Higher than normal levels of toxic smog spreading to Japan from China were observed at 48 of 155 observatories nationwide, or 31 percent of the total, on Jan. 31, the National Institute for Environmental Studies said.

The 48 observatories with higher levels of so-called PM2.5, hazardous particulate matter smaller in diameter than 2.5 microns, are located in 12 prefectures, mostly in western Japan, including Aichi, Osaka and Hiroshima.