The occurrence frequency and strength of Asian dust storm has been increased in recent years. Under the appropriate meteorological conditions, Asian dust storm could affect Ta iwan’s air quality significantly. This work collected PM10 and PM2.5 at Youngmin mountain for the analyses of mass and chemical compositions. In addition, TSP and PM10 were also collected at Hauwlain site for mass weighing. During the Asian dust (AD) perio ds, the TSP, PM10, and PM2.5 were acquired 41, 69, and 32 effective samples, respectively. In contrast, during non- Asian- dust (NAD) periods, the effective samples of TSP, PM10, and PM2.5 were 14, 25, and 12, respectively. In total, this work collected 193 effective aerosol samples. At Youngming mountain, the PM10 was normally at around 10μg/m3 during NAD periods; however, the PM10 reached as high as 119μg/m3 during AD periods. For PM2.5, the level was at single- digit number for NAD periods, and it could jump up high at 51μg/m3 for AD periods. The TSP was normally below 100μg/m3 at Hauwlian site, while a maximum value of 204μg/m3 was observed during AD periods. Similarly, the PM10 was normally below 80μg/m3 at Hauwlian site, it went up high at 139μg/m3 dur ing AD periods. Evidently, the AD brought a great amount of dusts to Taiwan. For aerosol chemical compositions, the major elements in PM10 and PM2.5 at Youngmin mountain were S and K during NAD periods. During AD periods, the Si, Ca, and Al were cont rasted to be significant. For water- soluble ions, the major ions were sulfate ion, nitrate ion, and ammonium ion both in PM10 and PM2.5 as well as in AD and NAD periods. However, calcium ion was significantly higher during AD periods. The organic carbon was in greater amount than elemental carbon both in PM10 and PM2.5. It was observed that the elemental carbon in PM10 was significantly higher than that in PM2.5 during AD periods. By using HYSPLIT backward air trajectory model (Draxler, 1999), we analyzed aerosol variations collected at Hauwlian site. The results showed that AD influenced the air quality of Hauwlian most significantly. It was followed by poor dispersion of air such as land- sea breeze, re-circulated high- pressure system, and the depression at the lee side of a mountain. The assessment from Science Team indicated that 11 AD events influenced Taiwan’s air quality judged from mesoscale numerical simulation from January to May in 2002. Among them, only two AD events affected Taiwan signific antly and the dates when PSI significantly greater than 100 were only on 9 February and 11 February 2002. For the assessment of AD forecast, a miss on 9 April and an error on 12 April for eight warnings issued in 2002. The results are reasonably good, and the aspect for future forecast is expected to be better.

Asia dust storm, background aerosol, aerosol mass concentration, aerosol chemical compositions, air quality management