Relationship between wet deposition of sulfate and nitrate and rainfall amount in Japan

Abstract

A regression model of wet deposition on rainfall amount for non-seasalt sulfate (nss-SO₄ ²⁻) and nitrate (NO₃ ⁻) was applied to a data set obtained through a nationwide survey from April 1989 to March 1993. Wet-only samples on a biweekly basis were collected at 29 sites over Japan. Reparameterized bivariate lognormal distribution was employed to describe the joint distribution of concentration (C) and rainfall amount (R) for each site. Ranges of geometric mean (μ_D) of biweekly deposition (D = C. R) for each site were 0.54–2.90 meq m⁻² for nss-SU₄ ²⁻, and 0.21–1.36 meq m⁻²2 for NO₃ ⁻; that of biweekly rainfall amount (μ_R) was 24.1–78.0 mm. Urban or industrialized areas had high values of μ_D for these ions. Ranges of estimates of the slope of the regression equation of log(D/μ_D) on log(R/μ_R), were 0.45–0.99 for nss-SO₄ ²⁻, and 0.35–0.86 for NO₃ ⁻; thus estimates of the slope for nss-SO₄ ²⁻ tend to be larger than those for NO₃ ⁻. The present analysis, consequently, statistically clarified some differences between the two ions in deposition processes which is understood in the light of current knowledge of atmospheric chemistry.