The Impact of Volatile Chemical Products, Other VOCs, and NOx on Peak Ozone in the Lake Michigan Region

High concentrations of ozone along the coastline of Lake Michigan are a persistent air quality management challenge. Complementing observations during the 2017 Lake Michigan Ozone Study (LMOS 2017), WRF‐Chem modeling was used to quantify sensitivity of modeled ozone (O3) to anthropogenic nitrogen oxides (NOx) and volatile organic compound (VOC) emissions, including to changes in volatile chemical product (VCP). The daily maximum 8 hr average (MDA8) over the high ozone region of Lake Michigan decreased by 2.7 ppb with exclusion of VCP from the inventory, and was sensitive to both NOx and VOC changes, with greater sensitivity to NOx. Close to urban centers, MDA8 ozone was VOC‐sensitive. Clusters of coastal receptor sites were identified based on similarity in response to emission perturbations, with most clusters being NOx‐sensitive and NOx‐sensitivity increasing with distance from major emission sources. The 2 June 2017 ozone event, which has received considerable focus, is shown to be atypical due to unusually strong and spatially extended VOC‐sensitive behavior. WRF‐Chem integrated reaction rate analysis was used to compute radical termination rates due to NOx (LNOx) and to radical‐radical reactions (LROx). LROx/LNOx and formaldehyde to NO2 ratio (FNR) were shown to be predictive of modeled MDA8 ozone sensitivity, but with variation in predictive power as a function of time of day, which has implications for air quality management use of FNR from geostationary satellites. Plain Language Summary Surface ozone is an air pollutant of concern due to human health impacts. In locations with elevated ozone concentrations, including coastal regions around Lake Michigan, ozone pollution is managed by controlling emissions of the two classes of chemicals that drive ozone chemistry: volatile organic compounds (VOCs) and nitrogen oxides (NOx). However, due to large reductions in emissions of NOx and VOC over the past 20 years, the leverage that future reductions will have is uncertain. Reductions of 4–5 ppb (∼7%) are needed in several locations, relative to 2017–2019 concentrations, to meet the 2015 ozone standard of 70 ppb. In this paper, we use simulations of atmospheric chemistry and airflow over the Midwestern US to address this issue. By comparing simulations based on different VOC and NOx emissions, we find that reductions in NOx emissions have more influence on ozone than reductions in VOC emissions, except for a small zone downwind of Chicago. On high ozone d