Abstract
Abstract. The presence of molecular iodine in the atmosphere is thought to have implications for both climate and human nutritional health, but measurement of the gas at low concentrations requires technically demanding techniques that are not widely accessible. Here, amylose coated denuder tubes and solvent traps coupled with spectrophotometric detection are evaluated and compared as relatively cheap and straightforward methods to measure gaseous molecular iodine at environmentally relevant concentrations. Denuder tubes were found to give unacceptably low and highly variable recoveries of molecular iodine from a test gas source, with values ranging from 1 to 62%. Blank concentrations were also high, being equivalent to a gas phase concentration of 5 pptv under typical operating conditions. Ethanol and hexane solvent traps gave much better performance. Optimisation of the hexane solvent trap method gave 100% recovery and an atmospheric limit of detection of 70 pptv, which is within the range of concentrations observed in the coastal marine atmosphere.
Highlights
Understanding the biogeochemical cycle of iodine is important for three reasons: volatile iodine compounds are photolysed in the atmosphere to give iodine atoms which are implicated in ozone destruction and particle formation reactions and may impact climate (O’Dowd and Hoffmann, 2005); iodine is an essential human nutrient, deficiency of which remains the leading cause of preventable brain damage and mental retardation worldwide (WHO, 2004); the longlived radionuclide iodine-129 is released to the environment
As the blank values quoted here fall within the lower range of atmospheric molecular iodine concentrations (Saiz-Lopez et al, 2006b), the method may only be suitable for measurements where iodine levels are expected to be high and even great care must be taken to minimise contamination
On the basis of the results presented here, it is concluded that amylose coated diffusion denuders are not suitable for the determination of molecular iodine in air
Summary
Understanding the biogeochemical cycle of iodine is important for three reasons: volatile iodine compounds are photolysed in the atmosphere to give iodine atoms which are implicated in ozone destruction and particle formation reactions and may impact climate (O’Dowd and Hoffmann, 2005); iodine is an essential human nutrient, deficiency of which remains the leading cause of preventable brain damage and mental retardation worldwide (WHO, 2004); the longlived radionuclide iodine-129 is released to the environment. It is thought to be either released directly by exposed macroalgae at low tide or formed by the reaction of ozone and iodide on the surface of the algal fronds (Palmer et al, 2005; Kupper et al, 2008; Dixneuf et al, 2009) It may be formed by the reaction of ozone and iodide at the ocean surface (Garland and Curtis, 1981), but as yet no open ocean measurements of atmospheric molecular iodine have been reported. Atmospheric measurements of molecular iodine are made using long path differential optical absorption spectroscopy (LP-DOAS; Saiz-Lopez et al, 2006b) This yields concentrations averaged over a path length of several kilometres so is unsuitable for point measurements and cannot be used on board a ship for open ocean measurements. We evaluate and compare the applicability of starch coated denuders and ethanol and hexane solvent traps for the measurement of molecular iodine at atmospherically relevant concentrations
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