[M-AG33] Basic study on the estimation of the "Black Rain" area caused by the atomic bomb

[MAG33-P09] Characterization of new particle formation process in the Noto Peninsula based on ultrafine particle and air ion measurements

*Masaki Komatsu¹, Seiji Kubota², Hiroyuki Hyono², Yoko Iwamoto³, Alessia Nicosia⁴, Ayumi Iwata⁵, Shungo Kato⁶, Yasuhiro Sadanaga⁷, Naoki Kaneyasu^8,9, Atsushi Matsuki¹⁰ (1.School of Geosciences and Civil Engineering, Kanazawa University, 2.Graduate School of Natural Science and Technology, Kanazawa University, 3.Graduate School of Integrated Sciences for Life, Hiroshima University, 4.Institute of Atmospheric Sciences and Climate (CNR-ISAC), 5.Department pf Physical Meteorology Research Meteorological Research Institute, Japan Meteorological Agency, 6.Department of Applied Chemistry for Environment, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, 7.Graduate School of Engineering, Osaka Metropolitan University, 8.Fukushima Institute for Research, Education and Innovation, 9.National Institute of Advanced Industrial Science and Technology, 10.Institute of Nature and Environmental Technology, Kanazawa University)

Keywords:New Particle Formation, Cluster ions, Ion-induced nucleation, Ambient dose rate

The particles generated by new particle formation (NPF) ultimately determine the concentration of cloud condensation nuclei (CCN), thereby influence the Earth's climate. The mechanism of NPF is largely driven by regional environmental factors, and its detailed understanding requires the direct observation of ultrafine particles as well as air ions. In this study, we newly introduced NAIS (Neutral cluster and Air Ion Spectrometer, Airel, Estonia) to observe the size distribution of newly formed particles and air ions at NOTOGRO (Noto ground-based Research Observatory: 37.45N, 137.36E), along the western-coast of mainland Japan. We identified in total 46 NPF events during the observation period from 18 May 2023 to 30 November 2023. Most events were predominantly daytime events most likely involving photochemical oxidation. The highest event frequency occurred in May when solar radiation and associated H₂SO₄ proxy were the highest. Throughout the observation period, NPF events were accompanied by an increase in ion concentrations. However, the contribution of ions to daytime NPF in Noto was found to be minimal, suggesting that the neutral clustering being the dominant pathway. It must be noted that few nighttime NPF events were also observed in Noto in late autumn. However, the nighttime events observed in this study did not involve in-situ formation and growth of ultrafine and ions, suggesting transport of previously formed particles from upwind. Our findings suggested the possibility of ion-induced nucleation occurring over the Sea of Japan accompanied by the inflow of clean air masses from the free troposphere after the passage of a cold front.