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Seasonal distributions of low molecular weight dicarboxylic acids, ketoacids and α-dicarbonyls in ambient aerosols collected at Cape Hedo, Okinawa, an outflow region of Asian dusts

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Title: Seasonal distributions of low molecular weight dicarboxylic acids, ketoacids and α-dicarbonyls in ambient aerosols collected at Cape Hedo, Okinawa, an outflow region of Asian dusts
Other Titles: 沖縄辺戸岬で採取したエアロゾル中の低分子ジカルボン酸と関連有機化合物の組成分布の季節変化
Authors: Kunwar, Bhagawati Browse this author
Issue Date: 25-Mar-2014
Publisher: Hokkaido University
Abstract: Ambient aerosol samples were collected for one year in Cape Hedo, Okinawa, the southernmost main island of Japan and studied for water-soluble dicarboxylic acids, ketoacids, and α-dicarbonyls to better understand the formation/transformation pathways of organic aerosols during long-range atmospheric transport. Here, we report the seasonal variations of diacids and related compounds in Okinawa, the outflow region of Asian dusts in the western North Pacific. We found that oxalic acid is the most abundant diacid species followed by malonic (C3) and succinic (C4) acids whereas glyoxylic acid is a dominant ketoacid. Total diacids and ketoacids maximized in spring when air masses originated from the Asian Continent under westerly winds. In contrast, α-dicarbonyls showed maximum concentrations in winter. The C3/C4 ratios were found to increase in summer, suggesting an enhanced photochemical aging of organic aerosols. Both phthalic acid (Ph)/C9 and C6/C9 ratios peaked in winter, suggesting an enhanced transport of organic pollutants from East Asia. The average total diacid-C/total carbon ratio (5.4%) is higher than that (3.1%) from the East China Sea but lower than from the remote Pacific including tropics (8.8%), suggesting that Okinawa aerosols are more aged than East Asian aerosols. This study demonstrates that the ambient aerosols from Cape Hedo are strongly influenced by the outflow of Asian pollutants in winter/spring and by photochemical processes of marine-derived organic matter in summer. In addition, we analysed organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), total nitrogen (WSTN) and organic nitrogen (WSON), and major inorganic ions. The average concentration of OC is higher in growing seasons; spring(2.36 µgm-3) and summer (1.79 µgm-3). Similarly, the highest concentrations of EC and WSOC were found in spring (av. 0.41 µgm-3 and 0.95 µgm-3, respectively) followed by winter (0.37 and 0.90 µgm-3) whereas the lowest concentrations were found in summer (0.19 and 0.52 µgm-3, respectively). Higher concentration of WSON were observed in early summer (av. 0.26 µgm-3) probably due to the emission from marine biota. The relatively high OC/EC (av. 7.6) and WSOC/OC (44%) ratios suggest the secondary formation of organic aerosols. A strong positive correlation between Ca2+ and TSP in spring suggests a significant contribution of Asian dusts whereas the higher concentrations of NO3- and nss-SO4 2- in winter suggest an important influence from anthropogenic sources including biomass burning, vehicular emission and coal combustion. Moreover, stable carbon (δ13C) and nitrogen isotope ratios (δ15N) were determined for total carbon (TC) and nitrogen (TN). The annually averaged δ13C and d15N ratios are - 22.1‰ and +12.2‰, respectively. The seasonally averaged δ13C and d15N ratios are higher in spring (-22.5‰ and +14‰, respectively) whereas these ratios are lower in summer (-22.9‰, +11.1‰). However, no correlation was obtained between nss-Ca/TSP and δ13C, suggesting that during long-range atmospheric transport organic aerosols are intermixed with various sources. A strong correlation between TC and TN in spring (r2=0.78) and winter (0.70) suggests that TC and TN have similar sources. Contributions of NO3- to TN are higher (45%) than those(18%) of NH4+, suggesting that vehicular exhaust and biomass burning emissions are more important nitrogen sources than the emissions from agricultural wastes and animal excreta.
Conffering University: 北海道大学
Degree Report Number: 甲第11342号
Degree Level: 博士
Degree Discipline: 環境科学
Examination Committee Members: (主査) 教授 河村 公隆, 教授 吉川 久幸, 准教授 関 宰, 助教 宮崎 雄三, 准教授 村尾 直人 (大学院工学研究院)
Degree Affiliation: 環境科学院(地球圏科学専攻)
Type: theses (doctoral)
Appears in Collections:学位論文 (Theses) > 博士 (環境科学)
課程博士 (Doctorate by way of Advanced Course) > 環境科学院(Graduate School of Environmental Science)

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