Abstract
This study characterizes and co
mpares the chemical composition of fog water
at four sites in Taiwan. Fog was sampled
with identical active fog collectors (modified Caltech design) using identical sampling strategies at all four sites. While the
sites varied largely in terms of altitude above mean sea level
(asl), type of fog, and the pot
ential sources of constituents in
fog water, the chemical composition of fog water was in all cases clearly dominated by H
+
, NH
4
+
, NO
3
–
and SO
4
2–
, making
up 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 from
urbanized central-west Taiwan and the greater Taipei region were
the main precursors of fog acidity. Ammonia, originating from
agriculture 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 Taiwan
Central Mountain Range (1150 m asl), ammonium from agriculture dominated and lead to relatively high pH. At the same
time, the nitrate/sulfate ratio was highest at this site (> 1
in equivalent units), resulting from relatively large contributio
ns
from 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 io
n concentrations at Chilan were considerably lower than at
Lulin, the ion loadings, which is the amount of dissolved ions per volume of air, were similar at Chilan and Lulin.
