Participatory sensing (PS) platforms enable stakeholders to collect, analyse and visualise data for a particular interest. Despite high societal demand, developing a new PS platform remains a labour-intensive, nonreusable process that requires high technical expertise. We present DISCOPAR, a visual reactive flow-based domain-specific language geared towards the construction of reusable citizen observatories. With DISCOPAR, users interact with visual components to implement the various elements of a PS platforms without having to worry about its underlying technological complexities. We validate our approach through experiments using real-world empirical usability studies of ICT-agnostic users. The results show that DISCOPAR allows users with limited technological knowledge to create their own PS platform.