Cement plants are big air polluters and in 2009 industrial giant Cemex wanted to build a new plant near the Grand Canyon, causing concern about increasing the haze that already plagues the national park. We revisit a report by Arizona Public Radio’s Laurel Morales, and host Steve Curwood catches up on the story with environmental engineer Bill Auberle who discusses current threats facing the iconic attraction and hopeful signs for its future. (published April 1, 2016)