| 英文摘要 |
To investigate the chemical characterizations and spatial distributions of the aeolian dust emitted from the four riverbeds, namely, Da An River, Da Jia River, Da Tu River and Jhuoshuei River, and asses their impact on the air quality in the surrounding areas, two intensive particulate matters (PM) measurenments were conducted in the vicinity of all aforementioned rivers during the spring (northeast monsoon, NE) and summer (non-northeast monsoon) seasons in 2015. The dust samples emitted from bare lands of riverbeds and paved roads were also synchronously collected. Metallic elements, water-soluble ions, carbons and polycyclic aromatic hydrocarbons in most of the samples were analyzed by using ICP-MS, IC, carbon analyzer and GC-MS.
The result shows that the abundances of crustal elements such as Al, Fe, K, Na, Mg and Ca in each dust sample were very comparable; the higher concentrations of traffic-derived elements, including Mo, Zn, Pb, Sb and Cd, were found in paved road dust, leaving the inter-elemental ratios of Mo/Al, Zn/Al, Pb/Al, Sb/Aland Cd/Al to be the useful fingerprinting ratios to differentiate river dust from paved road dust. Moreover, the ambient PM in the areas near the rivers revealed that secondary inorganic aerosol (SIA, ~59%) was the most predominant species in the springtime, followed by organic aerosol (OC, ~14%), crustal material (13%) and elemental carbon (EC, ~4%). However, the significant contribution (~ 25%) of aeolian dust on ambient PM was only observed for Jhuoshuei River in the monsoon season. During the summertime sampling period, OC turned into the most abundant species, which accounted for 37% in the PM2.5 mass, followed by SIA (33%), EC (14%) and crustal materials (4%). The abrupt increase of OC might be due to the enhancements of secondary organic carbon. Because of calm condition, the influence of aeolian dust from all rivers on the ambient PM levels was insignificant during the non-monsoon season.
For PAHs, higher concentrations in summer was due to the meteorological condition of high temperature and low wind speed which would enhance the PAH concentrations in vapor phase. By using PMF model, we found the sources of PAHs in spring were stationary sources (34%), vehicle emissions (24%), coal combustion (23%) and petrochemical fuel gas (19%), while in summer the emission sources were petrochemical fuel gas (34%), the natural environment of volatile organic compounds (29%), coal combustion (19%) and stationary sources (18%). Finally, model simulation by WRF/Chem indicated that, comparing to the other three rivers, Jhuoshuei River was the most important source to release aeolian dust into atmosphere. Aeolian dust would transport as far as Kaohsiung City during the strong NE period and contribute a lot of PM to the atmosphere; nevertheless, the dust concentrations in inland areas were, in general, much higher than that in coastal areas.
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