需要说明的是，沙子，是一种颗粒物质(PM)。测量空气污染物的不同组成成分含量等级时，它被归为颗粒物质。
It must be noted that sand is a 'particulate matter' (PM) and is recognized as such when measuring levels of the many different components that make up air pollution.
需要说明的是，沙子，是一种颗粒物质(PM)。测量空气污染物的不同组成成分含量等级时，它被归为颗粒物质。
It must be noted that sand is a 'particulate matter' (PM) and is recognized as such when measuring levels of the many different components that make up air pollution.
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