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Observations of I2 at a remote marine site

Lawler, MJ and Mahajan, AS and Saiz-Lopez, A and Saltzman, ES (2014) Observations of I2 at a remote marine site. Atmospheric Chemistry and Physics, 14 (5). pp. 2669-2678.

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Inorganic iodine plays a significant role in the photochemistry of the marine boundary layer, but the sources and cycling of iodine are not well understood. We report the first I2 observations in marine air that is not impacted by coastal macroalgal emissions or sea ice chemistry. The data clearly demonstrate that the very high I2 levels previously reported for coastal air are not representative of open ocean conditions. In this study, gas phase I2 was measured at the Cape Verde Atmospheric Observatory, a semi-remote site in the eastern tropical Atlantic, using atmospheric pressure chemical ionization tandem mass spectrometry. Atmospheric I2 levels typically increased beginning at sunset, leveled off after midnight, and then rapidly decreased at sunrise. There was also a smaller midday maximum in I 2 that was probably caused by a measurement artifact. Ambient I 2 mixing ratios ranged from <0.02-0.6 pmol mol-1 in May 2007 and <0.03-1.67 pmol mol-1 in May 2009. The sea-air flux implied by the nighttime buildup of I2 is too small to explain the observed daytime IO levels at this site. Iodocarbon measurements made in this region previously are also insufficient to explain the observed 1-2 pmol mol-1 of daytime IO. The observations imply the existence of an unknown daytime source of gas phase inorganic iodine. Carpenter et al. (2013) recently proposed that sea surface emissions of HOI are several times larger than the flux of I2. Such a flux could account for both the nighttime I2 and the daytime IO observations.

Item Type: Article
Additional Information: Copyright of this article belongs to European Geosciences Union
Uncontrolled Keywords: atmospheric chemistry; emission; iodine; marine atmosphere; mixing ratio, Atlantic Ocean; Atlantic Ocean (Tropical)
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 23 May 2015 09:01
Last Modified: 23 May 2015 09:04

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