I'm clean when I'm black, Dirty when white; Get too close, And you might sneeze. What am I?

Question

I get dirty in about 5 days but it takes half an hour to clean me.
It takes a long time for me to be tall but I can be short in about 5 seconds.
What am I ?

Answer 1

Thanks for the query.

The answer is - A chalkboard or a blackboard.

Answer 2

Are you a Dusty chalkboard