Hydroxyl Radical (OH) Gas Detector

The OH Gas Detector combines the properties of Gas Correlation Radiometry (GCR) with Broad Band Cavity Enhanced Absorption Spectroscopy (BBCEAS) to measure the absorption of OH remotely. GCR utilizes a precise filter with a high spectral resolution that is matched to the absorption features of a specific gas. BBCEAS measures light intensity through a stable optical cavity. OH gas absorbs strongly at specific wavelengths in ultraviolet light. Using the sun as a light source, modulated sunlight is split into two, independent gas cells. One gas cell contains a vacuum and the other gas cell contains OH gas. The OH Gas Detector uses the gas cell containing OH gas as a precise bandpass filter for GCR. Due to the short lifespan and reactivity of OH gas, OH gas must be actively generated to use as a reference and only a limited amount can be generated. BBCEAS is used to increase the path length within the gas cell for a measurement to be possible using the small amount of OH gas present within the gas cell. The OH Gas Detector measures the absorption rate of each gas cell, which is ratioed to determine the remote level of OH absorption. Hydroxyl radical (OH) is a greenhouse gas that is highly reactive. It reacts with many atmospheric pollutants, including itself, and is considered an important part of eliminating greenhouse gases, especially methane and ozone. OH gas plays a major role in the concentrations of greenhouse gases and is the most prevalent oxidizer in the troposphere, the lowest layer of the Earth’s atmosphere. Due of its high reactivity, OH gas is short-lived (a lifetime of less than one second) and thus, difficult to measure. The OH Gas Detector can measure the absorption of OH gas for detection purposes.