In order to investigate the long-term trend of baseline level air pollution in Hokkaido, particulate matter observations were carried out in Ochi-ishi, Nemuro City, and Rishiri, Hokkaido, Japan, from 1997 to 2018. Overall, there was a decreasing trend in inorganic elements and sulfate ion, which are thought to be mainly derived from anthropogenic sources, after 2009. This coincided with the decreasing trend of PM and other air pollutant emissions in China, which peaked in 2011. On the other hand, no clear long-term trend was observed for nitrate. In addition to the relatively small decreasing NOx emissions in China, there is the possibility that biomass combustion in Siberia or other regions may have contributed to this. Seasonal changes in the SPM were particularly high in March, April, October and November. Al, Fe, which are components in soil, and As were high in March to April and November, and Cd, Sb and Pb, which are considered to be the mainly derived from anthropogenic pollution, were especially high in November, March and April. The concentrations were generally higher in Rishiri Island than in Ochi-ishi, suggesting that the influence of anthropogenic sources in the western continent was strong. On the other hand, the concentrations of methanesulfonic acid (MSA), which is considered to be of biological origin, and V, considered to be of marine origin, increased in the summer mainly from June to July, and this tendency was significant in Ochi-ishi.