Potential effects of climate and emissions changes on surface ozone in the Chicago area

Future changes in climate and precursor emissions will likely have important consequences on ground-level ozone concentrations for the City of Chicago and its surrounding suburban/rural areas. Here we use a regional climate-air quality modeling system to evaluate the combined and individual effects of climate warming (and resulting biogenic emissions increases) and anthropogenic emissions perturbations from 1996-2000 to 2048-2052 and 2095-2099 in this region. Two scenarios are considered, including A1FI (higher warming with increasing anthropogenic emissions) and B1 (less warming with reduced anthropogenic emissions). Relative to 1996-2000, projected changes in climate and anthropogenic emissions together lead to little ozone change for the City of Chicago under A1FI but 5.0-7.8 ppb increases under B1 by 2048-2052 and 2095-2099. For A1FI, the decreasing ratio of volatile organic compounds (VOCs) to nitrogen oxides (NOx) reduces ozone concentrations over Chicago, despite the increasing emissions for both NOx and VOCs. Averaged over the Chicago urban and surrounding suburban area, however, surface ozone increase 2.3-7.1 ppb under A1FI by 2095-2099. Additionally, the seasonal ozone variation is projected to increase 84-127% under A1FI but decrease 23-30% under B1 over the Chicago area. By comparison, projected climate warming alone increases the surface ozone by 2.1-8.7 ppb and its seasonal variation by 22-89% over the Chicago area from 1996-2000 to 2095-2099 under both scenarios. Therefore, effective emission regulation and climate considerations are both important to pollution mitigation in the Chicago area.