Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
1680-7367
1680-7375
5
5
2005
10.5194/acpd-5-9731-2005
http://www.atmos-chem-phys-discuss.net/5/9731/2005/
http://www.atmos-chem-phys-discuss.net/5/9731/2005/acpd-5-9731-2005.html
http://www.atmos-chem-phys-discuss.net/5/9731/2005/acpd-5-9731-2005.pdf
9731
9767
2005-10-10
Measurements and modelling of I<sub>2</sub>, IO, OIO, BrO and NO<sub>3</sub> in the mid-latitude marine boundary layer
A. Saiz-Lopez
J. A. Shillito
H. Coe
J. M. C. Plane
School of Environmental Sciences, University of East Anglia, Norwich, UK
School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
Time series observations of molecular iodine (I<sub>2</sub>), iodine
oxides (IO, OIO), bromine oxide (BrO), and the nitrate radical
(NO<sub>3</sub>) in the mid-latitude coastal marine boundary layer
(MBL) are reported. Measurements were made using a new long-path
DOAS instrument during a summertime campaign at Mace Head on the
west coast of Ireland. I<sub<2</sub> was detected using the
<i>B</i><sup>3</sup>Π(0<sup>+</sup><sub>u</sub>)−<i>X</i><sup>1</sup>Σ<sup>x</sup><sub>g</sub> electronic transition
between 535 and 575 nm. The I<sub>2</sub> mixing ratio was found to
vary from below the detection limit (~5 ppt) up to a nighttime
maximum of 93 ppt. Along with I<sub>2</sub>, observations of IO, OIO
and NO<sub>3</sub> were also made during the night. Surprisingly, IO
and OIO were detected at mixing ratios up to 2.5 and 10.8 ppt,
respectively. A model is employed to show that the reaction
between I<sub>2</sub> and NO<sub>3</sub> is the likely nighttime source of
these radicals. The BrO mixing ratio varied from below the
detection limit at night (~1 ppt) to a maximum of 6 ppt in the
first hours after sunrise. A model shows that this diurnal
behaviour can be explained by halogen recyling in sea-salt aerosol
building up photolabile precursors of atomic Br during the preceding
night. In the same campaign a zenith sky DOAS was employed to
determine the column density variation of NO<sub>3</sub> as a function
of solar zenith angle (SZA) during sunrise, from which vertical
profiles of NO<sub>3</sub> through the troposphere were obtained. On
several occasions a positive gradient of NO<sub>3</sub> was observed
over the first 2 km, possibly due to dimethyl sulphide (DMS)
removing NO<sub>3</sub> at the ocean surface.