亚洲沙尘影响台湾期间大气悬浮微粒之粒径大小及化学组成变化趋势

Variation of Size Distribution and Chemical Composition of Atmospheric Aerosols Sampled During Asian Dust Storm Periods in Taiwan

旨在针对2002年3￣4月亚洲沙尘影响台湾期间,探讨位于台湾海峡中间澎湖群岛之大气悬浮微粒物化特征变化情形。本研究在澎湖群岛的小门村设置悬浮微粒采样站,借以采集近海面之大气悬浮微粒。由悬浮微粒浓度变化情情得知,2002年3￣4月共有3次亚洲沙尘暴抵达澎湖群岛,其粒径分布很明显地由双峰分布(bi-modaldistribution)转变为以粗微粒(coarseparticle)为主之单峰分布(singlemodaldistribution)。此外,悬浮微粒中水溶性离子成分之粒径分布亦随亚洲沙尘之抵达而呈明显变化,其中Cl-和Na+之变化趋势具有一致性,显示海盐之影响颇为重要;NH4+、Ca2+和SO42-均由细微粒(fineparticle)转变为粗微粒,显示(NH4)2SO4或CaSO4应为亚洲沙尘之特征指纹;NO3-主要来自当地污染(localemission),故其分布并无明显变化;Mg2+虽维持以粗微粒为主之单峰分布,但其浓度却增加约2倍左右。上述研究结果显示,当亚洲沙尘抵达台湾地区,不仅悬浮微粒之粒径大小改变,就连化学组成亦出现明显变化。

This study investigated the size distribution and chemical composition of sea-level atmospheric aerosols at the Pescadores Islands during the Asian dust storm periods in the year of 2002. An Asian dust sampling station was originally established at Xiaumen of the Pescadores Islands that is located at the centre of Taiwan Strait. Monitoring data showed that there were three Asian dusts invaded the Pescadores Islands on March and April of 2002. The size distribution of atmospheric aerosols switched from single mode to bi-mode as Asian dusts arrived. Moreover, the chemical composition also varied during the Asian dust invasion periods. The variation of SO42-, NH4+, and Ca2+ size distributions at fine and coarse particle modes was quite consistent. An increase in SO42-, NH4+, and Ca2+ on coarse particle mode during Asian dust invasion periods suggested that they could accompany with the Asian dusts on the transportation route to the Pescadores Islands in the forms of (NH4)2SO4 and/or CaSO4. NO3- was abundant on coarse particle mode and no significant variation of NO3- distribution was observed between Asian and non-Asian dust invasion periods. This probably due to the fact that NO3- forming from nitrogen oxides was mainly emitted from local sources. Although Mg2+ stayed single particle mode, the concentration of Mg2+ increased approximately twice times as Asian dusts arrived. Furthermore, a backward trajectory plot of Asian dust storm episode arrived at the Pescadores Islands on March 8, 2002 was originally blown from Mongolia Area.