Computation of Numerically Exact First- and Second-Order Sensitivities of Biogenic Aerosols Formation Using a Column Model Version of CMAQ-hyd

JIACHEN LIU, Eric Chen, Ryan Russell, Shannon Capps, Drexel University

     Abstract Number: 331
     Working Group: Source Apportionment

Abstract
Secondary organic aerosols (SOA) are generated by complex transformations of organic molecule emissions and are a significant contributing factor to atmospheric particulate matter (PM) concentrations. High PM concentrations can lead to regional haze and pose health risks to the public. The formation of SOAs from biogenic precursors including monoterpenes remains poorly understood, and biogenic SOAs have become a major source of total SOA concentrations, especially in the southeastern U.S. Therefore, understanding the sensitivities of biogenic precursors with respect to SOA formation is essential for guiding scientists and policymakers to understand the background biogenic SOA concentrations. Previous methods of calculating the sensitivity coefficients include the finite difference method (FDM), the direct decoupled method (DDM), and the adjoint method. The finite difference method suffers from truncation and cancellation errors, while the DDM and the adjoint method are relatively hard to implement and update in chemical transport models. Here, we propose an alternate approach to calculate first- and second-order sensitivities. This method is an operator overloading approach that can calculate the exact sensitivity coefficients through one single run of the model. We applied this method in the Community Multiscale Air Quality (CMAQ) model v.5.3 with the cb6r3-aero7 mechanism to formulate the CMAQ-hyd model. In this work, we apply a column model version of the CMAQ-hyd to compute the exact sensitivities of SOA concentrations with respect to their precursor concentrations. This type of sensitivity analysis could guide policymakers in evaluating the current Regional Haze Rule and potentially revisions of the National Ambient Air Quality Standard for the total atmospheric PM_2.5 concentration in the future.