| 英文摘要 |
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.
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