What Makes Dirt Stick?
As you drive, and even while you are parked outdoors, dust and dirt blow around and land on the car. Now, believe it or not, even on a dry day, and especially overnight, there is moisture in the air. Unless you live in an absolute desert, there is going to be moisture. When that moisture hits the dust that has settled on the finish, it makes it sticky, and you cannot now “blow it off.” After a few days or a week, depending upon your climate and how much dust is blowing around, you will notice a dirty film start to appear, even though the car may not yet look very dirty from any distance.
Even in a large city, where all the natural dirt is pretty well paved over, there is still dirt and dust blowing around. The source, instead of Mother Nature’s dirt may be particulate matter from bus exhausts; construction debris; rubber dust from all the tires on the roads themselves, and so forth. These kinds of dirt are even stickier than “regular” dirt, and stick by themselves without the help of moisture. Add the moisture, and you have a very dirty car. That dirt is damaging to the finish.
There are also run-ins with those rude birds who never like the color of any car, and try to re-paint it to their own tastes. Bird poo is highly acidic, and will etch the clear coat and paint. Get it off as soon as you notice it, even if it is not a regular wash day.