[A-AS09] Atmospheric Chemistry

[AAS09-18] Long-term observations of planetary-boundary-layer mean sulfur dioxide concentrations by MAX-DOAS in Japan, including the COVID-19 pandemic period

*Kometani Sota¹, Hitoshi Irie¹, Alessandro Damiani² (1.Center for Environmental Remote Sensing Chiba University, 2.NIES/CCCA)

Keywords:SO2, MAX-DOAS, planetary-boundary-layer, COVID-19 pandemic period

We conducted long-term observations of planetary-boundary-layer (PBL) mean sulfur dioxide (SO₂) concentrations by ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) utilizing the ultraviolet region. The observations were made at five sites in Japan, namely Sendai, Tsukuba, Chiba, Kasuga, and Fukue, which have different geographical features. At Chiba, four MAX-DOAS instruments were operated simultaneously with four different viewing directions (i.e., north, east, west, and south). The longest record of 11 years was obtained at Tsukuba. For Kasuga and Fukue located in western Japan, the back trajectory analyses indicated that the influence of volcanic eruptions occasionally increased, the daily PBL SO₂ concentrations to 10 times that of the median over the entire observation period. In contrast, the high concentrations at Chiba, Tsukuba, and Sendai located in eastern Japan indicated the influence of power plants and factories around the ports and coastal areas. At these urban and suburban sites, the highest SO₂ concentrations were less than 10 times the median value during the observation period. This suggests that volcanic eruptions have a greater impact on the daily mean SO₂ concentrations in Japan than anthropogenic sources in recent years. In addition, an interesting abrupt reduction in PBL SO₂ concentrations by 59%, was detected. This reduction was likely caused by 1) the shutdown of a major thermal power plant (Anegasaki) and 2) the aging and reduced operation of a major steel mill (Kimitsu) due to the reduced demand for iron during the COVID-19 pandemic period. Analysis of wind direction and speed at the Chiba site after 2022 showed that SO₂ concentration tends to be higher when winds blow from the southwest, suggesting the influence of thermal power plants located in the southwest direction of the Chiba site and ships on Tokyo Bay. In this presentation, we will also present the results of a study on SO₂ concentration variations by estimating SO₂ concentrations in the COVID-19 pandemic period from the data before the COVID-19 pandemic period using machine learning and comparing them with the actual observations.