Atmospheric dry plus wet deposition and wet-only deposition of dicarboxylic acids
and inorganic compounds in a coastal suburban environment
Ying I. Tsai,Su-Ching Kuo,Li-Hao Young,Li-Ying Hsieh,陳沛悌
Leisure and Recreation Management
Tourism
pchen@chu.edu.tw
Abstract
This study investigated the chemical properties and composition sources of
dicarboxylic organic acids and inorganic salts in dry plus wet deposition (DWD) and
wet-only deposition at a coastal suburban area in southern Taiwan in 2008. DWD is
the accumulation of dry deposition and wet deposition from the beginning of each
new rain event, while wet-only deposition is the wet deposition from the beginning of
each new rain event only. A total of 60 samples were collected during the period of
study. The wet-only deposition samples were slightly more acidic (pH 5.01e5.50) than
the DWD samples (pH 5.51e6.00). The total volume-weighted mean (VWM)
equivalent ionic concentration of 784.3 _ 431.1 meq L_1 in DWD was higher than
that of 682.2 _ 392.4 meq L_1 in wet-only deposition. In both types of deposition the
major cation species were Ca2t, Nat and NHt 4 , and the major anion species were
HCO_3 , Cl_ and non-sea salt (nss) nss-SO2_4 . Total dicarboxylic acids contributed
only 0.60% and 0.45% of the total ionic equivalent concentration in DWD and
wet-only deposition, respectively, and oxalic and malonic acids were the major
dicarboxylic acid species. DWD to wet-only deposition species concentration ratios
(DWD/W ratios) were always higher than 1.0. DWD contained more water-soluble
inorganic salts and dicarboxylic acids than wet-only deposition, with DWD/W ratios
of the dust-bound species Kt, Mg2t and Ca2t as large as 1.6e1.8 and those from
photochemical species nss-SO2_4 and NHt 4 of 1.36 and 1.29, respectively. These
ratios show that the dry deposition flux of dust is greater than that of photochemical
particles. In addition, the 1.81 ratio for oxalic acid shows that oxalic acid is easier to
remove from the atmosphere via dry deposition than malonic and succinic acids.
Probable deposition composition sources for both DWD and wet-only deposition,
investigated using principal component analysis, were marine spray, photochemical
inorganic products, and terrestrial origin and photochemical organic products. As the
study site is close to the coast, marine spray deposits as dry deposition, and the
anthropogenic dicarboxylic acids deposit together with resuspended crustal materials.
Keyword：Rainwater, Dry deposition, Wet deposition, Dicarboxylic acids, Ion
balance, Neutralization