The problem is most acute in the Central Valley, where nearby mountains tend to trap the pollution sent to the skies from heavy auto traffic and other machinery.

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"As a public company, stock is our currency, " explains the company's chief, Steven Schneider, who took the top job when Zap, which stands for "zero air pollution, " bought Schneider's auto repossession business in 2002.

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Some experts think the global auto market may actually have maxed out, due to concerns about pollution and sprawl, as I wrote for Forbes earlier this year.

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Hydrogen has the virtue of removing the auto industry from the environmental debate, even if it creates the same or more pollution upstream.

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Mr. BECKER: This is a cynical effort by auto companies to evade the law that would reduce our oil dependence and global warming pollution.

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Not only do commuters in Southern California inhale the worst year-round particle pollution levels, but Riverside drivers also face the highest rate of fatal auto accidents per capita, and Los Angeles drivers spend the most time sitting in traffic.

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