John it doesnt matter what it is, but consider the alternatives. Personally , i would rather remove the light deposits, than park it in the sun, but then you have to deal with bird crap, so 6 of one, 1/2 dozen of another.....(I park under the trees.....)
I suffer the same problems where i live, we have huge pine trees, that drop pollen, sap, and big green pine cones, and blossomed pine cones. We have sycamores also, they excrete some sort of sap, could be a described above, although i havent seen any real significant insect population, so i deter my belief to sap excretions.
For some reason i prefer sap to U.V.'s.