Which ozone measurement method relies on ultraviolet light absorption?

• A. Chemiluminescence
• B. DOAS
• C. UV photometric ozone analyzer (UV absorption)
• D. Infrared spectroscopy

Answer: (C)

Ozone is measured by how much ultraviolet light it absorbs. Ozone strongly absorbs UV light around 254 nm, so a UV photometric ozone analyzer shines UV light through a sample and detects how much makes it through. The more ozone present, the less light reaches the detector. By applying the Beer-Lambert relationship, the instrument converts the amount of absorbed light into an ozone concentration. This direct UV-absorption approach is fast and widely used for ambient ozone monitoring because it relies on a specific UV absorption feature of ozone.

Other methods use different principles: chemiluminescence measures light emitted from a chemical reaction involving ozone, not UV absorption; DOAS uses absorption across multiple wavelengths (in the UV or visible) to quantify gases; infrared spectroscopy detects absorption bands in the infrared.