Aerosol characterization at Taiwan's northern tip during Ace-Asia

Abstract

In collaboration with major Pacific Rim countries monitoring transported yellow dust (YD) from East Asia [Aerosol Characterization Experiment in Asia (ACE-Asia)], we made measurements of PM2.5 and PM10 at the Shi-Men site located on Taiwan's northern tip from March to May 2001. Herein we report the results from those measurements. The average mass concentrations of PM10 were 133, 103, and 49 μgm-3 for April YD, May YD, and non-YD periods, respectively. In contrast, PM2.5 averages for April YD, May YD, and non-YD periods were 41, 49, and 25 μgm-3, respectively. From the comparisons of particulate matter (PM) mass concentration between YD and non-YD periods, we find an enhancement of 110 and 171% in PM10 and 64 and 96% in PM2.5 for the two YD events. The enhancement of water-soluble ions is greater in absolute mass concentration but is significantly less in mass fraction. Since major ions like NO3-, NH4+ and SO42- are primarily from anthropogenic sources, their enhancements indicate a significant long-range transport of air pollutants from the Asian Continent to the site. Ions like Na+, Cl-, Ca2+, and NO3- are pre dominantly distributed in coarse fraction. In contrast, the NH4+ and SO42- are preferentially distributed in fine fraction. Aerosol carbon is enhanced in mass concentration but not in mass fraction for YD samples, and the ratios of OC/EC for both PM10 and PM2.5 in each YD sample are similar and almost unvaried with PM concentration. By examining aerosol elemental content, we find that elements such, as Fe, Ti, Si, Ca, K, and Al, are enhanced in YD samples. A method of reconstructed mass shows the resolved mass fractions in PM10 for April average, May average, and non-YD average account for 63, 69, and 72%, respectively and those for PM2.5 are 83, 94, and 91%, respectively. The NOAA HYSPLIT back-trajectory model shows that April YD airflow came from the Gobi Desert in China via a relatively un-polluted inland route, while the May YD airflow transported along the industrial coastal areas in China. This difference in the transport path between April and May dust events may account for the difference in their aerosol compositions.