Dan Daher rolled out at 5 a.m. from the shaded parking lot behind the Torres Martinez Tribal Community Hall in Mecca, as he does every Sunday through Thursday. By day's end, he'll have logged nearly 300 miles in his Kia Niro hybrid, crisscrossing Southern California highways, dust-caked towns and badly potholed roads encircling the Salton Sea and the rural Imperial and east Coachella valleys. He’s driven through a cloud of tractor smoke on Highway 86 so thick he couldn’t see the road, and swarms of butterflies that coated his windshield in Westmoreland.

“Everyone thinks I’m Google,” he laughs. Not exactly.

He and other drivers in specially equipped cars are measuring air pollution block by block, microscopic fleck by fleck, around the clock near the contaminated and fast-drying Salton Se

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