the Community Multiscale AirQuality (CMAQ) model to enable advanced sensitivity analysis. The majoreffort of this work is to develop high-order DDM sensitivity analysis ofISORROPIA, the inorganic aerosol module of CMAQ. A case-specific approachhas been applied, and the sensitivities of activity coefficients and watercontent are explicitly computed. Stand-alone tests are performed forISORROPIA by comparing the sensitivities (first- and second-order) computedby HDDM and the brute force (BF) approximations. Similar comparison has alsobeen carried out for CMAQ sensitivities simulated using a week-long winterepisode for a continental US domain. Second-order sensitivities of aerosolspecies (e.g., sulfate, nitrate, and ammonium) with respect to domain-wideSO₂, NO_x, and NH₃ emissions show agreement with BF results,yet exhibit less noise in locations where BF results are demonstrablyinaccurate. Second-order sensitivity analysis elucidates poorly understoodnonlinear responses of secondary inorganic aerosols to their precursors andcompeting species. Adding second-order sensitivity terms to the Taylorseries projection of the nitrate concentrations with a 50% reduction indomain-wide NO_x or SO₂ emissions rates improves the predictionwith statistical significance.