Active long-path differential optical absorption spectroscopy (LP-DOAS) has been an effective toolfor measuring atmospheric trace gases for several decades. However, instruments were large, heavy and powerinefficient,making their application to remote environments extremely challenging. Recent developments infibre-coupling telescope technology and the availability of ultraviolet light emitting diodes (UV-LEDS) havenow allowed us to design and construct a lightweight, portable, low-power LP-DOAS instrument for use at remotelocations and specifically for measuring degassing from active volcanic systems. The LP-DOAS was usedto measure sulfur dioxide (SO2) emissions from La Fossa crater, Vulcano, Italy, where column densities of upto 1.2 1018 molec cm 2 ( 500 ppmm) were detected along open paths of up to 400m in total length. Theinstrument’s SO2 detection limit was determined to be 2 1016 molec cm 2 ( 8 ppmm), thereby making quantitativedetection of even trace amounts of SO2 possible. The instrument is capable of measuring other volcanicvolatile species as well. Though the spectral evaluation of the recorded data showed that chlorine monoxide(ClO) and carbon disulfide (CS2/ were both below the instrument’s detection limits during the experiment, theupper limits for the X/ SO2 ratio (XDClO, CS2/ could be derived, and yielded 2 10 3 and 0.1, respectively.The robust design and versatility of the instrument make it a promising tool for monitoring of volcanic degassingand understanding processes in a range of volcanic systems.
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