Volcano Watch: Gas math — how we know how much sulfur dioxide volcanoes emit

A spectrometer used in emission rate traverses and how it reads sulfur dioxide emissions. The left diagram shows how incoming UV would get absorbed by the SO2 plume (faded red arrows) along a spectrometer traverse under the plume (yellow arrow). Under clear sky, no UV is absorbed (blue arrows). Inset is a cartoon diagram of a plume “slice” that the spectrometer measures. At right is the telescope of the UV spectrometer mounted to an HVO vehicle during the 2018 lower East Rift Zone eruption. The telescope is aimed up at the sky, and a fiber optic cable (taped to car window) connects the bottom of the telescope to the spectrometer inside the car. Also visible is a wire attached to a GPS antenna on top of the car. (USGS images/Special to West Hawaii Today)

Volcanic gases are an important part of eruptions — they help magma to rise within the earth and erupt, they can tell us how much lava is being erupted, and the volcanic air pollution (vog) they cause can be a hazard. So it is important for the USGS Hawaiian Volcano Observatory (HVO) to measure how much of what kind of gas is being emitted by our volcanoes.