Engineers at NASA Goddard Space Flight Center tasked with measuring atmospheric ozone — an important pollutant and greenhouse gas — discovered that existing optical instrumentation would not be sufficient to achieve their performance requirements. Specifically, the current systems did not possess the precision necessary to make low-concentration measurements at fast time resolution.
They developed a technique that utilizes Cavity Enhanced Absorption Spectroscopy (CEAS) with a simple and inexpensive optical and electrical design to overcome these limitations and achieve high-quality ozone measurements. The sensitivity of the instrument developed using CEAS exceeds that of commercially available instrumentation and matches performance of complex chemiluminescence instruments.
The technique takes advantage of ozone’s strong absorption at specific wavelengths in the ultraviolet (UV). To take measurements, UV light is projected through a cell bounded by highly reflective mirrors. These mirrors increase the path length of the cell by inducing the light to bounce back and forth within the cell, increasing the likelihood of ozone absorption within the cell. Finally, an absorption measurement is taken via a detector outside the cell and opposite of the UV source.
This innovation produces an ozone detection precision of 0.12 parts per billion (ppb) in 0.1-second integration. This corresponds to 0.012 ppb in ten seconds integration.