Search

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 NOxand 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/LNOxand formaldehyde to NO2ratio (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. 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 NOxand 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 NOxemissions, 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 days over Lake Michigan, a 10% decrease in VOC (NOx) emissions can lower ozone in the key high ozone zone over southern Lake Michigan by 0.4% (0.8%). Volatile chemical products, an uncertain component of emission inventories, are responsible for 2.7 ppb (∼4%) of ozone. Outside of a small (85 km) zone downwind of Chicago, ozone concentrations and production near Lake Michigan is generally NOx‐sensitiveOn event days 10% decrease in volatile organic compound emission can lower MDA8 by 0.4% and 10% decrease in nitrogen oxides emission can lower MDA8 by 0.8% over Lake MichiganVolatile chemical product emissions were modeled to produce an average 2.7 ppb ozone increase over the lake Outside of a small (85 km) zone downwind of Chicago, ozone concentrations and production near Lake Michigan is generally NOx‐sensitive On event days 10% decrease in volatile organic compound emission can lower MDA8 by 0.4% and 10% decrease in nitrogen oxides emission can lower MDA8 by 0.8% over Lake Michigan Volatile chemical product emissions were modeled to produce an average 2.7 ppb ozone increase over the lake