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SRI 6008 Ozone Standard Reference Photometer

Technical Contact:  James Norris 

The NIST Standard Reference Photometer (SRP) is a photometric instrument that accurately measures concentrations of ozone (O3) in air up to 1000 nmol/mol by absorption of the 253.7 nm mercury line.The measurement principle is based on application of Beer-Lambert Law using an absorption cross-section of 1.147 x 10-17 cm2/molecule.The NIST SRP design is a dual-cell system where the charging of each cell alternates between sample and reference sample streams. The measurement procedure uses a variable-length instrument cycle which minimizes the effects of lamp drift and absorption cell/detector biases.Comparisons spanning the past 30 years show agreement within 1 percent over the 0-1000 nmol/mol molar fraction range.New NIST SRPs typically agree with NIST SRP 2 (NIST's highest level ozone standard) to better than 0.3 %, and historically the one-standard-deviation spread of all NIST SRPs vs. NIST SRP 2 is 0.7 %.The SRP system includes an internal ozone generator and an automated control system which allows for automatic measurements against other NIST SRPs or calibrations of commercial ozone instrumentation via serial communication or analog signal measurement.

Currently, the NIST SRP serves as an International Reference Standard and is used by the Bureau International des Poids et Mesures (BIPM) as a reference for ozone measurements. International traceability to the SI for ozone measurements can be obtained through the BIPM or NIST.

Specifications Certificate (PDF format)

The prices listed below are for the individual instrument and do not include costs related to the final measurement calibration performed before delivery or post-delivery installation and training.  The related Calibration Service ID for the SRI is 37530C.  To obtain a nist-quote for the instrument and calibration services, please contact Sales and Customer Service by phone at 301-975-2200 or email at


Ozone Standard Reference Photometer


Created September 28, 2016, Updated January 28, 2020