Participatory sensing, when a crowd of users collaborate to collect useful information, based applications are getting popular these days thanks to the proliferation of powerful mobile devices. The built-in sensors of smartphones offer an easy and handy way to monitor the environment and collect data which can serve as the basis of smart applications. However, the quick and flexible development and deployment of these applications call for a unifying open architecture. In this paper we propose a publish-subscribe based open participatory sensing architecture.