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While Twitter and other Online Social Networks (OSNs) or microblogs are considered as a source of information for breaking news or uproarious and unexpected events, they could also be exploited as a dense worldwide sensors network for physical measurements. The corpus of geotagged posts from OSNs includes people’s feedbacks about a wide range of topics, with precise temporal and geographical metadata, that can be used as a support or an improvement to hardware sensors. For instance, if collocated people, independently and at the same time, write posts complaining about high temperatures, it could effectively denote a raise of heat in that place. In this paper, we explore the feasibility to use a geographical search on social networks, that is, a geosocial search, about air pollution related posts, as effective air impureness measurements. We evaluate our assumption in large cities over three continents of the planet, where a minimum increment about the number of air pollution related posts in an area, indeed corresponds to a raise of minimum pollution values in such area. Such a correlation can be exploited to integrate and extend existing air pollution monitoring networks. At the end of the manuscript we propose to further employ the time series of posts returned by the geosocial search to predict next pollution values.

Vehicles provide an ideal platforms for a plethora of emerging applications such as networked gaming, multimedia content delivery and urban sensing. Cars have no power constraints and they can be instrumented with high end computational units and graphic devices. The deployment at scale of urban vehicular systems, however, requires a careful design able to consider challenges across several domains. Vehicular systems are arguably a prominent example of cyber-physical systems. The development of such systems requires a truly multidisciplinary approach and a close integration between the application, communication, and physical domains. Hardware and software mounted on vehicles will face a harsh physical and communication environment that will greatly affect all the system components. In this paper we report on the challenges and opportunities for multimedia vehicular urban sensing systems based on our field experiences in Macao (China) and Los Angels (USA). We designed and built the components for a pollution monitoring system able to support closed-loop optimization between pollution and traffic management. Our initial set of prototype vehicles are now running in the city of Macao and they are measuring the air parameters as well as the urban traffic. The paper aims at exposing some of the issues encountered, outlining the problems of a city wide deployment, and augmenting our in-field experience with the results from large scale simulation studies. © 2012 Elsevier B.V.