I’m looking for a book I read in the seventies (or maybe 1980), it was a children’s book about kids that lived in a high rise and never went on the streets because of too much pollution/a ruined world. They may have gone outdoors only once a year. They may have worn gas masks or breathing masks. I remember dark illustrations and it being a cautionary tale. I believe that all the remaining world’s population lived in one high rise building. I think there may have been one remaining plant or flower and that going to look at it was extraordinary/special. Definitely a picture book.