What does the acronym DOAS stand for in ozone measurement?

• A. Dynamic Optical Absorption Spectrometry
• B. Differential Optical Absorption Spectroscopy
• C. Differential Optical Aerial Spectrometry
• D. Direct Optical Absorption Spectroscopy

Answer: (B)

DOAS stands for Differential Optical Absorption Spectroscopy. The idea is to detect ozone by looking at how its molecules absorb light at specific wavelengths and separating those narrow, gas-specific absorption features from the broad, slowly varying losses caused by scattering and instrument response. In practice, a light path through the air is measured with a spectrometer, and the spectrum is analyzed to isolate the differential absorption features of ozone using reference absorption spectra. This approach lets us quantify the amount of ozone along the light path (the slant column) and works well because it focuses on the distinctive, wavelength-specific fingerprints of ozone while canceling out other broad effects.