Q: Why do raindrops make your car dirty?
A: Wash your car on any given day and the chances of rain always seem to be pretty good. Raindrops typically leave a mosaic of grime that requires another trip to the neighborhood car wash.
Rain makes cars dirty, according to UW-Madison atmospheric scientist Steve Ackerman, because "the air near the ground has all kinds of particles floating in it: pollen, pollutants, dust, smoke, etc."
"As rain falls out of a cloud and down to the ground, it sweeps out and collects these particles into the raindrop. So, after the rain wets your car and then dries up, it leaves behind these particles on your car," Ackerman said.
The upside of the phenomenon, Ackerman points out, is that after a storm you might notice how clear the air has become. That improved visibility is because the rain has swept all those particles out of the air — and deposited them on your car.
— Provided in cooperation with University Communications