Anyone seen this type of dirty/smoky discoloration? It’s not moisture. Second story, but no attic access.
You are the man! Much appreciated!
Yes. Have those stains in my apartment on inner drywall on masonry bump-out walls that protrude the average envelope dimensions. Thermal bridging or thermal tracking. Can be referred to as Ghosting stains.
The staining is the slow buildup of atmospheric air-borne dust, dirt, soot particles or even microbial growth on walls or ceilings. Warm air-borne atmospheric dust, dirt, soot particles attracted to, clinging to cold areas. The cause, candles are one culprit.
Likely air entering the roof framing via loose coping. Loose coping may lead to masonry issues at the parapet. Leaning. Degrading mortar.
Add degraded windowsill masonry and window frame caulking loss, gaps between the window and framing members, and the envelope is setup to allow weather to enter between the out/inner wall assembly causing buckles and bowed walls.