Halogen Oxide Studies in the Boundary Layer by Multi Axis Differential Optical Absorption Spectroscopy and Active Longpath-DOAS

Abstract

The importance of reactive halogen species (particularly halogen oxides) in the troposphere is due to their strong effect on tropospheric ozone levels, which has been first discovered during surface ozone depletion episodes in the polar boundary layer after polar sunrise (bromine oxide, BrO). Halogen oxides have also been reported from mid-latitude coastal sites (iodine oxide, IO and iodine dioxide, OIO) and from the Dead Sea basin (BrO). Results from the field studies performed in framework of this thesis at Arctic and mid- latitude locations are presented here. BrO and its vertical profile near the ground has been observed during surface ozone destruction in the Canadian high and low Arctic. First simultaneous measurements of BrO and IO in the Arctic boundary layer were performed by ground-based MAX-DOAS, which was developed within this work. The measurements at the Hudson Bay represent the southernmost and first direct observations of Arctic surface ozone losses due to BrO and allowed for the first time to study the day and nighttime chemistry of BrO at high time resolution. Molecular bromine was inferred to be a major reservoir compound during the night, initiating sunrise ozone destruction upon photolysis. The first simultaneous measurements of BrO and gas phase elemental mercury at high time resolution in the Canadian Arctic support the proposed key role of BrO as oxidant for mercury in the gas phase during polar springtime. Further measurements of halogen oxides at clean and moderately polluted mid-latitude coastal sites yielded new field data on halogen oxide concentrations and upper limits at different pollution levels.