In this paper, some additive properties of the pseudo Drazin inverse are
obtained in a Banach algebra. In addition, we find some new conditions under
which the pseudo Drazin inverse of the sum a + b can be explicitly expressed
in terms of a, az, b, bz. In particular, necessary and sufficient conditions
for the existence as well as the expression for the pseudo Drazin inverse of
the sum a+b are obtained under certain conditions. Also, a result of Wang
and Chen [Pseudo Drazin inverses in associative rings and Banach algebras,
LAA 437(2012) 1332-1345] is extended.