Dobson Unit

{
  "id": "MLC-T-ENV-008371",
  "term": "Dobson Unit",
  "field": "Environment",
  "definition": "1. A measurement of column ozone levels. If 100 DU of ozone were brought to the Earth's surface, it would form a layer 1 millimeter thick. In the tropics, ozone levels are typically between 250 and 300 DU year-round. In temperate regions, seasonal variations can produce large swings in ozone levels. For instance, measurements in Leningrad have recorded ozone levels as high as 475 DU and as low as 300 DU. These variations occur even in the absence of ozone depletion, but they are well understood. Ozone depletion refers to reductions in ozone below normal levels after accounting for seasonal cycles and other natural effects. For a graphical explanation, see NASA's TOMS site (http://jwocky.gsfc.nasa.gov/teacher/basics/dobson.html).\n\n2. Units of ozone level measurement. measurement of ozone levels. If, for example, 100 DU of ozone were brought to the earth's surface they would form a layer one millimeter thick. Ozone levels vary geographically, even in the absence of ozone depletion.\n\n3. The unit of measure for total ozone or other gases. If you were to take all the ozone in a column of air stretching from the surface of the earth to space, and bring all that ozone to standard temperature (0 Celsius) and pressure (1013.25 millibars, or one atmosphere (atm)), the column would be about 0.3 centimeters thick. Thus, the total ozone would be 0.3 atm-cm, or 300 Dobson Units (DU).\n\n4. A measurement of column ozone levels, or how much ozone is in a vertical column of air. If 100 Dobson Units (DUs) of ozone were brought to the Earth's surface, it would form a layer 1 millimeter thick. Above the tropics, ozone levels are typically between 250 and 300 DU year-round. In temperate regions, seasonal variations can produce large swings in ozone levels. For instance, measurements in Leningrad have recorded ozone levels as high as 475 DU and as low as 300 DU. The DU is just one of many methods to measure ozone. Other measures include partial pressure, number density, and concentration of ozone, and can represent either column ozone or the amount of ozone at a particular altitude.",
  "abbreviation": "DU",
  "subject": "Health and safety",
  "references": [
    "SunWise Program Glossary",
    "Terms of Environment",
    "Glossary for UV Database",
    "Ozone Layer Protection Glossary"
  ],
  "url": "https://mlchart.com/terminology/environment/dobson-unit/"
}