Noise pollution has become a serious social problem in many cities.  Noisetube.net is an ongoing project aimed at monitoring the noise pollution exposure as experienced by urban citizens using a participatory approach. Thanks to GPS built-in mobile phones used as an environmental sensor to capture the decibel, localization but also user's impression inputs, any citizen concerned with urban noise can measure, share their daily noise exposures with the community and visualize the collective result on the city's map. 
Of course there are technological challenges to develop tools for non-experts. In particular getting credible decibel measures from a cellphone whereas the use of professional sound level meter is normally required is a real one. Furthermore we also added a tagging feature on the mobile application to tag noise sources and add a layer of meaning on top of the physical measures. Mixing physical and semantic measures will also be a challenge.  But beyond this technical aspect  the use of mobile phone as an environmental sensor to gather environmental data empowers communities to build local campaign without waiting formal projects. Like the web 2.0 "user-generated content" was made possible thanks to new publishing tools (e.g. blog)  for newbies, these "citizen-generated measures"  open a new approach for the management of urban commons.