According to how the other half lives, where did the only fresh air for tenement rooms come from?

"From either the hallway or the stairs".

How the Other Half Lives: Studies among the Tenements of New York (1890) is the full name of the publication and it is a production which is termed as photojournalism by Jacob Riis, recording dingy living conditions in New York City ghettos in the eighteen-eighties. It filled in as a reason for future "muckraking" reporting by presenting the ghettos to New York City's upper and white collar classes.

if you tell me the video, i may be able to answer your question.