The main objective of this research is to avoid the release of water vapor from the fuel cells into the atmosphere. In hydrogen aircraft, water may be stored or even used. But in Unmanned Aerial Vehicles (UAVs) it needs to be discharged into the atmosphere. Water vapor has an intricate effect on global warming. Increased water vapor in the atmosphere amplifies the warming caused by other greenhouse gases. Water vapor convectively injected into the mid-latitude lowermost stratosphere could affect the stratospheric ozone. The associated potential ozone loss process requires low temperatures, together with elevated water vapor mixing ratios that extensive UAV traffic may trigger.