Ozone (O₃) Measurement by UV Photometry
The principle of ozone measurement by UV photometry, air quality and calibration applications, and the ozone analyzers offered by Tetra.
Parameters measured with this method: O₃ (Ozone)
How does UV photometry work?
Ozone molecules strongly absorb ultraviolet light at around 254 nm. In a UV photometric analyzer, light from a mercury lamp passes through a measurement cell, and the light intensity is read at the detector. Measurement takes place in two stages: first reference gas passed through a scrubber that removes ozone, then the ozone-containing sample, is fed to the cell.
The ratio between the two light intensities is converted to ozone concentration using the Beer-Lambert law. Making reference and sample measurements one after another at short intervals eliminates deviations caused by lamp intensity and cell contamination.
What UV photometry measures and where it is used
The method measures ground-level ozone from ppb level. Main applications:
- Urban and rural air quality monitoring stations
- Multi-point calibration systems and ozone reference standards
- Verification of ozone generated by an ozonator
- Research and climate studies
Where UV photometry works well and where it struggles
UV photometry offers a direct, absolute measurement of ozone; because the absorption coefficient is known, no chemical reagent is used and very few consumables are needed. It provides a fast response and stable measurement.
Limitations: other components that absorb UV (some aromatic hydrocarbons, mercury vapor and some organic compounds) can interfere. Moisture changes and contamination in the measurement cell affect the result. Wear of the scrubber over time degrades the quality of the reference measurement, so periodic maintenance and calibration are required. It is important to choose a sample line material that does not consume ozone (for example PTFE).
Related standards
The UV photometry method for measuring ozone in ambient air is defined in EN 14625. Type approvals are assessed under the EN 15267 certification system.
Choosing an instrument for UV photometry
When selecting, the measurement range and options such as an internal sample/calibration valve, zero air source and ozonator are determined together. In air quality networks, periodically verifying the ozone analyzer in a traceable way against a primary standard increases data reliability.
Tetra and ozone analyzers
Tetra supplies, installs, commissions, calibrates and services UV photometric ozone analyzers in Türkiye. The product range includes Thermo Scientific 49i and 49iQ ozone analyzers. On the calibration side, the 49i-PS ozone primary standard calibrator and 146i/146iQ multigas calibrators are also provided by Tetra. These instruments can be integrated into air quality monitoring station cabinets.
Products using this method
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