| 摘要: | 本研究探討台南郊區2005年5月至2008年12月底止，包括梅雨季節、颱風降雨與颱風外圍環流、夏季、秋冬乾季降雨及春季降雨之濕沉降特性，主要探討降雨的酸鹼度、無機鹽類及低分子量之二元有機酸之當量濃度變化及其相關性。
在台南郊區不同季節降雨型態之平均降雨，酸強度由高至低依序為秋冬乾季、梅雨季節、颱風外圍環流雨水、夏季、颱風降雨及春季，其pH值分別為5.29、5.32、5.45、5.46、5.56及5.74，而降雨的pH是由酸性離子SO42-、NO3-、HCO3-及鹼性離子NH4+、Ca2+所共同決定。各季節降雨中物種組成成份，所佔百分比不同，其中在颱風濕沉降中Cl- (24.56±26.24%)、Na+ (28.08±22.72%)及Mg2+ (8.24±4.30%)佔降雨物種當量濃度比例最高，在夏季濕沉降中，Na+(18.21±29.48%)佔降雨物種當量濃度比例很高，而在春季濕沉降中，Ca2+(22.06±14.24%)佔降雨物種當量濃度比例最高。此外五種濕沉降型態中，平均而言，二元有機酸佔物種組成成份的(0.25－0.53%)，二元有機酸均以oxalic acid為主要物種。
三種二元有機酸在各降雨型態中，以春季濕沉降所佔已分析物種組成比例為最高，主要乃因春季時期長期沒有降雨，而在降雨時，降雨雨量少及降雨強度小，導致濕沉降中之三種二元有機酸當量濃度較其他降雨型態為高。比較不同季節型態之二元有機酸之malonic acid:succinic acid (M:S)比值，在梅雨季節、颱風降雨、夏季、秋冬乾季及春季降雨型態的M:S比值，分別為1.84、0.82、1.20、1.50及1.56，其值介於低比值(0.3－0.5)與高比值3之間，由梅雨季節、颱風降雨、夏季、秋冬乾季及春季降雨型態逆軌跡圖所示，顯示降雨物種經長程傳輸，從海上吹經高雄市區，降雨之部份來源為市區交通的污染排放和在海洋上產生的光化產物溶入降雨中，在颱風外圍環流型態的M:S比值為4.54，其M:S的比值高於3，由颱風外圍環流降雨型態逆軌跡圖顯示降雨中之物種來源主要為顯示降雨明顯溶入光化產物的貢獻。
In this study, characteristics of the wet precipitation of the Mei-yu rain, typhoon precipitation and typhoon peripheral circumfluence and winter and spring in suburban Tainan from May 2005 till December 2008 were investigated. The investigation covered the acidity, inorganic salts and low-molecular-weight dicarboxylic acids (low-Mw DCAs) to study their equivalent concentration variations and correlations.
For the various seasonal precipitation patterns in suburban Tainan, according to the acidity decreasing magnitudes, the rainwater pH values are 5.29 for winter precipitation 5.32 for the Mei-yu rainy season, 5.45 for typhoon peripheral circumfluence, 5.46 for summer shower, 5.56 for typhoon precipitation and 5.74 for spring precipitation. The pH is dependent on presence of anions, e.g. SO42-, NO3- and HCO3- as well as cations, e.g. NH4+ and Ca2+ in the rainwater.
Further, as the percentage compositions of all chemical species in the various precipitation patterns are concerned, the typhoon wet precipitation has the highest percentages of Cl- (24.56±26.24%), Na+ (28.08±22.72%) and Mg2+ (8.24±4.30%). In summer wet precipitation, Na+ has the highest equivalent concentration percentage of (18.21±29.48%) while in spring wet precipitation, Ca2+ has the highest equivalent concentration percentage of (22.06±14.24%).
Additionally, in all 5 types of wet precipitations, the average percentage of low-Mw DCAs constitutes (0.25±0.53%) of all chemical species. Oxalic acid is the major constituent among all low-Mw DCAs.
These three low-Mw DCAs have the highest percentages of all analyzed chemical species in spring wet precipitation. This is mainly because that there is little precipitation in winter and the occasional precipitations have small quantities and intensities thus leading to higher observed equivalent concentrations of low-Mw DCAs than observed for other patterns of precipitation. The ratios of malonic acid to succinic acid (M:S ratio) are 1.84 for the Mei-yu rainy season, 0.82 for typhoon precipitation ,1.20 for summer precipitation,1.50 for winter precipitation and 1.56 for spring precipitation. All these ratios are between the low ratio (0.3－0.5) and the high ratio (3) ranges. Based on the backward trajectories for these three precipitation patterns, the chemical species contained in the rainwater have been subject to long-range transportation to be blown from sea to Kaohsiung downtown. Some chemical species originated from local municipal traffic-related pollution react photo-chemically with the species from the ocean and the products are dissolved in the rainwater. typhoon peripheral circumfluence M:S ratios of 4.54, which is higher than 3. The backward trajectories for both precipitation patterns indicate that the main chemical species in the rainwater mainly come from the species from the ocean and the products are dissolved in the rainwater. |
