What is the fine-grained topic of the following text: By encouraging more architects and urban planners to follow the lead of visionary architects like Stefano Boeri Architetti who gave us the world's first 'Vertical Forest' building, Bosco Verticale, in Milan (Milan is one of the most polluted cities in Europe). Only return the topic.
Encouraging architects and urban planners to follow visionary architecture like Stefano Boeri's 'Vertical Forest' building for pollution control in cities.