Metal compositions of PM10 and PM2.5 aerosols in Taipei during spring, 2002

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, Ph, 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.