SEOUL, November 20 (WNM/Yonhap) -- 32 percent of ultrafine dust in South Korea can be attributed to China, reports South Korea’s Yonhap News Agency. However, the annual average concentrations of fine dust pollution have declined at the monitoring sites.

"The self-contributions in China, South Korea and Japan are 91.0 percent, 51.2 percent, and 55.4 percent, respectively. China's contribution to (ultrafine dust in) major cities in Korea is 32.1 percent, and that to major cities in Japan is 24.6 percent," a summary of the joint research study by South Korea, China and Japan posted on the website of South Korea's National Institute of Environmental Research said. This indicates that around 51.2 percent of South Korea's ultrafine dust comes from domestic factors, while 32.1 percent is linked to China.

The findings are part of the Joint Research Project for Long-range Transboundary Air Pollutants in Northeast Asia, a regional project the three countries launched in 1996. The latest report is based on the fourth stage of the study, undertaken between 2013 and 2017.

Researchers studied figures from nine monitoring sites in the three countries: Japan's Rishiri and Oki, China's Dalian, Yantai and Xiamen, and South Korea's Baengnyeong, Ganghwa, Taean and Gosan.

The researchers also noted that the annual average concentrations of air pollutants have declined at the monitoring sites.