background level

The typical or ambient level of something (such as noise, radiation, or chemical concentration) that is naturally present in an environment, without any additional or artificial sources.

• 🇨🇳某种事物（如噪声、辐射或化学物质浓度）在环境中自然存在的典型或基准水平，没有额外或人为来源。

1. Ambient measurement C1 formal

   The normal or typical amount of a substance, radiation, or noise present in an environment without any specific source.

   • The background level of radiation in this area is safe.
   • Scientists measured the background level of carbon dioxide in the atmosphere.
   • The background level of noise in the city is higher than in the countryside.

   🇨🇳本底水平

2. Baseline for comparison C1 formal

   A standard or reference point used to compare changes or effects in an experiment or observation.

   • We need to establish a background level before starting the experiment.
   • The background level of pollutants was recorded before the factory opened.
   • Any increase above the background level indicates contamination.

   🇨🇳本底水平