Transport and Chemical Characteristics of Atmospheric Aerosols at Pengchiayu Island

Abstract
Totally 119 atmospheric aerosol samples were collected at Pengchiayu Island, ca. 55 km north of Taiwan, in the year of 1997 and were analyzed by ICP-OES and ICP-MS for 24 elements, including Al, Fe, Na, Mg, K, Ca, Sr, Ba, Ti, Mn, Co, Ni, Cu, Zn, Mo, Ag, Cd, Sn, Sb, Pb, V, Cr, As, and Se to determine their concentrations.
The result of elemental analyses shows that element levels display a seasonal variability, higher concentrations in spring and winter while lower in summer, which reflects the source regions and relative strengths of atmospheric substances. Crust-originated materials from Asian continent account for the most contributions for the atmospheric element levels at Pengchiayu. The result of enrichment factor calculations indicates three different types of sources, i.e. crustal (Al, Fe, Mn, Ba, Ti and Co), sea salt (Na) and anthropogenic (Pb, Zn, Cd, Mo, Ag, V, Ni, Cr, Cu, Sn, Sb, Se and As) sources, with bi-sources for Mg, Sr and Ca, and tri-sources for K.
The result of wind direction shows that at Pengchiayu the most atmospheric element concentrations carried by north wind are 1.5-2.5 times higher than those by south wind, with notably Mo and As for the northerly, Ni, Sb, Sn and V for the southerly. At least 5 Asian dust episodes have identified at Pengchiayu Island during springtime in 1997 by observing the concurrences of drastically elevated atmospheric Al concentrations and the Fe/Al ratios of 0.5.The result of airflow backward trajectories suggests that element concentrations of the atmosphere are significantly affected by dust transport path. When the airflow is transported mainly over open seas, atmospheric crust- and pollution- derived element levels are low; while passing through China or Taiwan, the levels are raised.Characteristically pollution-derived inter-elemental ratios, such as Pb/Cd, Pb/Sb, Pb/Mo, Pb/Sn and Mn/V ratios, served as tracers help characterize and evaluate the impact of different source regions and relative strengths on aerosol composition.
Corresponding to Asian dust episodes, the Nass/Natotal ratios decrease due to the percentage contributions from crustal-derived Na transported from China. The concentration of Nass is related to both in situ the strength of wind speed and the amount and frequency of precipitation; frequent or bigger precipitation perturbs the well co-variation between Nass concentration and wind speed.
The result of flux calculations demonstrates that spring accounts for 38% of the total atmospheric flux in 1997 and being the most important input to Pengchiayu. Compared with other studies at Pengchiayu during 1996 and 2003, this study of 1997 is a low-dust year. In comparison to fluxes of other oceans, the crustal element flux to Pengchiayu is lower than Yellow sea, NW Mediterranean, Eastern Atlantic margins and North Arabic sea but higher than North Sea and North Pacific; pollutant element lower than NW Mediterranean and the North Sea while higher than Eastern Atlantic margins and the North Pacific.