Can Mexico City's roof gardens help the metropolis shrug off its smog?

The azotea verde atop the circular single-story offices of the botanical gardens, is planted with hardy stonecrop, which can withstand the Mexico City summer, but which also produces oxygen and serves as a filter to draw out the carbon dioxide and heavy metal particles in the air. As well as providing the park's squirrels with an arena in which to practise their parkour, the roof help regulates the temperature of the offices below and soaks up rainwater to keep the building dry.