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Temperature, humidity, and ionisation effect of iodine oxoacid nucleation.

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He, Xu-Cheng 
Shen, Jiali 
Baalbaki, Rima 
Dada, Lubna 


Iodine oxoacids are recognised for their significant contribution to the formation of new particles in marine and polar atmospheres. Nevertheless, to incorporate the iodine oxoacid nucleation mechanism into global simulations, it is essential to comprehend how this mechanism varies under various atmospheric conditions. In this study, we combined measurements from the CLOUD (Cosmic Leaving OUtdoor Droplets) chamber at CERN and simulations with a kinetic model to investigate the impact of temperature, ionisation, and humidity on iodine oxoacid nucleation. Our findings reveal that ion-induced particle formation rates remain largely unaffected by changes in temperature. However, neutral particle formation rates experience a significant increase when the temperature drops from +10 °C to -10 °C. Running the kinetic model with varying ionisation rates demonstrates that the particle formation rate only increases with a higher ionisation rate when the iodic acid concentration exceeds 1.5 × 107 cm-3, a concentration rarely reached in pristine marine atmospheres. Consequently, our simulations suggest that, despite higher ionisation rates, the charged cluster nucleation pathway of iodic acid is unlikely to be enhanced in the upper troposphere by higher ionisation rates. Instead, the neutral nucleation channel is likely to be the dominant channel in that region. Notably, the iodine oxoacid nucleation mechanism remains unaffected by changes in relative humidity from 2% to 80%. However, under unrealistically dry conditions (below 0.008% RH at +10 °C), iodine oxides (I2O4 and I2O5) significantly enhance formation rates. Therefore, we conclude that iodine oxoacid nucleation is the dominant nucleation mechanism for iodine nucleation in the marine and polar boundary layer atmosphere.



37 Earth Sciences, 3701 Atmospheric Sciences, 51 Physical Sciences

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Environ Sci Atmos

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Royal Society of Chemistry (RSC)
Vienna Science and Technology Fund (VRG22-003)
Alfred Kordelinin Säätiö (220257)
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (200020_172602, 200021_169090, 200021_213071, 206021_198140, 20FI20_172622)
HORIZON EUROPE Marie Sklodowska-Curie Actions (764991)
Strategic Research Council (352431)
European Research Council (742206)
Bundesministerium für Bildung und Forschung (01LK1601A, 01LK1601C, 01LK2201A, 01LK2201B)
Jane ja Aatos Erkon Säätiö (Quantifying carbon sink, CarbonSink+ and their int)
Jenny ja Antti Wihurin Rahasto (Gigacity)
National Natural Science Foundation of China (42175118)
Research Council of Finland (337549, 337552, 302958, 1359331, 349659, 1325656, 311932, 334792, 316114, 325647, 325681, 347782)
National Science Foundation (AGS-1801280, AGS-2215522, AGS-2027252, AGS-2215489, AGS-2132089, AGS-1602086, AGS-1801329, AGS-2215527)