Sensitivity of Ozone Production to NO x and VOC Along the Lake Michigan Coastline

We report on the sensitivity of enhanced ozone (O 3 ) production, observed during lake breeze circulation along the coastline of Lake Michigan, to the concentrations of nitrogen oxides (NO x = NO + NO 2 ) and volatile organic compounds (VOCs). We assess the sensitivity of O 3 production to NO x and VOC on a high O 3 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 O 3 precursors and their oxidation products, including hydrogen peroxide (H 2 O 2 ), nitric acid (HNO 3 ), and particulate nitrates (NO 3 − ) 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 H 2 O 2 and HNO 3 production rates ( P H2O2 / P HNO3 ), we suggest that O 3 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 H 2 O 2 to HNO 3 describe the sensitivity of O 3 production to VOC and NO x as the integral of chemical production along the plume path. Direct observations of H 2 O 2 /HNO 3 at an urban plume endpoint can be used to assess the integrated O 3 sensitivity to NO x and VOC emissions Indicators of O 3 sensitivity show that the urban plume traveling over Lake Michigan evolves from VOC towards NO x ‐sensitive O 3 production O 3 , H 2 O 2 , HNO 3 , and NO 3 − provide unique constraints to predict the response of O 3 to changes in VOC and NO x emissions in coastal regions