| 摘要: | 氣膠含水量(Aerosol Water Content, AWC)在二次氣膠生成、雲與氣膠交互作用和大氣能見度降低中扮演重要的角色，本研究 於 2024年春季 在臺 中市區 採集
PM2.5 (氣動直徑小於或等於 2.5 m懸浮微粒 )以連續式氣膠含水量量測系統
(Sequential Aerosol Water Measurement System, SAWMS)量測 AWC，並 結合 PM2.5水溶性無機離子 (Water-soluble Inorganic Ions, WSIIs)變化，驗證 ISORROPIA-II及
E-AIM模式 準確度，以及觀察實地氣膠吸濕與混合行為。
本研究
於實驗室進行硫酸銨、硝酸銨、氯化鈉單一無機鹽的吸濕與降濕實驗
確認 AWC量測與 模式 模擬的一致性 。 隨後 進行 硫酸銨與硝酸銨 以1:1方式混合的內混合與外混合配置比較，結果 發現內、外混合氣膠都具有較單鹽潮解點提早特性，90% RH的 氣膠質量變化 與模式值相同， 外混合氣膠有兩段潮解現象。 本研究以草酸與檸檬酸代表有機酸，結果顯示兩者在30% ~ 90% RH範圍都呈現連續吸水現象，但都沒有出現潮解點。當這些有機酸與無機鹽(硫酸銨、硝酸銨)以1:1方式混合時，無機鹽能主導無機與有機混合鹽的含水量變化，模式模擬在含水量RH歷程變化與量測值具有差異，但90% RH的含水量則相近。在實地觀測方面，在90% RH，大氣PM2.5含水量會達到標準方法PM2.5質量濃度的100%。以標準方
法秤重環境控制的 30% RH環境中，氣膠殘留水分約佔乾 PM2.5質量濃度的 2 6%範圍。 臺中市AWC與PM2.5硝酸銨濃度呈現正相關，顯示AWC提升有助於硝酸鹽的二次生成。本研究 以 SAWMS量測 氣膠 AWC，並探討氣膠實際吸濕行為，搭配
熱力學平衡 模式 模擬與化學成分分析瞭解都市氣膠行為與混合特性， 研究成果對
於大氣相對濕度和氣膠化學成分的影響氣膠含水量有更深入的瞭解 。;Aerosol Water Content (AWC) plays a crucial role in secondary aerosol formation, cloud-aerosol interactions, and the reduction of atmospheric visibility. In this study, PM2.5 (particulate matter with an aerodynamic diameter ≤2.5 μm) was collected in Taichung City during the spring of 2024. A Sequential Aerosol Water Measurement System (SAWMS) was used to measure AWC. The variations in water-soluble inorganic ions (WSIIs) were also analyzed to validate the accuracy of the ISORROPIA-II and E-AIM thermodynamic models and to investigate in-situ aerosol hygroscopicity and mixing behavior.
In the laboratory, deliquescence and efflorescence experiments were conducted using individual inorganic salts, including ammonium sulfate, ammonium nitrate, and sodium chloride, to confirm the consistency between AWC measurements and model simulations. Further experiments compared internal and external mixtures of ammonium sulfate and ammonium nitrate (mixed in a 1:1 ratio). Results showed that both mixing types exhibited earlier deliquescence than individual salts. At 90% relative humidity (RH), the aerosol mass changes matched model predictions, with external mixtures displaying a two-step deliquescence pattern. Oxalic acid and citric acid were used to represent organic acids. Both showed continuous water uptake in the RH range of 30% to 90%, without a distinct deliquescence point. When mixed in a 1:1 ratio with inorganic salts (ammonium sulfate or ammonium nitrate), the inorganic salts predominantly governed the water content of the mixed particles. While model simulations differed from measurements in RH-dependent water uptake behavior, the AWC at 90% RH was comparable. Field observations showed that at 90% RH, the atmospheric PM2.5 water content could reach 100% of the standard-method PM2.5 mass concentration. Under the 30% RH condition of the standard gravimetric method, residual aerosol water accounted for approximately 2–6% of the dry PM2.5 mass. In Taichung City, AWC was positively correlated with ammonium nitrate concentrations, indicating that increased AWC facilitates the secondary formation of nitrate. This study used SAWMS to measure aerosol AWC and explore actual hygroscopic behavior. Combined with thermodynamic equilibrium modeling and chemical composition analysis, it provides insights into the behavior and mixing characteristics of urban aerosols. The results contribute to a deeper understanding of how relative humidity and aerosol chemical composition influence AWC. |
