Chemical Features and Depositions of Ionic Species Associated with Dew and Frost in Western Niigata-City

Abstract

From April 2001 to April 2002, a total of 102 dew and 9 frost samples were collected using a Teflon sheet at a rural site in western Niigata-City, in the costal area along the Sea of Japan. Dry deposition to the dry Teflon sheet, fog and/or drizzle to the Teflon sheet, and atmospheric deposition using filtrating bulk samples were also collected for a comparison of ionic composition and flux measurement. The volume weighed mean pHs of dew, frost and fog (and/or drizzle) were 5.9, 5.8 and 3.7, respectively; whereas it was 4.7 for atmospheric deposition. The total water flux from dew and frost per year was 15.0 mm, correspondsing to nearly 1% of precipitation. In the following series of ions, the number in parentheses gives the percent of the yearly flux of the ion in dew and frost compared to atmospheric deposition for the same period: H⁺ (0.1), NH₄⁺ (5.8), Na⁺ (0.7), K⁺ (2.6), nss-Ca²⁺ (2.9), Mg²⁺ (0.8), nss-SO₄²⁺ (1.5), NO₃^- (1.8), Cl^- (0.7). The mean concentrations of NH₄⁺, K⁺ and organic acid (HCOOH and CH₃000H) in dew were higher than those in frost; whereas sea-salt components were higher in frost. Depositions accompanied by dew and frost were strongly affected by dry deposition, however, there were large differences between dew and dry deposition of H⁺, HCOOH and NO₂^-. Accordingly, HCOOH and NO₂^-are important ion species for the acidification of dew.