Background levels

• 背景值

Background levels的用法和样例：

例句

1. The background concentrations of ambient air pollutants were used as evaluation stan-dards.
   采用大气污染物浓度的背景值为评价标准。
2. In the Campania region, baseline and background values are often coincident, where the samples represent catchment basins away from urban or industrial areas.
   在坎帕尼亚地区，样品代表的是远离市区或者工业区的汇水盆地，所以基线值和背景值经常是吻合的。