The agency has struck a deal with the poster company VanWagner, which will see two super-sized posters go up on its sites in and around London over the next two months. Planning will be handled by VanWagner.
One of the posters, shot by the acclaimed photographer David Bailey, shows the ex-Madness singer Suggs wearing a leaf as a breathing strip across his nose, with the strapline: "Breathe in London. The ad was written and art directed by Mitch Levy and Tony Kielty.
The other poster, shot by Rolph Gobbitts, shows a fully grown oak tree standing next to a small artificial Christmas tree.
The copy reads, "A poisonous gas extractor and a tree", and was created by Ben Akers and Katrin Hanusch.
VanWagner's sales director, Kevin Shute, said: "We stand behind the aims of Trees for London, and we have found ourselves in a position to help a charity we admire."
Trees for London's chief executive, Graham Simmons, added: "TFL will benefit everybody, and our two posters aim to reinforce what trees do for all of us."