Correction of Dasibi ozone measurements for the weak-line contribution

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Abstract
Measurements made by means of the Dasibi UV-absorption ozone photometer are customarily converted to ozone number densities by assuming that it is only the absorption of the strong 253.65-nm mercury-vapor line which is measured by the Dasibi. Paur and Ellis (EPA-600/4-79-057, September 1979) have shown that the Dasibi also measures the absorption of a number of the very weak mercury-vapor lines in the vicinity of the 253.65-nm line and that as a result the calculated ozone number densities must be increased by (0.5±0.5) percent. We have made measurements which show the dependence of this weak-line correction upon the lamp current and the lamp-housing temperature of the Dasibi UV light source, and have reduced the uncertainty in the correction by an order of magnitude. The weak-line corrections range from 0.33% to 0.74%.

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