[H-TT19] 環境リモートセンシング

[HTT19-01] 東アジアの越境大気汚染エアロゾルに及ぼす気候変動の影響に関する観測的研究

*蔡 穎¹、入江 仁士¹、Damiani Alessandro¹、板橋 秀一²、竹村 俊彦³ (1.千葉大学、2.電力中央研究所、3. 九州大学応用力学研究所)

キーワード：越境大気汚染、光学的厚さ

Climate change is expected to alter the meteorological field and therefore affect the path of transboundary air pollution in East Asia. Here we propose a new method using an aerosol as a tracer to detect the impact of climate change on the path of transboundary air pollution downwind from China, one of the strongest sources of aerosols. This study focuses on a unique area, which is the downwind from China and over an open ocean with the least impact from human-induced local causes. We analyzed long-term changes of Aerosol Optical Depth (AOD) data (550 nm) observed by Moderate Resolution Imaging Spectroradiometer (MODIS) level-2 atmospheric aerosol product (MOD04_L2 and MYD04_L2), which retrieve from the Dark Target (DT) and Deep Blue (DB) algorithms during 2003 to 2020. We also examined the AOD data (550 nm) of MERRA2 reanalysis data to reduce the effects of data loss due to clouds. For both data, trend analysis and Hovmöller diagram analysis for each latitude-longitude grid were performed, showing expected decreasing trends in AOD over mainland China and Japan in recent years. When we focused on the lower reaches of China’s aerosols, high AOD extending from the coast of China to the northeast region was apparent over the ocean because of the Asian monsoon during this period. The effect of transboundary air pollution almost dominated the AOD over the ocean. Then, to consider the year-to-year change in emissions, we introduced the new quantity, named RAOD , which is a ratio of AOD (ocean) to the value of the coast of China (around 120-125°E). The calculation was made using MODIS and MERRA2 data for each year of 2003-2020. The contribution of sea salt AOD (around 0.05) was removed as a background value. As expected, the result of MODIS is similar to the MERRA2 that RAOD became smaller as farther away from the coastline of China over the ocean. We understand that the RAOD maybe could be assessed from model even observation. Then, we fitted the curve of RAOD with an exponential function and found that the slope did not change year by year significantly. This suggests that the long-term variation in transboundary air pollution patterns was insignificant over year-to-year variations in recent years. In addition, the similarly - calculated RAOD over land with strong local pollutions (Tokyo, Osaka, etc.) likely represent the sum of transboundary pollution and local pollution after considering the dust and volcanic events. In this presentation, a similar analysis is made with data from the Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS), and their comparison results are discussed.