The Decoupled Direct Method for Higher-Order Sensitivity Analysis for Particulate Matter in Multidimensional Air Quality Models

The decoupled direct method (DDM) has been implemented in air quality models to effectively perform second-order sensitivity analysis of particulate matter (PM). The application of DDM sensitivity analysis is currently available in the Community Multiscale Air Quality (CMAQ) model for first- and second-order sensitivities of gas-phase species as well as first-order sensitivities of PM. As gas-phase species and particulate matter are closely coupled; and as the higher-order sensitivities can better capture the non-linear responses, in this work, DDM sensitivity analysis is extended to compute second-order PM sensitivities. Also, particulate matter often exists as non-ideal solutions, so the effect of chemical activity on the DDM sensitivity analysis of PM is evaluated. An initial application is to assess the non-linearity in the response of PM to SO2, NOx, and ammonia emission controls.