Trees outside a building containing frescoes in Italy and lichen inside the building are protecting those frescoes:

https://www.sciencedirect.com/science/article/pii/S004896972200821X?via%3Dihub

Pollution caused by the local vehicles is collected by the plants. These pollutants do accumulate on the art work but when the trees capture the pollution before it gets into the building it protects the art.

I find that very interesting.