Decoupled direct 3D sensitivity analysis for particulate matter (DDM-3D/PM)

Abstract

The decoupled direct method (DDM) and DDM-3D have been implemented in air quality models in order to efficiently compute sensitivities. Initial implementation of DDM/DDM-3D in models was confined only to gas-phase species as the treatment of sensitivities in the dynamics of secondary aerosol formation is more complex. Here, it is extended to calculate particulate matter sensitivities. DDM-3D/particulate matter (PM) results compare well spatially and temporally with the traditional brute-force approach, particularly for species responses to emissions of their “parent” precursor (e.g., sulfate to SO 2 emissions.) Correlations of more indirect relationships between aerosols and gaseous emissions (e.g., nitrate to SO 2 emissions) are worse, but these sensitivities are usually small. DDM-3D/PM appears to work better than the brute-force approach in some cases due to numerical noise and other factors, as identified from the application on a southeastern US domain for a summer episode. DDM-3D/PM is also computationally efficient. While CPU usage was found to scale linearly with the number of sensitivity parameters of interest (for a given domain size), it was significantly less than using the brute-force approach.