| 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，但是在實場進行現地AWC的直接量測非常少。本文發展出一套序列式氣膠含水量量測系統（Sequential Aerosol Water Measurement System, SAWMS），可以進行氣膠序列採樣，並經由量測三種常見的無機鹽類（NaCl、NH4NO3和 (NH4)2SO4）增溼與降溼過程中的AWC，比較熱力學模式模擬的AWC而得到驗證。本文進一步比較量測的AWC和氣膠學界常使用的H-TDMA（High Tandem Differential Mobility Analyzer）量測的氣膠體積變化，以推導出的氣膠質量變化（Aerosol Mass Change, AMC）、吸濕係數、成長因子關係式，發現量測的AWC與H-TDMA量測結果有可比較性。為了瞭解環境實場AWC變化，本文佈設SAWMS系統進行現地採樣與分析，於2019年在環境保護署的小港空氣品質監測站進行AWC量測，採樣期間SAWMS的AWC量測相對濕度設定在90%，PM2.5的平均AWC為39.0 ± 14.3 μg m-3比PM2.5監測平均值高出140%。濾紙分析完AWC後進一步解析水溶性無機離子（Water-soluble inorganic ions, WSIIs）含量提供ISORROPIA II模擬AWC，量測與模擬的AWC有非常好的相關性（R2 = 0.85; n = 39, p < 0.05）說明WSIIs貢獻大部分的AWC。本文選取三樣本進行多個相對濕度的增降濕分析以觀察AWC的變化，發現增濕過程中量測與模擬的AWC在60 – 80%相對濕度有較顯著的差異，可能因為在環境中氣膠實際的結合型態與混合狀態與模擬的有所不同。採樣期間氮氧化比與AWC有不錯的相關性（R2 = 0.70; n = 35, p < 0.05），代表AWC與NO3-的生成有關聯。
總結來說，本文發展出SAWMS進行序列氣膠採樣，並使用熱力學模式進行AWC量測的驗證，為了展現SAWMS現地量測AWC效能，本文在一個都市站點（小港）量測大氣氣膠的吸濕特性，連結AWC、WSIIs、環境因子，對瞭解氣膠影響都市能見度有大的助益。
;Aerosol water content (AWC) plays a significant role in secondary aerosol formation, aerosol-cloud interaction, and atmospheric visibility degradation. In field applications, direct measurement of AWC is rare. This study developed a sequential aerosol-water measurement system (SAWMS) capable of continuous aerosol collection and verified the measured AWC by comparing humidographs, generated with the SAWMS method in the laboratory, of three common salts (NaCl, NH4NO3, and (NH4)2SO4) with thermodynamic equilibrium models (ISORROPIA II, and E-AIM). To compare the SAWMS-measured AWC with volume-based measurements obtained in previous studies using H-TDMAs (High Tandem Differential Mobility Analyzer), the relationships of the hygroscopicity parameter () with aerosol mass change (AMC) and the growth factor (GF) with AMC were first derived. The derived and GF by AMC were comparable to those measured by H-TDMA. This study also deployed the SAWMS for in-situ measurements of AWC at the Taiwan Environmental Protection Administration Xiaogang (XG) site in Kaohsiung city. During the sampling period, the RH for the SAWMS measured AWC was set at 90% and the average PM2.5 concentration was 39.0 ± 14.3 μg m-3, which was 140% higher than the monitoring PM2.5 concentration. The WSIIs of aerosols on the filters were analyzed after AWC measurement, then applied to the ISORROPIA II model. The modeled and measured AWC was well-correlated (R2 = 0.85; n = 39, p < 0.05), indicating that WSIIs contributed the most to AWC. Humidographs were constructed to analyze the AWC values under varying RH levels during the humidification and dehumidification processes for the three selected samples. The humidification results revealed a significant difference between the measured and modeled AWC within 60 – 80% RH. This might be due to deviations in aerosol combination types and the mixing state from atmospheric conditions. The nitrogen oxidation ratio and the AWC were well-correlated (R2 = 0.70; n = 35, p < 0.05) throughout the sampling period, implying that the measured AWC was related to NO3- formation in the urban area.
In summary, this study developed SAWMS to collect aerosols and measure AWC simultaneously, and then verify the measured AWC by thermodynamic equilibrium models. To demonstrate the ability of SAWMS in a field experiment, this study investigated the hygroscopic nature of urban aerosols collected from the urban site (Xiaogang). Connecting the AWC to WSII and meteorological factors provides key links to the impact of aerosols on urban visibility. |
