Dr Katja Seitz
University of Heidelberg, GERMANY
Topic: Modelling DOAS measurements of reactive halogen species (Report)
Host: Roland von Glasow, School of Environmental Sciences, University of East Anglia, Norwich, UK.
Date of STSM: 05/10/2009 to 24/10/2009
STSM code: 4676
In the framework of her PhD thesis, Dr Seitz performed field measurements of reactive halogen
species at Mace Head and Mweenish Bay at the Irish West Coast. The measurements were
made using Long-Path Differential Optical Absorption Spectroscopy (DOAS). At Mace Head
the reactive halogen species IO, I2 and BrO could be detected, whereas at Mweenish Bay only
IO and BrO could be identified. At Mace Head it was possible to compare our path-averaged
results to in-situ techniques: For IO a comparison with laser-induced fluorescence (LIF) was
performed and I2 was compared to a denuder technique and broad band cavity enhanced
absorption spectroscopy (BB-CEAS). At Mweenish Bay two light paths with different lengths
were established to obtain information about the spatial distribution of the trace gases of
interest and also measurements of ultrafine particles were performed. The results of both
measurement sites support the so-called “hot-spot-theory” according to which the reactive
iodine species have to be inhomogeneously distributed to explain the observed particle
formation. However, to get a better understanding of the spatial distribution of the trace gases
and the mechanisms that lead to the formation of new particles, it is necessary to implement
the data in a model.
The aim of this STSM is to implement the experimental results in the
model MISTRA to obtain a better understanding of the related processes and also to be able to
make global estimates for both emission of reactive halogen species and particle formation in
coastal environments. Since the reactive halogen species are involved in several atmospheric
processes and particle formation can affect local climate, these tasks are of great relevance.