For several weeks.... a thick black residue has been falling from the sky, blacking out the sky & even windows.
City authorities say, " It is tree SAP, insect residue "
* This is All ,I could find... not much *

YouTube - news

http://youtu.be/o1Mr8g5E_Lc/

Chicago News

http://www.nbcchicago.com/news/local/Sticky-Residue-Coating-Cars-in-Elk-Grove-Causes-Stir-Among-Residents-321318371.html/

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Sticky Residue Coating Cars in Elk Grove Causes Stir Among Residents
By Emily Florez

Frustrated Elk Grove residents whose cars and other outdoor possessions are covered in a mysterious film are complaining about the damage as village officials release a statement about what they believe is causing it. NBC 5's Emily Florez reports. (Published Monday, Aug 10, 2015)

Frustrated residents in suburban Elk Grove have complained about a sticky residue that has coated their cars and anything else kept outside that some believe may come from jets or nearby construction.
Elk Grove Village officials released a statement Monday that claims the mysterious film is actually caused by sap, however. Their information comes from an "expert forester," they said.

"Due to the wet spring, there has been higher than usual sap production and activity by scale insects, which consume sap and cause residue to be released into the air," a statement from the Elk Grove mayor's office read. "While the sap residue is clear, fungi attracted by the residue as well as dust and other particles in the air can give it a blackened appearance. The recent dry spell means that no rain has rinsed away this residue, and the sap residue continues to blow around, collecting on cars and other surfaces."
Some residents do not believe a sap is the cause for the mysterious residue, however.
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"I don't believe that at all," Elk Grove resident Amy Lucarz said. "We have had plenty of wet springs around here. ... It just doesn't add up."
Elk Grove resident Peggy Passaro describes the film as "sticky" and "tacky" and says it gets worse as humidity increases.

Lucarz, who has lived in Elk Grove for 11 years, said she has never seen the dark residue before. Within just a couple of hours of washing her vehicles, toys and furniture, they are completely covered again, she said.
The film is dark enough that Passaro has a difficult time seeing out of the back window of her car, especially at night, she said.

The problem has persisted for several weeks now, and residents who are skeptical of the village's response continue to wonder what could cause it.
The FAA has not released a statement about the possibility of jets as the cause of the film, but they encourage residents to call in a report at (847) 294-7900.

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Another mini mystery... I have copied the link repeatedly & it is NOT posting as a workable link

Journal & Topic Newspapers For Elk Grove Illinois

http://m.journal-topics.com/news/elk_grove_village/