Adjoint Sensitivity Analysis to Determine Potential and Existing Precursor Contributions to Ozone Burdens Under Different Synoptic Events

Abstract:

California’s San Joaquin Valley is one of the top two ozone nonattainment areas in the U.S. due to its unique geography as well as diverse emission sources from both local and upwind areas. More than half of the California’s disadvantaged communities are located in this region and the valley’s population is rapidly growing. To effectively and efficiently mitigate ozone air pollution problems for both protecting the disadvantaged communities and meeting the ozone standard, it is important to understand the ozone precursor contributions resolved in time and space for both existing sources and potential new sources in anticipation of the region’s rapid growth.

This study aims determine the ozone precursor contributions to two impact metrics: ozone burdens in SJV disadvantaged communities and ozone burdens in the non-attainment areas. As varying mesoscale flows under different synoptic events directly influence spatial distributions of ozone and the source-receptor relationships, the simulations are conducted under three representative synoptic events determined from cluster analysis over a summer season. We use an adjoint tool coupled to EPA’s chemical transport model (CMAQ). The adjoint tool enables efficient calculation of ozone sensitivities to large numbers of model parameters such that influential precursor emissions can be resolved at high spatial and temporal resolution for both existing and potential source locations. We will delineate areas of influence in space and time and determine variabilities in ozone sensitivities to limiting reagents for the aforementioned two impact metrics across different flow and temperature regimes. Our results will enhance the understanding of the underlying physicochemical processes that connect ozone air pollution for both protection of public health and compliance of ozone standards.