Chemical composition of fog water at four sites in Taiwan

Simon S, Klemm O, El-Madany T, Walk J, Amelung K, Lin P-H, Chang S-C, Engling G, Hsu S-C, Wey T-H, Wang Y-N, Lee Y-C

Abstract

This study characterizes and compares the chemical composition of fog water at four sites in Taiwan. Fog was sampledwith identical active fog collectors (modified Caltech design) using identical sampling strategies at all four sites. While thesites varied largely in terms of altitude above mean sea level (asl), type of fog, and the potential sources of constituents infog water, the chemical composition of fog water was in all cases clearly dominated by H+, NH4+, NO3- and SO42-, makingup more than 85% of the total ion concentrations. The pH ranged from 2.27 to 5.95.Sulfur dioxide emissions from coal combustion in Mainland China and Taiwan as well as nitrogen oxide emissions fromurbanized central-west Taiwan and the greater Taipei region were the main precursors of fog acidity. Ammonia, originating fromagriculture emissions, was the main neutralizer. The Kinmen site (48 m asl), situated on an island close to Mainland China,exhibited the lowest pH and the highest sulfate concentrations. At the Xitou site on the western slopes of the TaiwanCentral Mountain Range (1150 m asl), ammonium from agriculture dominated and lead to relatively high pH. At the sametime, the nitrate/sulfate ratio was highest at this site (> 1 in equivalent units), resulting from relatively large contributionsfrom street traffic. The ion concentrations at the Chilan site (1650 m asl) and the Lulin high mountain site (2862 m asl)were much lower than those at Xitou and Kinmen. While the ion concentrations at Chilan were considerably lower than atLulin, the ion loadings, which is the amount of dissolved ions per volume of air, were similar at Chilan and Lulin.