台灣地區受境外傳輸及本污染影響之雲凝結核特性分析;Characteristics of cloud condensation nuclei under long-range transport and local pollution in Taiwan

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Title:	台灣地區受境外傳輸及本污染影響之雲凝結核特性分析;Characteristics of cloud condensation nuclei under long-range transport and local pollution in Taiwan
Authors:	謝惟任;Hsieh, Wei-Jen
Contributors:	大氣科學學系
Keywords:	吸濕性;雲凝結核;柯勒理論
Date:	2018-10-05
Issue Date:	2019-04-02 14:08:12 (UTC+8)
Publisher:	國立中央大學
Abstract:	大氣氣膠除了散射和吸收太陽輻射，也會改變雲的形成間接影響氣候。雲凝結核的微物理和化學組成對雲的發展和降水過程都為氣候變遷不確定性的主因之一，對此，知曉不同空間、時間分布及環境條件下的雲凝結核特性將有助於提升對不確定性的了解。本研究分為兩個部分，第一部分為2014至2016年於富貴角地區進行三年的觀測實驗，主要觀測東北亞境外傳輸影響下微粒於春冬兩季的吸濕特性；第二部分則是從2017年至2018年於台中地區進行連續觀測，此部分則探討台灣本地污染微粒於秋冬兩季的物化及吸濕特性。本研究中，雲凝結核的特性以活化率(AR = CCN / CN)來量化分析，由實驗數據顯示，富貴角的風向主要為東北風向及西南風向，歸類東北風向微粒受境外傳輸及無境外污染影響，西南風向則為本地污染。春季東北風向且受境外傳輸時，雲凝結核活化率沒有明顯較無受境外傳輸時期高，與幾何平均粒徑相關性低，且黑碳佔比較低。無境外污染事件影響時，黑碳佔比(BC/PM2.5)數值較冬季集中，且活化率與幾何平均粒徑呈稍正相關；冬季東北風且境外傳輸明顯污染事件發生時，活化率會明顯高於未受境外傳輸時，平均黑碳佔比與粒徑大小負相關較春季明顯，幾何平均粒徑的機率分布變化較春季為寬，且易出現大微粒，可能暗指春季時污染來源可能較為單一但老化程度較弱，而冬季微粒的來源路徑複雜且老化程度較高。無境外污染事件時，黑碳佔比的數值較春季分散。無論有無受境外傳輸影響，活化率與幾何平均粒徑皆有正相關性。西南風向所傳輸的微粒在春冬兩季並無太大差異，推論應該大部分皆是源自於相似污染源，主要為附近漁港的船隻影響。台中地區實驗期間活化率平均值為0.13，秋季和冬季由十月抵達台灣第一道鋒面的時間來區分。實驗數據顯示秋季的活化率高於冬季。再者，分析兩季節的微粒吸濕特性與風向的關係顯示，活化率和粒徑大小皆南風時為最高，東北風時最低。但黑碳佔比於西北風向時為最高，推測主要受到交通排放影響。本研究亦結合活化率和微粒粒徑分布(PSD)測量結果，估算Petters and Kreidenweis (2007)於Kӧhler理論架構下所提出的吸濕參數(κ)。活化率、粒徑大小和κ的分析顯示台灣中部地區的雲凝結核具有兩組不同的特性。一組顯示粒徑和活化率之間呈高正相關，吸濕參數較高，另一組則呈現相對較弱的相關性，吸濕參數較低。秋季的高吸濕性微粒成分硫化物體積佔比較高，發生的原因推測與溫度或微粒酸鹼值有關；冬季的高吸性微粒則多含較低的黑碳佔比，與境外傳輸資料比較，發現成因可能受境外傳輸影響，其現象也與富貴角相符。 ;In addition to scattering and absorbing solar radiation, atmospheric aerosols change the formation of clouds and indirectly affect the climate. The microphysical and chemical composition of cloud condensation nuclei is one of the main reasons of climate change and precipitation. It is useful to know the characteristics of cloud condensation nuclei (CCN) under different spatial, temporal distributions and environmental conditions. The study is categorized into two parts. The first part is a three-year observation experiment in Fuguei Cape from 2014 to 2016. This measures hygroscopicity of the particles in the spring and winter seasons under the long-range transport (LRT) from Northeast Asia. The second part is conducted in Taichung from 2017 to 2018. This section explores the physicochemical and hygroscopic properties of local polluted particles in Taiwan during the fall and winter seasons. In this study, CCN activities are quantified by activation rate (AR = CCN / CN). The experimental data showed that the wind direction of Fuguei Cape is almost northeast wind and southwest wind. Northeast wind particles are composed by LRT and non-LRT. Southwest wind particles are local pollution from Fuguei Cape. In spring, AR of the northeast wind particles under LRT is not significantly higher than that of the non-LRT period. The correlation with the geometric mean diameter (GMD) and AR is low, and the black carbon ratio is relatively low. In non-LRT period, black carbon ratio (BC/PM2.5) is more concentrative than winter, and the AR is slightly positively correlated with the GMD. In winter, AR of northeast wind particles under LRT with obvious pollution event is higher than non-LRT event. And black carbon ratio is negatively correlated with the particle size. The GMD probability distribution is wider than that spring, and it is prone to appear large particles, which may imply the source of pollution in spring may be simple and weaker aging process, while the path in winter is more complex and a higher degree of aging. In non-LRT period, the value of black carbon ratio is more dispersed than spring and AR is positively correlated with the GMD regardless of LRT or non-LRT. On the other hand, the properties of particles in southwest wind are similar in spring and winter seasons. Pollution sources should be the same which mainly originate from the ship emissions in nearby harbor. The average AR in Taichung area was 0.13, and fall and winter seasons are divided by the time of first cold front arriving Taiwan in October. Experimental data shows that the AR in fall is higher than winter. Furthermore, the analysis of the two seasons and the wind direction shows that the AR and particle size are the highest in the southerly wind and the lowest in the northeast wind. However, black carbon ratio is highest in the northwest wind, and this is mainly affected by traffic emissions. The experimental hygroscopicity, κCCN, proposed by Petters and Kreidenweis (2007) under the scheme of Kӧhler theory was further derived using AR and collocated particle size distribution (PSD) measurements. Analyzing AR, particle size and κ showed that particles in central Taiwan have two different characteristics. One group showed a high positive correlation between GMD and AR, where the hygroscopic parameters are high. The other group showed a relatively weak correlation, where the hygroscopic parameters are low. In fall, higher hygroscopicity particles contain more volume fraction of sulfate, which is presumably related to temperature or PH value of particles; in the winter, higher hygroscopicity particles contain lower portion of black carbon, which is more likely to be affected by LRT. This phenomenon is also consistent with Fuguei Cape.
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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