Influence Factors on Photochemical Production of Methyl Iodide in Seawater
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Influence Factors on Photochemical Production of Methyl Iodide in Seawater CHEN Yan1), LIU Shanshan1), YANG Guipeng1), 2), 3), and HE Zhen1), 3), * 1) Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education; College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China 2) Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China 3) Institute of Marine Chemistry, Ocean University of China, Qingdao 266100, China (Received January 21, 2020; revised August 12, 2020; accepted September 24, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract Methyl iodide (CH3I) is an important trace greenhouse gas in the atmosphere and an ozone-depleting substance. The influence of different environmental factors, such as the duration of illumination; the strength of illumination; the concentrations of humic acid, ferric ion (Fe3+), and iodide ion (I−); and pH, on the photochemical production of CH3I in artificial seawater (ASW) were tested by simulated solar irradiation. In addition, Yangtze River Estuary waters from inshore to offshore were used to explore the relationship between the photochemical production of CH3I and different sources of dissolved organic matter (DOM) in natural seawater (NSW). The results revealed that higher concentrations of humic acid and I−, as well as higher strengths of illumination and longer illumination durations, promoted the photochemical formation of CH3I in ASW. The addition of Fe3+ accelerated the photochemical production of CH3I, but high concentrations of Fe3+ inhibited the formation of CH3I. Experiments on NSW obtained from the Yangtze River estuary spiked when concentrations of DOM were high, confirming that DOM plays an important role in facilitating the photochemical production of CH3I within the Yangtze River Estuary. The photochemical production of CH3I in the seawater was significantly higher under light conditions relative to dark conditions, indicating that illumination accelerated the production of CH3I. Key words methyl iodide; photochemical production; Yangtze River Estuary; dissolved organic matter
1 Introduction Methyl iodide (CH3I) is an important trace greenhouse gas and environmental pollutant in the atmosphere (Reifenhäuser and Heumann, 1992; Yuan et al., 2016; Carpenter et al., 2017). It can significantly damage the ozone layer and react with other trace gases that indirectly affect the surface temperature of the earth and global climate (Du et al., 2014). The ocean plays an important role in the biogeochemical cycles of CH3I. Sources of CH3I in the ocean are primarily derived from its natural release (Lovelock, 1975; Manley and Dastoor, 1987; Schall et al., 1994; Manley and Cuesta, 1997). The mechanisms of natural CH3I production primarily include marine biotic and abiotic mechanisms (Nightingale et al., 1995). Research on the production of CH3I by marine organisms has been extensive (Gschwend
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