Volcanic Cloud from Iceland's Bardarbunga Measured by Ozonesonde at Summit, Greenland

Chance Sterling (1,2), Bryan Johnson (2), Irina Petropavlovskikh (1,2), Patrick Cullis (1,2), Emrys Hall (1,2), Allen Jordan(1,2)

Abstract
We present here a unique measurement of an SO2 plume at the Summit, Greenland station from the Icelandic volcano Bardarbunga over 1200 km away. We also highlight the potential value of ozonesonde soundings for satellite validation of SO2 plume height. Ozonesondes and specifically electrochemical concentration cells (ECC) have been used by NOAA for 30+ years to measure and monitor stratospheric ozone. The measurement principle is well-known and based on the iodometric method, the fast reaction of ozone (O3) and iodide (I-) in an aqueous 1% potassium iodide solution. However, the aqueous sulfur dioxide (SO2) oxidation reaction also occurs in the ECC. The oxidation of SO2 produces two electrons in the cathode cell canceling out the two electrons consumed by the normal O3/I- reaction. Therefore, when SO2 is present in the atmosphere, one reacted SO2 molecule cancels out one reacted O3 molecule, compromising the ozone measurement. However, valuable information can be obtained about tropospheric SO2. During volcanic off-gassing events, SO2 concentrations often become greater than O3 concentrations. In this scenario, the entire ozone signal is lost. If all other data suggests the instrument is operating properly, it can be inferred that the ozonesonde passed through SO2 rich air. The real value of the inferred SO2 measurement is in the vertical resolution which for the current i-Met/ozonesonde package used at NOAA is 1 second data or approximately 5 meters.