By TAMMY WEBBERCHICAGO (AP) a¿¿ The images are startling. Billowing black clouds darken the daytime sky as wind-driven grit pelts homes and cars and forces bewildered residents to take cover. The onslaught, captured in photos and video footage from Detroit and Chicago this year, was caused by the same thing: brisk winds sweeping across huge black piles of petroleum coke, or "petcoke," a powdery byproduct of oil refining that's been accumulating along Midwest shipping channels and sparking a new wave of health and environmental concerns. The piles are evidence of a sharp increase in North American oil production a¿¿ particularly crude extracted from oil sands in Canada a¿¿ that has been trapped in the Midwest because of limited pipeline capacity to carry it to the Gulf and West coasts, leading to unprecedented amounts of oil refining and petcoke production here. In Midwestern neighborhoods near refineries, the growing black mountains have brought outcries from residents and new efforts by lawmakers to control or banish the blowing dust. "We could barely open the windows this summer because the black dust was so bad," said Susanna Gomez, 37, a mother and grandmother who lives on Chicago's far southeast side, across a set of railroad tracks from a shipping terminal that stockpiles petcoke until it can be loaded on to ships for export. She said she worries about one of her sons, who's asthmatic, but doesn't have the money to move. Alan Beemsterboer, whose family owns another nearby site that long has handled slag, asphalt and coal, and now, increasingly, petcoke, said he doesn't understand the controversy. "This has been an industrial area forever a¿¿ a coke plant used to be there, a steel mill used to be there," Beemsterboer said. "Coal and petcoke are just dirty words now. " Petcoke has been part of the American industrial landscape since the 1930s, when refineries began installing equipment to "cook" residue left over from making gasoline and diesel into a solid fuel that could be burned in power plants and cement kilns.