Abstract
Abstract. In this study we present the results of an emission study of different phytoplankton samples in aqueous media treated with elevated ozone levels. Halocarbon measurements show that the samples tested released bromoform and different iodocarbons, including iodomethane, iodochloromethane and diiodomethane. Iodide and iodate levels in the liquid phase were representative of concentrations of surface water in a natural environment. Measurement of volatile iodine (I2) emissions from two diatom samples (Mediopyxis helysia and Porosira glacialis) and the background sample (F/2 medium from filtered natural seawater) showed that the quantity of evolved I2 depends on the ozone concentration in the air. This behaviour was assumed to be caused by the oxidation reaction mechanism of iodide with ozone. The I2 emission flux agrees with model calculations at different iodide concentrations. The I2 emission of a natural plankton concentrate sample was, however, very low compared to other samples and showed no dependence on ozone. The reason for this was shown to be the low iodide concentration in the algal suspension, which seems to be the limiting factor in the oxidative formation of I2.
Highlights
Iodine chemistry plays an essential role in the marine boundary layer (MBL) due to its effect on the destruction of tropospheric ozone, perturbation of the HOx–NOx cycle and the formation of new particles and cloud condensation nuclei, thereby leading to changes in the global radiative forcing (Hoffmann et al, 2001; von Glasow and Crutzen, 2003; O’Dowd and Hoffmann, 2005; Bloss et al, 2005; Huang et al, 2010a, b)
Since the formation of I2 and IO is correlated with the iodide concentration (Sakamoto et al, 2009) and the iodide concentration of surface waters is correlated with phytoplankton (Bluhm et al, 2010), this study investigates links between iodide concentrations in microalgae-containing seawater and abiotic formation and emission of I2, utilizing laboratory experiments of the reaction of the seawater surface with ozone
The halocarbon emission rates showed no effect on the different ozone levels; the data for each sample are summarized for high- and low-ozone conditions
Summary
Iodine chemistry plays an essential role in the marine boundary layer (MBL) due to its effect on the destruction of tropospheric ozone, perturbation of the HOx–NOx cycle and the formation of new particles and cloud condensation nuclei, thereby leading to changes in the global radiative forcing (Hoffmann et al, 2001; von Glasow and Crutzen, 2003; O’Dowd and Hoffmann, 2005; Bloss et al, 2005; Huang et al, 2010a, b). Marine species like macroalgae and microalgae play a dominant role in the emission of these compounds (Carpenter et al, 1999; Huang et al, 2013; Saiz-Lopez and Plane, 2004).
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