A laboratory study on the uptake of gaseous molecular iodine by clay minerals at different relative humidities. Issue 5 (28th June 2022)

• Record Type: Journal Article
• Authors: Kutsuna, Shuzo; Kaneyasu, Naoki
• Is Part Of: Environmental science. Volume 2:Issue 5(2022)
• Page Start: 1041
• Page End: 1059
• Publication Date: 2022-06-28
• Subjects: 551.5
• DOI: 10.1039/d2ea00039c
• Languages: English
• ISSNs: 2634-3606

Abstract

Abstract : Laboratory experiments on the uptake of I2 by clay minerals support separate estimates of radioiodine dry deposition processes before and after sunrise when I2 is released at night. Abstract : Dry deposition of iodine is a crucial parameter for estimating the public health risk of radioiodine released in the Fukushima Dai-ichi nuclear power plant accident. We measured the uptake of molecular iodine (I2 ) by aqueous solutions and clay minerals in the laboratory to inform estimates of the ground surface resistance for I2 in dry deposition which photolysis limited to nighttime. We injected rectangular pulses of humidified air including I2 into a contactor holding samples of aqueous solutions and clay minerals and monitored I2 concentrations in air leaving the contactor to distinguish I2 loss from I2 adsorption. Uptake of I2 proceeded much more rapidly by aqueous ascorbic acid than by water; the former was limited by mass transfer in the gas-film layer. Uptake of I2 by clay samples was confirmed under dry conditions (20–80% relative humidity), which suggested that it contributed to the dry deposition of I2 onto soils as much as other processes such as reactions with organic matter. The surface resistance for I2 increased with repeated experiments on the same clay samples, reaching 240–670 s m −1, and its dependence on relative humidity differed from that for sulfur dioxide (SO2 ), a commonly used proxy for I2 in scaling methods. Reference values of surface resistance for SO2 above soils remain useful for estimating the resistance for I2 above vegetate surfaces at 80% RH in atmospheric transport and dispersion model calculations but may result in substantial errors at 20% RH unless organic matter in soils contributes to ground surface resistance for I2 .