Increases of wet deposition at remote sites in Japan from 1991 to 2009

Abstract

Temporal trends in wet deposition of major ions were explored at nationwide remote sites in Japan from April 1991 to March 2009 by using the seasonal Kendall slope estimator and the nonparametric seasonal Kendall test. For the trend analysis, datasets from eight remote sites (Rishiri, Echizenmisaki, Oki, Ogasawara, Shionomisaki, Goto, Yakushima, and Amami) were selected from the Japanese Acid Deposition Survey (JADS) conducted by the Ministry of the Environment. Deposition of H+ has been increasing at remote sites in Japan on a national scale. Significant (p ≤ 0.05) increases in H+ deposition were detected with changes of +3–+9 % year−1 at seven sites, while insignificant increases were observed at one site. Depositions of non-sea salt (nss)-SO 4 2− and NO 3 − significantly increased at four and six sites, respectively, with changes of +1–+3 % year−1. Significant increases in precipitation at four sites would have contributed to the increase in depositions of H+, nss-SO 4 2− , and NO 3 − . The emission trends of SO2 and NOx did not corresponded to the deposition trends of nss-SO 4 2− and NO 3 − . The different trends indicated that temporal variation of precipitation amount trend dominated the deposition trends.