ppm
noun [ U ] uk/ˌpiː.piːˈem/ us/ˌpiː.piːˈem/
百万分之…(衡量物质与液体或其他物质混合时的度量单位,parts per million的缩写)
abbreviation for parts per million (= a unit for measuring the amount of a substance that is mixed with a liquid or another substance)
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