Water Vapor Interference in the UV Absorption Measurement of Atmospheric Ozone

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Courtesy of 2B Technologies

In this thesis work, a significant and sometimes large water vapor interference inherent to many and possibly all UV-based, commercially available ozone monitors was positively identified for the first time.  Depending upon the instrument's recent atmospheric history and calibration method, zone monitors can give erroneous results both immediately and hours later, and as a consequence possibly affect the apparent compliance of municipalities with EPA ozone regulations.  Deviations from true ozone concentrations result from modulations in the water vapor concentration within the cell and between I and Io measurements as a result of the ozone scrubber (usually hopcalite or a similar material) acting as a water vapor reservior, alternately drying or humidifying the air stream flowing through the absorbance cell.

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