  Warm absorber (WA) is an ionised gas present in the line of sight to the AGN
central engine. The effect of the absorber is imprinted in the absorption lines
observed in X-ray spectra of AGN. In this work, we model the WA in Seyfert 1
galaxy Mrk 509 using its recently published shape of broad band spectral energy
distribution (SED) as a continuum illuminating the absorber. Using the
photoionization code {\sc Titan}, recently we have shown that the absorption
measure distribution (AMD) found for this object can be successfully modelled
as a single slab of gas in total pressure (radiation+gas) equilibrium, contrary
to the usual models of constant density multiple slabs. We discuss the
transmitted spectrum that would be recorded by an observer after the radiation
from the nucleus passes through the WA.
