Name two common methods for measuring ozone in ambient air.

• A. UV photometric ozone analyzer (UV absorption) and DOAS (differential optical absorption spectroscopy) for ozone.
• B. Chemiluminescence and IR spectroscopy.
• C. Gas chromatography only.
• D. Mass spectrometry and NDIR.

Answer: (A)

Ozone in ambient air is most often measured with optical methods that directly use how ozone interacts with light. The first common approach is UV photometric analysis, where ozone absorbs ultraviolet light around 254 nm. A UV lamp sends light through a sample, and the detector notes how much light is absorbed. The reduction in light is converted to concentration using Beer-Lambert law, giving a direct, fast, and robust measure of ambient ozone.

The second widespread method is differential optical absorption spectroscopy (DOAS). DOAS analyzes how light across a broad spectrum is absorbed by various species, fitting the ozone-specific absorption features in the UV (and sometimes visible) region while separating them from other absorbers. This can provide path- or point-measured ozone concentrations and is particularly useful for reducing interference and for open-path or multi-axis configurations in field networks.

Other techniques exist, but they’re less common for routine ambient monitoring due to limitations like complexity or cost.