Feasibility Analysis of Certifying Ozone Generators as Level 4 Transfer Standards

Kevin P. Mishoe1, Christopher M. Rogers2, Michael J. Smith3 and H. Kemp Howell3

During 2009 and 2010, MACTEC investigated the feasibility of certifying a Thermo Scientific 49i ozone analyzer's internal ozone generator as an onsite Level 4 Transfer Standard as described in 40 CFR Part 58 by correlating generator lamp voltage to output concentration. The primary advantage of this design includes deployment of a single monitor including both the certified generator and the site photometer, allowing lower up front deployment costs. Each generator was certified by running a six point audit against a certified Level 3 ozone detector on six different days within a two week period and periodic re-certification audits at least semi-annually once installed in a field location. This study examined two methods for operating the ozone generators and results from a field evaluation. The first method used a pressure regulator and a critical orifice to control air flow through the generation chamber. This method was found to have a direct dependence on the ambient atmospheric pressure and could only be considered at sites with similar altitude to the original certification location. The second method utilized a pressure regulator and critical orifice to control the mass flow rate and a flow controller to control the volumetric flow rate of the air leaving the generation chamber. By doing so, both the initial oxygen mass concentration and residence time in the generation chamber could be controlled. This method did not depend on atmospheric pressure and could be evaluated for use at any location. Both methods were ultimately limited by the overall stability of the ozone generator's ultraviolet lamp over long periods of field deployment and were shown to be less stable than using a separate certified ozone detector as the onsite transfer standard.

1 MACTEC Engineering & Consulting, Inc., 404 SW 140th Terr., Newberry, FL 32669, 352.333.2602,
2 MACTEC Engineering & Consulting, Inc., 3901 Carmichael Ave., Jacksonville, FL 32207
3 MACTEC Engineering & Consulting, Inc., 404 SW 140th Terr., Newberry, FL 32669