Ambient ground-level ozone (O3) and fine particulate matter (PM2.5) contribute to adverse health impacts. Among controllable emission precursors, anthropogenic nitrogen oxides (NOx = NO + NO2) and volatile chemical products (VCP) are contributors to O3 and PM2.5 formation across the continental United States. Accurately assessing the relative contributions of pollution precursors to pollutant formation is crucial for prioritizing emission reduction strategies. Because of the complex formation pathways, the relationship between pollutants and emissions can be highly nonlinear. Traditional finite-difference approaches often fail to fully capture these nonlinearities. In this work, we leverage CMAQ-hyd, an augmented version of the Community Multiscale Air Quality Model (CMAQ v5.3.2), to perform higher-order sensitivity analysis and quantify both linear and nonlinear impacts of NOx and VCP on O3 and PM2.5 formation. Results reveal the impact on acute premature mortality of reducing these precursor emissions. In densely populated cities, a domain-wide reduction in NOx emissions could produce significantly more population-weighted O3 exposure and associated acute health disbenefits. The reduction of VCP emissions generally leads to reduction in both pollutants, suggesting more opportunities for strategic management especially in densely populated cities. By providing sensitivities, CMAQ-hyd offers a robust framework for evaluating pollutant formation pathways and assessing the health implications of various emission scenarios.
Liu et al. (Wed,) studied this question.