In recent years,
several groups have demonstrated the importance of halogen chemistry (mainly Br
and I) in the polar and marine boundary layer. These halogens can impact the
background chemistry of the boundary layer, esp. Ozone and DMS. Furthermore,
S(IV) is oxidized to sulfate by HOCl and HOBr in aqueous particles thereby
providing another link of halogen chemistry with the sulfur cycle. The origins
of the reactive halogen species are different from one another. Bromine and
chlorine are mainly released from sea salt aerosol (marine BL) or sea ice and
snow (polar BL) whereas iodine is derived from organic substances that are
produced in the ocean and photolyze rapidly.
We used the
one-dimensional boundary layer model MISTRA-MPIC with cloud and aerosol
microphysics for detailed process studies of halogen chemistry in the MBL. This
model allows us to study the combined effects of coupled gas and aqueous phase
chemistry (aerosol as well as cloud droplets), vertical transport and cloud
processes. In the discussion of the results I will explain the most important
chemical processes such as acid-catalyzed activation of bromine from sea salt
aerosol, and the potential impact of BrO on the recently measured ``sunrise
ozone destruction''.
Further studies
with MISTRA stress the potential role of halogens for the sulfur cycle in the
remote marine boundary layer and important implications for cloud microphysics
and climate.
Currently we are
examining the potential global influence of halogen chemistry in the marine
boundary layer and the free troposphere. First results from this effort will be
discussed.