The U.S. Geological Survey's Hawaiian Volcano Observatory (HVO) determines the amount and composition of gases emitted by Kīlauea Volcano. Changes in gas emissions can reveal important clues about the inner workings of a volcano, so they are measured on a regular basis.
HVO scientists use both remote and direct sampling techniques to measure compositions and emission rates of gas from Kīlauea Volcano.
To determine the rate at which sulfur dioxide (SO2) is emitted, HVO scientists measure the amount of ultraviolet (UV) radiation energy absorbed by the volcanic gas plume as sunlight passes through it. They do this by attaching a mini-UV spectrometer (Flyspec) to a field vehicle and driving beneath the plume.
The amount of carbon dioxide (CO2) emitted by Kīlauea is measured using a small infrared analyzer (LI-COR). Scientists drive this instrument through a gas plume, along with the Flyspec, while it continuously and directly samples the ground-level cross-section of the plume.
Another tool used to measure the relative abundance of some gases, including SO2, CO2, hydrogen chloride (HCl), hydrogen fluoride (HF), carbon monoxide (CO) and water vapor (H20), is the Fourier Transform infrared spectrometer (FTIR), which can continuously sample gas in a volcanic plume. The FTIR measures the amount of light absorbed by gases along an open path between the spectrometer and an infrared source, such as an eruptive vent.