Analysis of PM_2.5 Air Pollution Episode in Early February 2011 over Japan

Abstract

We have analyzed in detail an episode of PM_2.5 from 4 to 7 February 2011 over Japan. The peak time of the PM_2.5 concentration was delayed from west to east along the Sea of Japan on February 4th. High concentrations of PM₁₀ were observed in Korea on February 3rd. A backward trajectory analysis and satellite data showed that the air mass from Mainland China arrived at many sites in Japan. PM_2.5 filter samples were collected at ten sites during the high concentration episode. The chemical composition of PM_2.5 at Miyazaki and Okayama did not change during the episode. On the other hand, the ratio of sulfate, nitrate and ammonium to PM_2.5 had increased in direct proportion to the PM_2.5 concentration during the episode on the east side. The ratio of NO₃^-/SO₄^2- was the lowest for the trans-boundary air pollution. The ratio of NO₃^-/SO₄^2- was higher at the urban site for urban pollution. Based on these results, it was suggested that the high concentrations of PM_2.5 were caused by trans-boundary pollution as well as domestic pollutants in the urban areas.