VOCs and NO_x dependency of simulated OPEs. VOCs and NO_x dependence of instantaneous OPEs calculated from the box model and GEOS-Chem. Data points are color-coded by OPE values and each row indicates total Korea, urban, and rural areas. Dashed lines indicate three different VOC to NO_x ratios (VOC/NO_x), 40, 10, 2.5, from bottom to top. DOI: https://doi.org/10.1525/elementa.394.f7