sorry that sounds a little preposterous, but you know perhaps if you have a wintry mix of snow/rain, it looks a little slushy as you wipe it from your glass windshield? Or if you are driving behind a Tractor Trailer on the Pike after a blizzard, and your windshield is just coated with a salty sludge? It was like that, except just with the precipitation that collected on my car on Wednesday and again through this morning's weather. The rain seemed to leave a filmy, or grimy streak/residue. When driving, we were prompted to wash the windshield noticeably often. Again I have no information that it's related to pollution but it just looked like rain but did not run off, wipe off, bead up etc. the best way I can describe it was that it was just not as wet. more viscous.