Being raised in a rural village in Belgium, living in the busy and polluted city of Barcelona makes me crave for some fresh air every now and then. I am certainly not the only one. 90% of the world’s urban population is breathing polluted air. Sometimes called the silent killer, air pollution is responsible for nearly half a million premature deaths a year in Europe alone. I know everyone is freaking out about ISIS right now, but the real killer is all around us and we have created it ourselves.

A CityTree installed in Oslo is drawing attention (photo: Oslo Phototour)