The National Institute of Standards and Technology (NIST) has developed the Standard Reference Photometer (SRP) for ozone measurement traceability in collaboration with the U.S. Environmental Protection Agency (USEPA). Since 1983, NIST has provided SRPs to 22 international laboratories in 18 countries and several to the International Bureau of Weights and Measures (BIPM) as an ozone reference standard under the International Committee for Weights and Measures (CIPM). A pilot study in 2005 involved 23 laboratories to assess ozone comparability.
The SRP system has been upgraded to improve stability and operational control. An in-depth BIPM study identified temperature measurement biases causing an underestimate of ozone mole fractions by 0.4% and optical measurement biases overestimating mole fractions by 0.5%. NIST developed an instrument modification to reduce or eliminate these biases, upgrading 20 SRPs and producing 4 new SRPs with the new modification. The overall bias improvement in upgraded SRPs has shown agreement from 0.72% to 0.33%.
Keywords: quantum, measurement, sensors
