Our area is very dusty in the summer. There are a lot of "back roads," all of which are unpaved gravel. We live on a gravel road off the main highway.
When it's hot and dry, dust gets kicked up when you drive down a gravel road. Harvest also creates dust. Combines stir up tons of it as they chop through the wheat and then spit chopped straw and chaff out the back end, having sifted the wheat from the chaff.