举例来说，1997年，美国环保署意图降低地表臭氧量标准——一种部分由石油精炼排放的污染物造成的污染。
In 1997, for instance, the E.P.A. moved to reduce surface ozone, a form of pollution caused, in part, by emissions from oil refineries.
地表臭氧和颗粒污染物是人类健康的最大威胁。
Ground level ozone and particle pollution are the greatest threat to human health.
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