A team of scientists from the Institute for Multidisciplinary Research in Belgrade has come up with an innovation they hope will help improve air quality in urban areas: the LIQUID3, which is also known as the "liquid tree."

The liquid tree is actually an aquarium, an urban photo-bioreactor, that purifies the air in urban areas where there is not enough space to plant natural trees. 

So far, three such liquid trees have been installed in Serbia — two in the capital, Belgrade, and one in the city of Uzice — and there are plans to "plant" more. There is also considerable interest from abroad.