Abstract
Abstract. A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved if an additional sea-air flux of inorganic iodine (e.g., I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.
Highlights
M lower part of the marine boundary layer
The TransBrom expedition was conducted aboard the German research vessel (R/V) Sonne departing in Tomakomai, Japan (42◦ N, 141◦ E) on 9 October 2009 and arriving at Townsville, Australia (19◦ S, 146◦ E) on 24 October 2009
The present paper reports on a latitudinal cross-section of surface iodine monoxide (IO) mixing ratios and IO profiles, which were taken in the marine boundary layer (MBL) of the Western Pacific (42◦ N, 141◦ E to 19◦ S, 146◦ E)
Summary
The TransBrom expedition was conducted aboard the German research vessel (R/V) Sonne departing in Tomakomai, Japan (42◦ N, 141◦ E) on 9 October 2009 and arriving at Townsville, Australia (19◦ S, 146◦ E) on 24 October 2009 (cruise length of 7500 km). On October 2009 clear skies provided the best viewing condition during the whole cruise. Major objectives of the TransBrom Sonne cruise were the investigation of the halocarbon concentrations in the surface seawater and air, and the estimation of their seaair source strengths and sinks. This appears to be relevant since the Western Pacific is regarded as the main “entrance gate” for naturally emitted halocarbons entering the stratosphere (Bonazzola and Haynes, 2004; Kruger et al, 2008; Fueglistaler et al, 2009). The IUP Bremen group focussed on the measurements of NO2 and HCHO and their validation with satellite measurements (Peters et al, 2012) and the IUP Heidelberg group focussed on the retrieval of IO mixing ratios and profiles in the MBL along the cruise track (this study)
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