They recommend revised limits for the concentration of selected air pollutants: particulate matter (PM), ozone (O3), nitrogen dioxide (NO2) and sulfur dioxide (SO2), applicable across all WHO regions.
它们为下述选定的空气污染物的浓度限值提出了修订：可吸入颗粒物(PM)、臭氧(o3)、二氧化氮(NO2)和二氧化硫(SO2)，适用于世卫组织所有区域。
The concentration of nitrogen trifluoride in the atmosphere is about 0.5 part per trillion, making it very hard to measure.
大气中三氟化氮的浓度大约为0.5万亿分之一(ppt)，使得它很难测定。
With the increasing of oil migration effects, the concentration of nitrogen compounds decreased whereas the ratios of shielded nitrogen compounds to exposed or semi-shielded ones increased.
随着运移作用的加强，含氮化合物绝对浓度下降，“屏蔽”型与“暴露”型或“半屏蔽”型化合物的比值增加。
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