Yeah, I'm not quite sure what "Plein Air" is. You should probably ask and NPS ranger or an official who might know.
Sorry, I have no idea. Best to check with the park directly.
Hi Bernie, this is permissible without a permit. The only limitations would be: no painting in or on a monument, and you can't obstruct normal visitation patterns (set up in the middle of a road or walking path).
I'm not sure, sorry
It gets very busy in the park, you would need to stop at the visitor center and inquire at the desk if you're permitted to set up your equipment to do a landscape painting. They will be concerned about any litter and if you would get paint on anything besides the canvas. Also if allowed you need to not interfere with others view of that area.
Thanks! Your answer is awaiting moderation.