Improvement of the quality of the ozone measurements by means of a standard reference photometer

Abstract

The Directive 92/72/CE makes reference to the analysis method described in the UNE 77-221:2000 and to the fact that the ozone analyzers shall be calibrated with a UV reference photometer or with a transfer standard.

From the need of developing a procedure that assure the quality and the trazability of the measurements in Spain, the Atmospheric Pollution Area has decided to implant a NIST UV reference photometer as ozone national standard.

Taking into account the procedures used by EPA and NIST, a verification procedure has been developed consistent in the realization of 6 comparisons of the Transfer Standard versus NIST UV reference photometer in different days; at least 5 different ozone concentrations are analyzed. Each comparison begins and ends always with a concentration of 0 ppb of O3, and from each comparison its regression linear is obtained.

Once the 6 comparisons are done, the calibration relationship is obtained and the uncertainty associated with the transfer standard is calculated.
Until now, the verifications of 17 transfer standards have been done: 11 of them were UV photometers, 2 were ozone generators and 4 were ozone generators of dilution banks.

From the results is concluded that generally the uncertainties of the ozone generators are greater than those of the UV photometers, so being recommended this one like transfer standard.

To emphasize that with the utilization of the tranfer standards for the calibration of ozone analyzers, the quality and the trazability of the generated data are guaranteed.