A general view taken on July 26, 2021 shows an AirBubble, an innovative playground providing clean air thanks to algae that absorb pollutants and carbon dioxide and in return produce oxygen, in Warsaw, Poland. - At the new playground in central Warsaw, algae feast on pollutants and carbon dioxide to provide a bubble of clean oxygen in a city ranked as one of the most polluted capitals in the EU. The Polish capital was selected for the inaugural edition of the AirBubble as the city is in particular need of clean air. According to data released by the European Environment Agency (EEA) last month, Warsaw ranks 269th for air quality on a list of 323 European cities. The bubble is outfitted with dozens of glass cylinders containing algae immersed in water that feast on air being pumped in from below. The green organisms consume polluting molecules and carbon dioxide before releasing clean oxygen out the top of the bioreactors. (Photo by Wojtek RADWANSKI / AFP)