Modeling study of the impact of SO₂ volcanic emissions on PM_2.5 pollution in the summer of 2020 in the Kyushu region of Japan

¹ Department of Life and Environment Engineering, The University of Kitakyushu, Kitakyushu, Japan
² Graduate School of Engineering, Division of Sustainable Energy and Environmental Engineering, Osaka University, Suita, Japan
³ National Institute for Environmental Studies, Tsukuba, Japan

^* Corresponding author: uranishi@kitakyu-u.ac.jp

Abstract

Sulfate is a major component of PM_2.5 in Japan, mainly produced from sulfur dioxide (SO₂) oxidations. Volcanic activity is a significant source of SO₂ alongside anthropogenic activities (fossil fuel combustion). This study focused on the PM_2.5 pollution episode in the Kyushu region triggered by the Nishinoshima volcanic eruption in the summer of 2020. To simulate the episode, the CMAQ model was employed, incorporating a volcanic SO₂ emission inventory (VolcCarn v202302). Three sensitivity simulations were conducted to assess the impact of SO₂ injection height on PM_2.5 concentrations. Although the WRF model accurately simulated meteorological conditions, the CMAQ model exhibited difficulty in matching observed PM_2.5 levels in Fukuoka and Kagoshima in the higher SO₂ injection cases (Case I and II), with the exception of the lowest injection height scenario (Case III) that closely matched observed PM_2.5 concentrations. Furthermore, Case III indicated that the contribution of volcanic sources to PM_2.5 concentrations in Fukuoka and Kagoshima was considerable, with over 90% of PM_2.5 on peak days attributed to these sources. The study indicated that the Nishinoshima eruption was one of the primary contributors to the PM_2.5 pollution episode in Kyushu and that the injection height had a significant impact on the model performance.