In April 2011, we launched the CitySee system as the extention of GreenOrbs into urban CO2 monitoring area. CitySee inherits the self-organizing WSN technology of GreenOrbs. The goal of CitySee is to deploy thousands of wireless sensor nodes in an urban area of Wuxi City, China, such that multi-dimensional data including CO2, temperature, humidity, light, location, and etc. could be collected in a real-time manner for further analysis. The main applications of CitySee include measuring the carbon absorbance and emissions in different zones of a city, supporting the government’s policy decision in energy saving and emission reduction, and offer citizens with convenient daily living services.