Location-Specific Control of Precursor Emissions to Mitigate Photochemical Air Pollution

An adjoint-based air quality modelingstudy that evaluatesregional air quality benefits of targeted location-specific NO x control in California's San JoaquinValley and delineates how high-priority locations change by year andby choice of regional versus city-level receptors. The effects of precursor emission controls on air qualitycan varygreatly depending on where emission reductions occur. We use the adjointof the Community Multiscale Air Quality (CMAQ) model to evaluate impactsof spatially targeted NO x emission reductionson odd oxygen (O- x = O-3 + NO2). The air quality responses studied here include one population-weightedregionwide and three city-level receptors in Central California. Wemap high-priority locations for NO x controland their changes over decadal time scales. The desirability of NO x -focused emission control programs has increasedbetween 2000 and 2022. We find for present-day conditions that reducingNO( x ) emissions by 28% from targeted high-prioritylocations can achieve 60% of the air quality benefits of uniform NO x reductions at all locations. High-prioritysource locations are found to differ for individual city-level versusregionwide receptors of interest. While high-impact emission hotspotsfor improving city-level metrics are found within the city itselfor closely adjacent, the spatial pattern of emission hotspots forimproving regionwide air quality is more complex and requires comprehensiveconsideration of upwind sources. Results of this study can help toinform strategic decision-making at local and regional levels aboutwhere to prioritize emission control efforts.