10:45 AM - 12:15 PM
[HTT17-P07] Understanding transboundary transport processes of PM2.5 in the East China Sea
by Himawari-8 image analysis
Keywords:Himawari-8 image, transboundary transport processes, PM2.5, East China Sea
PM2.5 easily penetrates deep into the lungs, and there are concerns that it may affect the respiratory and circulatory systems. The concentration of PM2.5 in the Asian continent is higher than the average concentration in Japan, and relatively large amounts of pollutants have crossed the border from the Asian continent to Tsushima, Fukuoka, Fukue, and Nagasaki. It has been reported to be susceptible to transboundary pollution from the Asian continent.
The behavior of transboundary pollutants is mainly studied by Aerosol Optical Depth (AOD) observations by Himawari-8 and Tera/Aqua satellites. In the East China Sea surrounded by Jeju Island, the Tsushima Islands, and the Nagasaki Peninsula, which is the subject of our research, the sea is often covered with clouds. The day when AOD can be grasped is very rare. Therefore, in this study, we assumed that PM2.5 in the cloud-covered area moves in the same direction and speed as the clouds, and aimed to investigate the movement of PM2.5 from the trajectory of clouds in satellite images.
First, we obtained Himawari-8 image data created by JAXA's cross-disciplinary product provision system and extracted the East China Sea area from the full disk area. The infrared images at 6.9 μm (band 9) were used to capture the movement of cloud at high altitude clouds, and the images of at 8.6 μm (band 11) were used for the movement of low-altitude clouds.
A method for understanding cloud movement is described. To find the trajectory, we calculated the sum of squared temperature differences between 41 x 41 pixels (80 x 80 km) in an area of 20 pixels on the top, bottom, left, and right of the infrared image at a certain time, and each pixel of the same size in the image after 10 minutes. While moving the area after 15 pixels (30km) vertically and horizontally, the position with the smallest sum was taken as the position after the next 10 minutes.
During the period from October 29, 2019, to February 1, 2022, 41 events in which many transboundary suspended solids movements were observed were analyzed. Observation equipment was installed in Jeju Island, Tsushima, Fukue, Nagasaki University, and Omura, and the increase in PM2.5 concentration was detected at each location to detect different arrival times of PM2.5. is calculated.
We compared the behavior of upper clouds estimated from infrared images (band 9) at 6.9 mm and lower clouds estimated from images (band11) at 8.6 mm. High-speed movement of clouds in the upper layer is estimated to exceed 100 km/h, and in events when the analysis area is dominated by clouds in the upper atmosphere, the direction and speed from measurements on the ground differ greatly. If low-level clouds can be tracked, we were able to obtain results close to those observed on the ground. However, for some events, we got different results. Therefore, we tried to compare the results with the simulation results of the air pollution prediction system VENUS. The movement of the wind presented by VENUS and the behavior of the lower clouds were almost the same. For example, the distribution of transboundary suspended solids on the continent is distributed from the northeast to the southwest, and when moving westward, the concentration increases from the north observation site. If only ground observations were made, it would be assumed that transboundary suspended solids were moving from the north.
Through the combined analysis of ground observation results, Himawari-8 image analysis, and air pollution prediction systems such as VENUS, we were able to understand the transboundary transport process of PM2.5 in the East China Sea, which could not be grasped by satellite observation alone.
The behavior of transboundary pollutants is mainly studied by Aerosol Optical Depth (AOD) observations by Himawari-8 and Tera/Aqua satellites. In the East China Sea surrounded by Jeju Island, the Tsushima Islands, and the Nagasaki Peninsula, which is the subject of our research, the sea is often covered with clouds. The day when AOD can be grasped is very rare. Therefore, in this study, we assumed that PM2.5 in the cloud-covered area moves in the same direction and speed as the clouds, and aimed to investigate the movement of PM2.5 from the trajectory of clouds in satellite images.
First, we obtained Himawari-8 image data created by JAXA's cross-disciplinary product provision system and extracted the East China Sea area from the full disk area. The infrared images at 6.9 μm (band 9) were used to capture the movement of cloud at high altitude clouds, and the images of at 8.6 μm (band 11) were used for the movement of low-altitude clouds.
A method for understanding cloud movement is described. To find the trajectory, we calculated the sum of squared temperature differences between 41 x 41 pixels (80 x 80 km) in an area of 20 pixels on the top, bottom, left, and right of the infrared image at a certain time, and each pixel of the same size in the image after 10 minutes. While moving the area after 15 pixels (30km) vertically and horizontally, the position with the smallest sum was taken as the position after the next 10 minutes.
During the period from October 29, 2019, to February 1, 2022, 41 events in which many transboundary suspended solids movements were observed were analyzed. Observation equipment was installed in Jeju Island, Tsushima, Fukue, Nagasaki University, and Omura, and the increase in PM2.5 concentration was detected at each location to detect different arrival times of PM2.5. is calculated.
We compared the behavior of upper clouds estimated from infrared images (band 9) at 6.9 mm and lower clouds estimated from images (band11) at 8.6 mm. High-speed movement of clouds in the upper layer is estimated to exceed 100 km/h, and in events when the analysis area is dominated by clouds in the upper atmosphere, the direction and speed from measurements on the ground differ greatly. If low-level clouds can be tracked, we were able to obtain results close to those observed on the ground. However, for some events, we got different results. Therefore, we tried to compare the results with the simulation results of the air pollution prediction system VENUS. The movement of the wind presented by VENUS and the behavior of the lower clouds were almost the same. For example, the distribution of transboundary suspended solids on the continent is distributed from the northeast to the southwest, and when moving westward, the concentration increases from the north observation site. If only ground observations were made, it would be assumed that transboundary suspended solids were moving from the north.
Through the combined analysis of ground observation results, Himawari-8 image analysis, and air pollution prediction systems such as VENUS, we were able to understand the transboundary transport process of PM2.5 in the East China Sea, which could not be grasped by satellite observation alone.