It's hard to find room in the middle of a city to plonk down enough trees to make any appreciable dent in the amount of pollution. Instead of trying to clear space for a new park, the city of Milan has decided to take their forest vertical with a pair of 25 and 35 story buildings completely covered in trees.
The Bosco Verticale (Vertical Forest) project may be concepty looking, but construction has already started in downtown Milan. When completed, there will be two residential towers, each covered in balconies planted with 900 trees along with a pleasing selection of floral plants and... shrubbery. This will end up as the equivalent of about two and a half acres of forest, albeit without the native population of mountain lions and bears and killer bees and such.
In addition to adding some refreshing greenness to an urban center, the Vertical Forest buildings will filter out CO2 and dust particles, produce oxygen, help regulate humidity and temperature, and provide a valuable habitat for mountain lions and bears and killer bees and such. Irrigation will come largely from grey water from residents of the building, all of whom will have a tiny little forest on their balcony. I'm not sure how much rent is going to be in a place like this, and I'm guessing it's more (way more) than a poor old blogger can afford, but if buildings like this become the norm instead of the exception, maybe one day people like me will have a shot at a high rise apartment with a private patch of woods.