Development and Classification of Japanese-Region-Specific Aerosol Models Based on 10-Year Sky Radiometer Observations

To improve remote sensing techniques for global environmental research, aerosol models, indispensable inputs to radiative transfer calculations, should be region specific. Here, we focus on the Japanese region, which is situated downwind of the Asian continent, including China, characterized as one of the most significant sources of aerosols globally. By combining 10-year-long sky-radiometer-retrieved aerosol data from 14 Japanese sites with the k-means++ clustering method, we found that the data were reasonably categorized into four aerosol models: mixed, light-absorbing, oceanic, and oceanic plus urban aerosols. Interestingly, the data were not classified solely as urban aerosols, reflecting that Japan is an island country surrounded by the sea and the air pollution levels were not high. The contribution of the "light-absorbing" category was particularly high at the Fukue site situated in western Japan, as it is close to the Asian continent but isolated from local pollution. Additionally, our results for the Chiba site, which is part of the greater Tokyo megacity located in eastern Japan, indicated that the fraction of the "oceanic" category increased recently, owing to improvements in air quality.