Fig. 4: Hourly variations of ground-observed and predicted PM2.5 in Seoul.

Panels a–f present comparisons between observed PM2.5 and predicted PM2.5 obtained in the experiments a from CAMS NRT, b from the control run (without 3DV), c with 3DV using MODIS AOD, d with 3DV using GOCI AOD, e with 3DV using ground observations, and f with 3DV using both GOCI AOD and ground observations. The three gray-shaded areas represent Asian dust (I), air stagnant (II), and long-range transport (III) episodes, respectively.