長程傳輸對台灣北端氣膠酸鹼度與污染物演化生成程序的影響

The influence of long-range transport on aerosol acidity and pollutant evolution at northern tip of Taiwan

方彥仁(Yan-Ren Fang)

指導教授 ： 李崇德

國立中央大學/工學院/環境工程研究所/碩士(2006年)

摘要

近年來大陸沿岸工業污染排放及沙塵的傳輸日漸受到重視，這些污染物會隨著大陸性冷高壓及盛行東北季風傳輸至台灣。本文在台灣最北端的台北縣石門鄉進行空氣污染物觀測，採樣時間為2005年6月~ 2006年4月。夏季石門地區污染物的濃度值較低，秋、冬、春三季則是受到大陸長程傳輸的影響污染物的濃度值較高。採樣地點二氧化硫(SO2(g))大多是來自台北盆地，雖然SO2(g)濃度在冷高壓和黃沙時期時明顯較高，但發生時間只佔採樣時間的5%，SO2(g)從台北盆地傳輸而來的時間則約佔整個採樣時間的70%左右。氨氣(NH3(g)) 也是以本地污染來源為主，但如果沙塵前緣氣團有通過大陸沿岸，則往往在沙塵前緣先帶來大量的NH3(g)。硝酸氣(HNO3(g))及亞硝酸氣(HNO2(g))在各種氣流傳輸類型下並無明顯變化。在氣膠及其前驅氣體濃度分布上，石門的氣膠濃度較前驅氣體濃度為高。
非受沙塵影響時，四種逆溯氣流軌跡類型以大陸沿岸傳輸所帶來的二次氣膠含量較高，本地污染來源、海洋傳輸和高壓迴流則以一次氣膠的含量較高。當受沙塵影響時nss-Ca2+和二次氣膠有很高的相關性。此外，受大陸沿岸傳輸影響時nss-SO42-和SO(2)有很高的相關性，且nss-SO42- / SO(2)的濃度比也較低。
氣膠碳成分在夏季濃度較高，受大陸性冷高壓及東北季風影響時，濃度卻有降低的情形，顯示石門氣膠碳成分濃度主要是來自於台灣本島。從估算的石門二次有機碳濃度變化與低溫揮發的碳成分(OC2)有一致的變化，顯示OC2的來源可能與二次有機碳有關。
由氣膠酸鹼度(pH)可發現，石門氣膠多呈現酸性，主要是受到非海鹽硫酸鹽(nss-SO42- )的影響。比較不同氣團軌跡來源，由海洋傳輸而來的氣膠酸度較小；由大陸傳輸而來的氣膠，微粒酸度較高。由NH4+ / nss-SO42- 莫耳比的計算顯示，本地污染來源、海洋傳輸、高壓迴流及受沙塵影響期間，大氣環境多屬於ammonium-rich 的狀態。相對地，大陸沿岸傳輸則為ammonium –poor 的狀態。
在非黃沙時期及受黃沙影響時，succinic acid的含量明顯較低，且C3/C4的比多在1以上，此時二元有機酸以二次轉化形成為主。當受黃沙後高壓迴流影響時，氣流帶來較多的succinic acid，且C3/C4的比多介於0.4 ~ 0.6之間，顯示二元有機酸的形成也轉為以一次排放為主。

關鍵字

亞洲沙塵 ； 氣膠化學成分 ； 氣團軌跡來源 ； 氣膠前驅氣體

並列摘要

Recently, the industrial outflow and yellow-dust transported from China gained a lot of attentions. These pollutions may be transported to Taiwan by cold continental high-pressure system and northeast monsoon. In this study, filter-based aerosol was collected at Shi-Men site, the northern tip of Taiwan, from June 2005 to April 2006. The concentrations of air pollutants are lower in summer, while that in the other three seasons are higher.
The SO2 at Shi-Men site is found transported mostly from Taipei Basin. Although the concentration of SO2 tends to increase during yellow-dust and cold high-pressure affecting periods, the occurrence time shares only 5% of the sampling time. In contrast, the time when SO2 transported from Taipei Basin is around 70% of the aerosol observation time in this study. Similarly, NH3 is also produced locally most of the time, however, a great amount of NH3 is observed if the front of dust flow passes through the industrialized China’s coastline. Meanwhile, the distributions of HNO3 and HNO2 make no difference among different air masses. For the abundance compared between aerosol and precursor gases, aerosol concentration is found higher than its precursor gases.
The secondary aerosol is higher for China’s coastline transport, while primary aerosol is more contributed from local sources, oceanic transport, and anticyclonic outflow for the four types of back trajectory during non-dust period. A high correlation is found between nss-Ca2+ and secondary aerosol when under the influence of yellow-dust. Moreover, a consistent relationship is observed between nss-SO42- and SO2 for air masses transported from China’s coastline.
Aerosol carbon is mainly contributed from Taiwan as it shows high concentration in summer and low value in winter when under the influence of continental cold high and northeast monsoon. The variations of estimated secondary organic carbon are consistent with low-temperature volatilized carbon fraction OC2, it suggests that the sources of OC2 are related to secondary organic carbon.
The measured aerosol pH values are acidic which might be affected by the abundance of nss-SO42-. The lowest aerosol acidity is observed when the air masses are transported from the ocean, while aerosol acidity is the highest for China’s coastline transport among the four back trajectory types. The calculation of NH4+ / nss-SO42- molar ratios shows that the atmosphere is in the state of ammonium-rich when the air masses are from local area, the ocean, anticyclonic outflow, and yellow-dust transport. In contrast, the state of ammonium poor is found when the air masses pass through China’s coastline.
For most of the time, the amount of succinic acid is obvious the lowest among the analyzed dicarboxylic acids. It indicates that dicarboxylic acids are converted from secondary photochemical reactions as C3/C4 ratios are mostly above 1. However, the C3/C4 ratios are turned to vary from 0.4 to 0.6 when under the influence of anticyclonic outflow after the passage of yellow-dust. This then suggests that the formation of dicarboxylic acids is shifted to originate from primary emissions.

並列關鍵字

Asian dust ； Aerosol chemical properties ； Air trajectory ； Aerosol precursor gases

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