Long-term analysis of AOD separated by aerosol type in East Asia

This study aimed to identify the temporal variations in aerosol loadings and sizes in East Asia based on a method that uses the linear particle depolarization ratio (& delta;P) and coarse-mode fraction of volume concentration (CMFvc) from AERONET Sun/Sky radiometer data. East Asia is the polluted region. Pollution levels continue to increase as a result of population growth and increasing industrialization. The main pollution sources are derived from anthropogenic activities and Asian dust. The data were used to separate the total aerosol optical depths (T) of mixed aerosol plumes into optical depths contributed by dust (zD), coarse-(zPC), and fine-mode pollution (zPF). We used data taken from 1999 to 2021 in East Asia (Beijing, Xianghe on the west, Seoul, Yonsei, Anmyon, and Gwangju in the middle, Osaka and Shirahama in the east, and Taipei in the south). We identified the regional differences; the contribution of zD and zPC to the total T of Chinese sites was almost twice that of other East Asian sites. We analyzed the monthly, seasonal and annual values each of the three aerosol types contributed to total optical depth. The annual variations in zD and zPC from 1999 to 2021 showed a decreasing trend. In contrast, zPF either increased or became stagnant during that time. We conclude that aerosol types in East Asia may have changed. The & ANGS;ngstro & BULL;m exponent of fine-mode particles increased in most regions (0.0008-0.0103 yr  1 for the wavelength range 440-870 nm), which means the mean size of the fine-mode pollution particles tended to decrease, even though & tau;PF increased. The change in particle size might be caused by the decrease in primary emission sources due to the strong air pollution reduction policies in China, Korea, and Japan. Therefore, we need to focus on the change in aerosol properties not just on aerosol loadings.

Automated summary

This study used AERONET Sun/Sky radiometer data to identify the temporal variations in aerosol loadings and sizes in East Asia. The results showed regional differences in aerosol contributions and changes in particle size due to pollution reduction policies. The study highlights the importance of considering aerosol properties, not just aerosol loadings.