Just a thought, dirt comes from the car, and the person spraying the car because of static electricity.
Ground car, wear a cheap tyvack suit and a $2.00 head sock, and see the difference.
I have no filters and never wet the floor.
This is my play garage, I have built engines,
Converted brake systems and seviced auto trans in it.
I control airflow with the drive-in door.
Basecoat about 4 inches up from cement.
Clear about 1 inch up from cement.
Of course, this defies everything but for 24 years, I would pick this to paint vs a $150,000 paint booth.
Oh back in the day when I built the garage id have went a whole lot bigger say a 7 or 9-car garage.