5.2.1 Principle
In ambient air monitoring applications, precise Ozone concentrations called standards are required for
the calibration of Ozone analysers. Due to the instability of Ozone, concentrations must be generated
and “verified” on site with another instrument referred to as a transfer standard.
A transfer standard is defined as a transportable device or apparatus which is capable of accurately
reproducing Ozone.
The transfer standard’s purpose is to transfer the authority of a Level 1 pollutant standard to a remote
point where it is used to verify or calibrate an air monitoring analyser.
The U.S. EPA identifies the family of standard reference photometers (SRPs) as Level 1 standards.
Beyond the SRPs, all standards are considered transfer standards and are numbered (starting with 2)
based on their “distance in the traceability chain” from a verification against a Level 1 standard. With
each additional level, the number of standards available is added to. Each standard is traceable through
a chain of “higher” standards to the Level 1 standard.
Figure 100 – Ozone Transfer Standard Hierarchy
The majority of transfer standards include both Ozone generators and photometers. Therefore, it is
strongly suggested that:
Level-2 standard is used in the verification of other transfer standards include both an O3
generation device and a photometer (e.g. Serinus Cal 3000).
Level-3 standard be, at a minimum, a photometer (Serinus 10). The level 3 standard can be a
photometer and generator (Serinus 10 and Serinus Cal 2000 or Serinus Cal 3000) but should not be
just a generator.
Level-4 standards are an Ozone generation device (e.g. Serinus Cal 2000).
Ozone Transfer Standards also require routine calibration against a higher transfer standard. The U.S.
EPA recommends the following calibration frequencies.
Regional Standard Reference Photometer – once per annum.
Ozone Level 2 Transfer Standard – once per year or after repair.
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