YVR released an online web tracking tool that allows members of the public to see real-time and historical flight and noise data collected by the Airport Authority’s aircraft noise monitoring and tracking system.

What does this have to do with Splashes? Well I think it explains a lot.
While you’re at the above site, set the time back a couple of hours and turn the speed to x10. Watch the number of planes continuously flying above us.
Red planes are landing, green planes are taking off and the yellow ones are unknown aircraft. Probably private planes out of Boundary Bay Airport.
You’ll notice a constant stream of red planes flying over Surrey on their way to land in Richmond. Next a lot of the planes taking off turn and fly over Delta and South Surrey.
Now the next time your car is clean, but has not been washed in a few days, wipe it gently with a white tissue. Even though your vehicle looks clean, you should see black soot on the tissue.

This is a sticky film that wash soaps have a really hard time penetrating. It is fallout from the air traffic, pollution, salt from our ocean and the regular road contaminates all combined with our acidic black soil.
This is why the Lower Mainland is one of the most difficult places for a carwash to properly clean a car.