Advancing EKMA Applications in Regional Air Quality Models: Insights into Interpretive Biases and Ozone Abatement Policies

The Empirical Kinetics Modeling Approach (EKMA) is a valuable tool for guiding ozone (O 3 ) precursor emission controls, but O 3 isopleths generated through regional emission perturbations in regional air quality models (RAQMs) may hide interpretive biases for local applications. Using the WRF-CMAQ model, this study constructs city-specific EKMA diagrams by perturbing O 3 precursor emissions across the Greater Bay Area (GBA) of China and integrates source apportionment to quantify these biases. Results reveal that such isopleths overestimate city-specific control efficacy by approximately 58.7% on average across the GBA cities, based on monthly O 3 metrics, with biases persisting as high as 47.2% even in relatively stagnant meteorological conditions. This indicates that local isopleths derived from regional emission perturbations inadequately represent the effectiveness of local emission controls. Reinterpreting the city-specific isopleths from a regional emission reduction perspective and applying multiple air quality indicators, we observe O 3 concentration rebounds in numerous GBA cities due to inappropriate NO x reductions. Nonetheless, when shifting to a risk-based perspective, short-term NO x reductions achieve overall health benefits by offsetting greater NO 2 risks, which outweigh the elevated O 3 -related risks in VOC-limited regimes. These insights provide evidence supporting governmental efforts to prioritize short-term, cost-effective NO x -focused controls, which deliver immediate health benefits, particularly in high-NO x urban cores. Additionally, this study offers positive incentives for adopting long-term attainment strategies with balanced NO x:AVOCs (anthropogenic VOCs) ratios of 1:1 or even 2:1 to achieve air pollution abatement and decarbonization in the GBA simultaneously. Our work highlights the imperative of aligning EKMA-RAQMs diagram interpretations with experimental designs and provides a novel perspective for holistically evaluating regional emission control policies.