Again trees and air quality:
This is another study that proves the benefits of planting trees and bushes in cities. For a person who lives in Madrid, the importance becomes higher. Also, if you see the picture in the link below, you can see the last project done by Leandro Sliva in Madrid, in torre Picasso. This is a part of the abstract:
"Trees, bushes and other greenery growing in the concrete-and-glass canyons of cities can reduce levels of two of the most worrisome air pollutants by eight times more than
previously believed, a new study has found".