Air pollutants are separated into two categories: primary pollutants and secondary pollutants.

污染物可分为两类别：主要染物及次级污染物。

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Igars and cigarettes, the primary source of ETS [environmental tobacco smoke], are smaller sources that emit pollutants near people and thereby exposures to ETS are very localized.

雪茄烟和香烟，这两个二手烟的重要来源只是靠近人体的污染源中的相对较小的来源，因此环境烟海的暴露度非常局限。

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But strict controls and transfer of pollutants to safe locations is a primary concern.

但是对发电站严格的控制和把污染物运输到安全的地点是主要的关注点。

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The government has had some success targeting primary pollutants, but analysts say it is just beginning to target secondary pollutant problems, including particulate matter that is harmful to human health.

WSJ: China's Pollution Fight Faces Resistance

China is particularly struggling to curb what are known as secondary pollutants, formed when primary pollutants such as emitted sulfur dioxide and nitrogen oxides, from coal burning and other sources undergo reactions in the atmosphere.

WSJ: China's Pollution Fight Faces Resistance