Time-domain methods attracts much attention since a few years due to their ability to describe sound propagation in complex environments. However, such approaches requires a substantial computational power and a supercomputer remains still relevant for sound propagation simulations in huge domains. Graphics processing units (GPUs) are massively parallel computing environments, that are more and more used for scientific computations purposes. Among time-domain methods, the transmission line modeling (TLM) method is especially well adapted to this kind of hardware architecture. The paper presents an OpenCLTM implementation of the TLM method, this language being compatible with a wide range of available computational hardware, either with Central Processing Units (CPUs) or with GPUs devices. The algorithm is applied to evaluate the impact of various scenarios of vegetation cover on urban frontages and building rooftops within the framework of the VegDUD french project.