New Volume Comparison Results and Volume Growth Rigidity of Gradient Ricci Almost Solitons

In this paper, we establish a new volume comparison theorem for a complete manifold with a function $\rho (x)$ as the lower bound of the Bakry-Emery Ricci curvature. As applications, we obtain a new volume rigidity result of the gradient Ricci almost solitons. Furthermore, we extend the results of Cao and Zhou \cite{CZ} to shrinking gradient Ricci almost solitons and get the rigidity result with respect to the maximal volume growth.