| 摘要: | 中文摘要 許多探討大氣輻射作用（Curry et al., 1995; Hegg et al., 1996）、酸性沈降機制（Zhuang et al., 1999a; Zhuang et al., 1999b）、雲霧形成機制（Tabazadeh et al., 1997; Hu and Abbatt, 1997）、區域能見度（Hanel, 1976; Tang, 1980）、氣膠化學組成與人體健康風險評估（Li et al., 1992; Li and Hopke, 1994）與許多熱力學模式及氣候變遷模式等，皆與大氣氣膠含水量有重大關係(Boucher and Anderson, 1995)。 本研究藉由建立GC/MS分析技術，瞭解大氣中常見的吸濕性有機氣膠二元酸與左旋葡萄醣的成分與含量，另外以GC-TCD氣膠含水量分析儀（Chang and Lee, 2002）量測有機氣膠與有機/無機混合氣膠的含水特性，探討大氣常見有機氣膠對典型無機鹽類的吸濕特性影響。 郊區大氣氣膠中總二元酸平均濃度為364±208 ngm-3，濃度範圍為13~906 ngm-3，總二元酸約佔PM2.5的1.8±1.2%、總碳成分的7.7±4.2%、有機碳的9.7 ±5.1%；從物種分布可知oxalic acid 最多，約佔總有機二元酸的76±12％，其次分別為succinic acid (C4)、malonic acid (C3)、glutaric acid (C5)與adipic acid (C6)。都會區大氣氣膠中總二元酸平均濃度486±217 ngm-3，濃度範圍為184~1049 ngm-3，總二元酸約佔PM2.5的1.2±0.5%、總碳成分的2.7±1.2%、有機碳的3.2±1.4% ；從物種分布可知也是oxalic acid 最多，約佔總有機二元酸的81±5％，其次分別為succinic acid (C4)、malonic acid (C3)、glutaric acid (C5)與adipic acid (C6)。在另外的醣類物種分析中，都會區大氣中左旋葡萄醣可作為燃燒氣膠的指標，且與碳成分有相同的趨勢。 在氣膠含水量研究方面，氣膠粒徑會影響glutaric acid有機氣膠的潮解點相對濕度（DRH），對於再結晶相對濕度（CRH）則較無影響。在有機/無機不同混合比例研究中(以oxalic acid與硫酸銨混合)，當oxalic acid有機含量愈高會使硫酸銨的DRH與CRH提早發生，混合氣膠含水量隨著有機氣膠的比例增加而下降。 在有機/無機相同混合比例研究中(以oxalic acid、malonic acid、succinic acid、glutaric acid和硫酸銨與氯化鈉進行混合)，oxalic acid不影響氯化鈉氣膠DRH，但會使硫酸銨的DRH提早，且均使兩種無機氣膠的CRH提早發生；malonic acid則使無機氣膠DRH提早，並延後其CRH；succinic acid不影響無機氣膠DRH，但使其CRH提早發生；glutaric acid不影響氯化鈉氣膠DRH，稍微提早硫酸銨的DRH，且均使CRH稍微提早。在含水量方面，只有glutaric acid會加強氣膠亞穩態水量，其他皆為抑制氯化鈉與硫酸銨的吸濕與亞穩態水量。整體而言，氯化鈉、硫酸銨受四種有機氣膠影響的含水量有不同的特性。 Abstract Hygroscopic aerosols are significant in aerosol radiative forcing, acid deposition, formation of clouds and fogs, regional visibility, climate change, and human health assessment (Curry et al., 1995 ; Hegg et al., 1996；Zhuang et al., 1999a ; Zhuang et al., 1999b；Tabazadeh et al., 1997; Hu and Abbatt, 1997；Li and Hopke, 1994). Recently, the effect of organic component of a mixed aerosol on its water content has drawn a great attention. The thermal-equilibrium model for inorganic-organic mixed aerosols apparently needs experimental data to validate. This study modified analytical methods for the determination of straight chain dicarboxylic acids (C2-C10) and levoglucosan in atmospheric aerosol using gas chromatography/mass spectrometry (GC/MS). In addition, a gas chromatography/thermal conductivity detector (GC/TCD, Chang and Lee, 2002) is applied for measuring water mass of pure dicarboxylic acids and internally mixed inorganic-organic aerosols. The objectives are investigating particle size on the humidogram of dicarboxylic acids and studying the effects of organic component to the aerosol water associated with inorganic aerosol typically found in the atmosphere. The average of total dicaroxylic acids (C2-C10) of rural aerosol at Shi-Men site was 364±208 ngm-3 and the percentages to PM2.5, total carbon, and organic carbon were 1.8±1.2%, 7.7±4.2%, and 9.7±5.1%, respectively. In contrast, the average of total dicaroxylic acids (C2-C10) of urban aerosol at Hsin-Chuang site was 486±217 ngm-3 and the percentages to PM2.5, total carbon, and organic carbon were 1.2±0.5%、2.7±1.2% and 3.2±1.4%, respectively. Oxalic acid (C2) was the most abundant dicarboxylic acid and was 81±5% and 76±12％ of total dicaroxylic acids at urban and rural site. For other important species, levoglusan is identified as a potential marker for biomass burning in atmospheric aerosol. In the study of aerosol hygroscopic properties, the results show bigger particle tends to retard water uptake of glutaric acid during deliquescence cycle but without a major influence on efflorescence cycle. Oxalic acid exerts its influence on reducing water uptake and lowering the DRH（Deliquescence Relative Humidity） and CRH（Crystallization Relative Humidity） of the inorangic component salt in a mixed aerosol. For inorganic aerosol (NaCl and (NH4)2SO4) mixed with organic aerosol (oxalic acid, succinic acid, malonic acid and glutaric acid) at the same mass ratio, the orangics show varied individual effects on the mixed inorganic aerosols. Oxalic acid exerts no influence on the DRH of NaCl but tends to lower the DRH of (NH4)2SO4. Malonic acid lowers the DRH of the associated inorganic salt and delays its CRH. Succinic acid has no effect on the DRH of the associated inorganic salt but makes its CRH occurring at higher RH. Glutaric acid shows no effect on the DRH of NaCl but slightly lower the DRH of (NH4)2SO4. Glutaric acid also pushes CRH of both inorganic salts to a slightly higher value. For the effect of organic component to the aerosol water of a mixed salt, glutaric acid is the only one which enhances metastable water content. In summary, the water content of NaCl and (NH4)2SO4 is influenced individually by the incorporated four organic components. |
