Measurements and modelling of I<sub>2</sub>, IO, OIO, BrO and NO<sub>3</sub> in the mid-latitude marine boundary layer

Abstract

Abstract. Time series observations of molecular iodine (I 2 ), iodine oxides (IO, OIO), bromine oxide (BrO), and the nitrate radical (NO 3 ) 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 2 was detected using the B 3 (0 + u )−X 1 + g electronic transition between 535 and 575 nm. The I 2 mixing ratio was found to vary from below the detection limit (∼5 ppt) up to a nighttime maximum of 93 ppt. Along with I 2 , observations of IO, OIO and NO 3 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 2 and NO 3 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 bromine chemistry model is used to simulate the diurnal behaviour of the BrO radical, demonstrating the importance of halogen recycling through sea-salt aerosol. In the same campaign a zenith sky DOAS was employed to determine the column density variation of NO 3 as a function of solar zenith angle (SZA) during sunrise, from which vertical profiles of NO 3 through the troposphere were obtained. On several occasions a positive gradient of NO 3 was observed over the first 2 km, possibly due to dimethyl sulphide (DMS) removing NO 3 at the ocean surface.

Missing SO<sub>2</sub> oxidant in the coastal atmosphere? – observations from high-resolution measurements of OH and atmospheric sulfur compounds

“…8a and b. This is consistent with previous measurements of IO at Mace Head which showed maximum levels up to 5 pptv (Saiz-Lopez et al, 2006;Alicke et al, 1999). However, other measurements taken over "hot spots" of exposed seaweed beds have shown IO peak values of up to 50 pptv (Commane et al, 2011).…”

Iodine monoxide at a clean marine coastal site: observations of high frequency variations and inhomogeneous distributions

“…1). The research station has been the subject of extensive halogen studies in the past (e.g., Alicke et al, 1999;Saiz-Lopez et al, 2006a) and is described extensively in Heard et al (2006).…”

“…Carpenter et al, 2001;Saiz-Lopez and Plane, 2004;Peters et al, 2005;Saiz-Lopez et al, 2006a;Read et al, 2008;Mahajan et al, 2009;Seitz et al, 2010). Table 1 presents an overview of these spatially-averaged IO observations as well as point measurements of IO at mid-latitude locations.…”

The seaweeds <i>Fucus vesiculosus</i> and <i>Ascophyllum nodosum</i> are significant contributors to coastal iodine emissions

“…In recent years, numerous studies have shown that the coastal particle bursts are closely linked to iodine emission from low-tidal macroalgae exposure (e.g., McFiggans et al, 2004;Sellegri et al, 2005;Saiz-Lopez et al, 2006a;Huang et al, 2010c;McFiggans et al, 2010). A clear negative correlation between IO (the precursor of IOP) and tidal height, and a positive correlation between IO and solar irradiation, have been observed (Carpenter et al, 2001;Saiz-Lopez et al, 2006b;Huang et al, 2010b;Commane et al, 2011). The emission of iodocarbons such as CH 2 I 2 from macroalgae was first proposed to be the source of photolabile iodine (Hoffmann et al, 2001;Carpenter, 2003).…”