Questions & Answers about yījià zài yángtái shàng.
Because they do different jobs.
- 在 introduces the location: to be at / in / on
- 上 is a localizer attached to 阳台, giving the exact spatial relationship
So 在阳台上 is a very common Chinese pattern:
在 + place + localizer
Here, 阳台上 means on the balcony / at the balcony area.
Not really. In this sentence, 上 does not mean up in the motion sense.
After a noun, 上 often works as a location word meaning something like:
- on
- on top of
- sometimes more loosely at
So:
- 桌子上 = on the table
- 墙上 = on the wall
- 阳台上 = on the balcony
With place words, 上 is often less literal than English learners expect. 阳台上 just means the balcony area, not that something is sitting on top of the balcony structure itself.