Fig. 4. The schematic distributions of and near the ionization front, i.e. the ionization structure of the surface layer of the cloud in BLR.
![[FIGURE]](img375.gif)
![[FORMULA]](img369.gif)
and ![[FORMULA]](img371.gif)
near the ![[FORMULA]](img373.gif)
ionization front, i.e. the ionization structure of the surface layer of the cloud in BLR.