Pollution is nowadays emerging as a major threat for the human being. Cities’ sizes are increasing, as well as the number of inhabitants living in urban areas. Therefore, air pollution monitoring becomes an important concern for the scientific, medical and political world. This paper describes a scalable architecture for monitoring air pollution in large areas where collected data will be represented through an Internet interface. The proposed solution is based on the presence of multiple sinks in the Wireless Sensor Network (WSN). An algorithm to optimize the placement of sinks is presented.