Persistently elevated levels of fine particle pollution are common across many urban areas. Fine particle pollution often originates from combustion sources such as power plants and motor vehicles.

在许多城市区域，常常出现细小颗粒污染程度呈持续性增高情况。细小颗粒污染通常来自发电厂和机动车等燃烧源。

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In all three places, fine-particle pollution also fell on Sundays, as did ozone in the summer months.

在这三个地方，周日的细微颗粒物污染也更少，就好像在夏季臭氧浓度也会减少一样。

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The group's recent "State of the Air" report said Pittsburgh has the worst short-term fine particle pollution in the country.

VOA: special.2009.07.13

But one of the biggest reasons for Phoenix's high pollution levels is actually cattle ranches found south of the city, in Pinal County and vicinity.. "Those cattle ranches are contributing a lot of fine particle pollution to the small communities near them that are part of the Phoenix metro area, but also to the tribe adjacent to it, " says Nolen.

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