Atmos. Chem. Phys. Discuss., 5, 9731-9767, 2005
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Measurements and modelling of I2, IO, OIO, BrO and NO3 in the mid-latitude marine boundary layer
A. Saiz-Lopez1, J. A. Shillito2, H. Coe2, and J. M. C. Plane1
1School of Environmental Sciences, University of East Anglia, Norwich, UK
2School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK

Abstract. Time series observations of molecular iodine (I2), iodine oxides (IO, OIO), bromine oxide (BrO), and the nitrate radical (NO3) 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 was detected using the B3Π(0+u)−X1Σxg electronic transition between 535 and 575 nm. The I2 mixing ratio was found to vary from below the detection limit (~5 ppt) up to a nighttime maximum of 93 ppt. Along with I2, observations of IO, OIO and NO3 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 I2 and NO3 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 NO3 as a function of solar zenith angle (SZA) during sunrise, from which vertical profiles of NO3 through the troposphere were obtained. On several occasions a positive gradient of NO3 was observed over the first 2 km, possibly due to dimethyl sulphide (DMS) removing NO3 at the ocean surface.

Citation: Saiz-Lopez, A., Shillito, J. A., Coe, H., and Plane, J. M. C.: Measurements and modelling of I2, IO, OIO, BrO and NO3 in the mid-latitude marine boundary layer, Atmos. Chem. Phys. Discuss., 5, 9731-9767, doi:10.5194/acpd-5-9731-2005, 2005.
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