Until further notice, the Wednesday CTP colloquia will be starting at 12:30 PM. Seminar will be given via Zoom: Link: https://us02web.zoom.us/j/233346745?pwd=aEtnb2pvdlZOdnYycm5XczVxb3EwUT09 Ask anyone from CTP PAS about password!! Abstract Central parts of Active Galactic Nuclei are spatially unresolved but studying their radiation spectra and time variability astronomers try to recreate 3-D picture. In my talk I will mostly concentrate on the region located at a distance of hundreds or thousands of gravitational radii where broad emission lines are produced. These broad emission lines are the most characteristic features of the radiation spectra of active galaxies, and those features (Balmer lines) allowed in 60' to deduce the nature of quasars as extremely bright galactic nuclei at cosmological distances. Still the problem of the origin of the material forming these lines is not uniquely solved. We develop a model in which the matter comes from the accretion disk, lifted up by the radiation pressure acting on dust. We calculate the motion of dusty clouds and confront the model with the observational constraints coming from the time delay of the line emission with respect to the continuum.