I feel your pain. There is a lumber manufacturer right next door to where I work and the wood dust just flies over the buildings and coats the cars every day. If you have a black car where I work you are screwed. At least my car in NFG still looks clean at least from far away.I have a long gravel driveway so my cars are always somewhat dirty. There's also a gravel lot a trucking firm operates from next to my work that coats everything in dust. Oh, and the garbage transfer station is on the other side of my work.
I run one or the other of my cars through a cheap automated touchless wash at least once a week.
I only hand wash a couple times per year, right before I apply sealant.