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The Dobson unit (DU) is a unit of measurement of the amount of a trace gas in a vertical column through the Earth's atmosphere.It originated by, and continues to be primarily used in respect to, the study of atmospheric ozone, whose total column amount, usually termed "total ozone", and sometimes "column abundance", is dominated by the high concentrations of ozone in the stratospheric ozone layer.
The study of ozone concentration in the atmosphere started in the 1920s. ... grade ozone generators, these units usually work by means ... will convert atmospheric ...
Thus, ozone is mainly removed by ozone conversion. Both ozone creation and conversion depend linearly on oxygen atom concentration, but in ozone creation an oxygen atom must encounter an oxygen molecule and another air molecule (typically nitrogen) simultaneously, while in ozone conversion an oxygen atom must only encounter an ozone molecule.
Air pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude. The concentration decrease is directly proportional to the pressure decrease with increasing altitude.
For example, such a regulation might limit the concentration of NOx to 55 ppmv in a dry combustion exhaust gas corrected to 3 volume percent O 2. As another example, a regulation might limit the concentration of particulate matter to 0.1 grain per standard cubic foot (i.e., scf) of dry exhaust gas corrected to 12 volume percent CO 2.
If all of the ozone in the atmospheric column one was measuring were compressed to STP, the thickness of the compressed atmosphere in mm would equal an answer in Dobson Units divided by 100. The vertical distribution of ozone is derived using the Umkehr method. This method relies on the intensities of reflected, rather than direct, UV light ...
The median PFHxA concentration was nearly 800 parts per billion (ppb), but one sample had a concentration of more than 16,000 ppb. (By comparison, ...
The air quality index is a piecewise linear function of the pollutant concentration. At the boundary between AQI categories, there is a discontinuous jump of one AQI unit. To convert from concentration to AQI this equation is used: [41]