Scott Denning, a climate scientist at Colorado State University, says ozone forms “downwind of where it was created,” and lists the ingredients as “unburned fuel from gasoline, nitrogen oxide and sunlight.” He said it’s understandable that Sequoia would have a level of 90 ppb because it’s “between the L.A. basin on one end and the Bay Area on another – 20 million people can produce enough [pollution] and it’s a sunny place and can cook it in the air and drift upwards.”

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