Measurements of iodine monoxide (IO) above Spitsbergen

Zenith sky measurements of scattered light have been made at Ny-Alesund, Spitsbergen (79 degrees N, 12 degrees E) since the beginning of 1995. A differential optical absorption spectroscopy (DOAS) algorithm has been used to retrieve differential slant column densities (DSCD) of IO for the observations from 1995-1998. IO was detected every year for several days within each month. Model simulations result in an estimated stratospheric IO mixing ratio in the range from 0.65 to 0.80 (+/-0.2) pptv in polar spring 1997. In addition, indications for the presence of tropospheric IO have been found in late spring and summer of each year.