  This paper considers the Free Differential Algebra and rheonomic
parametrization of type IIA Supergravity, extended to include the BRS
differential and the ghosts. We consider not only the ghosts lambda's of
supersymmetry but also the ghosts corresponding to gauge and Lorentz
transformations. In this way we can derive not only the BRS transformations of
fields and ghosts but also the standard pure spinor constraints on lambda's.
Moreover the formalism allows to derive the action for the pure spinor
formulation of type IIA superstrings in a general background, recovering the
action first obtained by Berkovits and Howe.
