Abstract
Ambient aerosols, collected in Taipei in spring 2002, were measured for concentrations of 15 metals (Al, Ca, Na, Mg, K, Ti, Sr, Ba, Mn, Co, Zn, Pb, Cu, Cd, and Sb). Al was used as a mineral aerosol particle indicator, and based on temporal variations of Al concentration, seven Asian dust storm episodes were identified. The fraction of mineral dust in PM10 was estimated to be around 80% during Asian Dust Storm (ADS) episodes and 15% in non-ADS periods. The metals were categorized into three groups based on their source of origin. The first group consisted of metals from crustal sources, Al, Ca, Sr, Ba, Ti, and Co, the second group was from anthropogenic sources, Pb, Zn, Cd, Cu, and Sb; and the third group was of mixed origins; Na and Mg from sea salt and crustal sources, and K and Mn from crustal and anthropogenic sources. The results of this study demonstrated significant variation in concentrations of metals during spring. Sharp increases in concentration were observed during ADS episodes, particularly for crust-derived elements, Al, Ca, Na, Mg, K, Sr, Ti, Ba, and Co. Metals of anthropogenic origin, Pb, Sb, Cd, and Zn, also increased with ADS episodes, which indicates that significant amounts of pollutant were transported with dust to reach Taiwan. Size-distribution analysis revealed that metals derived from crust and seawater sources (Al, Fe, Sr, Ba, Ti, Na, and Mg) tend to reside in coarse particles, and anthropogenic metals (Pb, Zn, and Cd) in fine particles. Air mass backward trajectory analysis suggested that deserts around Mongolia and the Loess Plateau were the dominant source regions of dust aerosols for ADS. Concentrations of metals in dust were found to change and the wet scavenging affect was strongly indicated.
Highlights
Dust storms (DSs) occur annually in arid/semi-arid deserts of central Asia in spring and late winter
Chester et al suggested that Al could act as an indicator of mineral dust because Al is one of the most common elements found in crustal sources
Temporal variations of Al in PM10 indicate that seven episodes of Asian Dust Storm (ADS) reached northern Taiwan in winter and spring 2002
Summary
Dust storms (DSs) occur annually in arid/semi-arid deserts of central Asia in spring and late winter. Statistics of DSs, for the past 40 years in China, demonstrate a percentage occurrence for March, April and May of about 20%, 58%, and 22%, respectively (Sun et al 2001). The Gobi Desert in Mongolia and Taklamakan Desert in western China, and the Loess Plateau are main source areas of DSs (Liu 1985). Studies have demonstrated that DSs in China were often associated with frontal systems and the Mongolia cyclonic depression (Sun et al 2001). DSs can travel several thousands of kilometers or more from source regions, in the east, to neighboring countries (e.g., Korea and Japan) (Choi et al 2001) and the North Pacific (Duce et al 1980; Gao et al 1992; 1997; Husar et al 2001). Northeastern winter monsoons can bring Asian dust to Taiwan in the lower atmosphere
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