Figure S4 . Total Column ozone (DU) on March 18th 2020 (a) observed by OMI, (b) from model run CNTL and (c) from model run WA. The 220 DU contour is indicated by the white line. Panel (d) shows the difference in column ozone (DU) between runs WA and CNTL. The -100 DU contour is indicated by the dotted white line. Panels (a) and (b) show the same data as Figure 3 in the main paper but on a different colour scale to accommodate results from run WA.