Background level

{
  "id": "MLC-T-MET-003766",
  "term": "Background level",
  "field": "Meteorology and atmospheric science",
  "definition": "The concentration of a substance in the atmosphere or environment that is naturally present or results from widespread, diffuse sources, rather than a specific local emission. It represents the baseline concentration against which localized pollution events are measured. Background levels can vary geographically and temporally.",
  "see_also": [
    "ambient air"
  ],
  "url": "https://mlchart.com/terminology/meteorology/background-level/"
}