Air pollution burdens the environment and people's health, particularly in cities. Yet many urban centres don't have enough space or money for more trees and parks. With CityTree, the Dresden start-up Green City Solutions has developed a special green area. The mobile vertical green space provides room for moss and blossoming plants that absorb fine dust. At the same time, it functions as a WLAN hotspot and advertising medium. Logos and QR codes can be represented on it with plants or plastic pixels. Another plus: the multifunctional plant system records data on air pollution control thanks to sensor and remote maintenance technology. A sustainable project that benefits citizens, companies, and the environment.