| 其他摘要 | The molecular compositions, temporal and seasonal variations of marine aerosols collected in Chichi-Jima (142°13'E, 27°04'N) Island in the western North Pacific were studied using a gas chromatography/mass spectrometry (GC/MS) technique. About 300 total suspended particle (TSP) samples were collected during two long-term periods from 1990 to 1993 and from 2006 to 2009. Air mass back trajectory analysis, hierarchical clustering (HC) method, principal components analysis (PCA), and positive matrix factorization (PMF) analysis were performed to discuss the sources and source apportionments of marine aerosols in the western North Pacific. Ten classes of organic compounds in the marine aerosols were identified, including n-alkanes, fatty acids, n-alcohols, saccharides, phthalates, polyacids, lignin and resin products, β-sitosterol, aromatic acids and PAHs. During both 1990 to 1993 and 2006 to 2009 periods, the total concentrations of saccharides were the highest (mean 14.8 and 38.6 ng m-3), followed by phthalates (6.0 and 18.4 ng m-3) and fatty acids (5.8 and 9.6 ng m-3). Concentrations of lignin and resin products, β-sitosterol, aromatic acids and PAHs were found to be very low campared to those of lipid compounds and saccharides. From 1990-1993 to 2006-2009, concentrations of most organic compound classes increased at different levels. However, the levels of organic species in the marine aerosols were 1-2 orders of magnitude lower than urban aerosols. The seasonal patterns of the identified organic species, including anhydrosugars (galactosan, mannosan and levoglucosan), high molecular weight (HMW) lipids (C25-37 n-alkanes, C20-34 fatty acids, C20-35 n-alcohols), aromatic acids, polyacids and PAHs, were characterized by winter/spring maxima and summer/fall minima, but low molecular weight (LMW) lipids (C18-24 n-alkanes, C9-19 fatty acids, C14-19 n-alcohols), lignin and resin products and β-sitosterol showed a different seasonal pattern. However, phthalates, sugars and sugar alcohols were found to be higher in summer/fall and lower in winter/spring during both 1990-1993 and 2006-2009 periods, indicating enhanced plastic and biogenic emissions in warm seasons. Ten-day air mass backward trajectory analyses were calculated to understand the source regions. About 95% of the air masses came from the Asian continents in winter, while more than two thirds were from the center of the Pacific and about one fourth from Southeast and South Asia in summer. In spring, more than 63% and 25% of the air masses came from the Asian continents and the center of the Pacific, respectively. In fall, more than half and about one third of the air masses were from the center of the Pacific and the Asian continents, respectively. The Asian continents include Mainland China, Mongolia, Siberia, Korea and the Japan Islands. The air masses from the Asian continents were heavily polluted and were rich in terrestrial organic matter, while those from the Pacific Ocean were clean with the influence of marine emitted organics. Higher values of average chain length (ACL) of HMW lipids were observed in the marine aerosols that were strongly influenced by the air masses from Southeast and South Asia. In general, the ACL of lipid compounds in aerosols from tropical plant emission showed higher values than those from subtropical and temperate regions. |
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