Аннотация:Gas in the shadow of clouds in the outer parts of the broad line region can radiate a considerable fraction (dozens of percent) of the narrow emission line flux. The variability of the X-ray luminosity of the central source should result in significant variations of the gas emission on a timescale of months. Particularly strong changes of line intensities and column densities of gas in the shadow (\equiv10$^23$cm$^-2$) can be produced by phase transfer between two thermally stable fluids with temperatures 10 - 20\times10$^3$K and 40 - 100\times10$^3$K, which can exist in the shadow of clouds.