This paper presents a new method for odor source localization using a Wireless Sensor Network (WSN) by means of collaboration with a mobile robot. The method has two steps: an initial estimation of the position of odor-source is obtained centrally by one robot and is based on particle filtering. It does not require any prior information about the position of the nodes. In the second stage, the nodes refine their position estimates employing a decentralized information filter. The paper shows how the method is very suitable for outdoor odor-source localization with robotic systems. The paper includes several implementation aspects and experimental results.