Dozens of California cities, especially in the San Francisco Bay area, the Central Valley, and the southwestern coast, have created urban growth boundaries.

加利福尼亚州的几十个城市，尤其是在旧金山湾区、中央谷地和西南海岸，都已界定了城市成长边界。

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What ails Modesto is what ails Bakersfield (No. 1), Hanford (No. 3), Fresno (No. 4) and other small Central Valley cities (the Valley accounts for all the California cites on the list aside from Los Angeles): heavy doses of nitrogen oxide and hydrocarbons stemming from gasoline, chemical processing, paints and other industrial byproducts that harm the ozone and release particle pollution into the air.

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These findings will be of particular concern to cities in the Central Valley of California like Bakersfield and Fresno, which have for years ranked among the highest in the nation for air pollution.

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