Sensitivity of Ozone Production to NO_x and VOC Along the Lake Michigan Coastline

We report on the sensitivity of enhanced ozone (O₃) production, observed during lake breeze circulation along the coastline of Lake Michigan, to the concentrations of nitrogen oxides (NO_x = NO + NO₂) and volatile organic compounds (VOCs). We assess the sensitivity of O₃ production to NO_x and VOC on a high O₃ day during the Lake Michigan Ozone Study 2017 using an observationally constrained chemical box model that implements the Master Chemical Mechanism (MCM v3.3.1) and recent emission inventories for NO_x and VOCs. The Master Chemical Mechanism model is coupled to a backward air mass trajectory analysis from a ground supersite in Zion, IL, where an extensive series of measurements of O₃ precursors and their oxidation products, including hydrogen peroxide (H₂O₂), nitric acid (HNO₃), and particulate nitrates (NO₃ ⁻) serve as model constraints. We evaluate the chemical evolution of the Chicago-Gary urban plume as it advects over Lake Michigan and demonstrate how modeled indicators of VOC- versus NO_x-sensitive regimes can be constrained by measurements at the trajectory endpoint. Using the modeled ratio of the instantaneous H₂O₂ and HNO₃ production rates (P_H2O2/P_HNO3), we suggest that O₃ production over the urban source region is strongly VOC sensitive and progresses towards a more NO_x-sensitive regime as the plume advects north along the Lake Michigan coastline on this day. We also demonstrate that ground-based measurements of the mean concentration ratio of H₂O₂ to HNO₃ describe the sensitivity of O₃ production to VOC and NO_x as the integral of chemical production along the plume path.