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2.2. STRATOSPHERIC OZONE 41
2.2.4 Spectroscopic measurements of halogen oxides in the marine boundary
layer in Alcântara/Brazil
Participating scientists Schwärzle, J., A. Lotter, and K. Pfeilsticker
Abstract Since the discovery of stratospheric ozone loss due to these species, the atmospheric
photochemistry of reactive halogen species has become of particular concern. Their fate and behavior
in the atmosphere is still uncertain. During a campaign carried out in Northeastern Brazil, IO was
detected for the first time in a tropical coastal region.
Figure 2.17: Mixing ratio of IO, measured at Alcântara/Brazil. Night time is indicated by grey
background, tidal height is shown in blue in order to point out a possible correlation between tidal
height, daylight and mixing ratios of IO
Background Since reactive halogens have been
detected at different sites all over the world (arctic,
mid-latitudes), the global impact of halogen
oxides on the chemistry of tropospheric ozone is
an arising question. It is of special importance in
the tropics as there is fast vertical convection of
air from the boundary layer into the lower stratosphere.
Funding came through Deutsche Forschungsgemeinschaft
(DFG-PF 384/1-2 and 2-3).
Methods and results The measurements were
conducted by active long-path Differential Optical
Absorption Spectroscopy (DOAS) near the
ocean-surface during a field campaign held in
Alcântara/Northeastern Brazil from December
2004 until January 2005.
Mixing ratios of up to 0.82 ppt of IO were determined
within the IO-absorption-bands in the
spectral range of 418–438 nm. Possible sources of
the inorganic iodine in the marine boundary layer
are the photochemical decay of short-lived organic
iodine emitted from the biologically active oceanic
shelf region (e.g. mangroves), or at lower concentrations
by long-range transport of these species
from the open ocean.
Absorption structures in the range of 320–
350 nm were analyzed for the absorption of
bromine oxide, which could not be detected.
Outlook/Future work
• Identification of iodine source gases
• Abundances of IO in the coastal and continental
tropics
• Determining possible impact of IO on tropospheric/stratospheric
ozone
Main publication Schwärzle, J., Spektroskopische
Messung von Halogenoxiden in
der marinen atmosphrischen Grenzschicht in
Alcântara/Brasilien, Staatsexamensarbeit, University
of Heidelberg, Heidelberg, Germany, 2005.