| Ocean occupying over 71% of the Earth’s area is an important site for global biogeochemical cycling of substances. Ocean is under a substantial impact of continental materials particularly the coastal area. Long-range transport of Asian dust (AD) can carry large quantities of trace elements to the marginal seas of North Pacific, and the deposition of soluble fractions of aerosol elements may have significant impact on the primary productivity and planktonic community structure in these regions. This study investigates the seasonal variation, size distribution, sources, solubilities and dry deposition fluxes of trace elements in aerosols over the East China Sea (ECS), and verifies the importance of AD to atmospheric input of trace elements over the ECS. The main conclusions are listed below:1. Total suspended particle (TSP) and size-segregated aerosol samples are collected synchronously at Huaniao Island of the East China Sea (ECS) between April 2010 and March 2011 and then analyzed for total and soluble fractions of 22 trace elements as well as major ions. This study conducts a comprehensive investigation on the concentrations, solubility, size distribution and potential sources of atmospheric trace elements and their seasonal variation at Huaniao Island. Comparing with previous study, we have found that the concentrations of pollutant elements at Huaniao are comparable to those measured in Beijing and Qingdao, indicating a distinct impact of continental material on aerosol elements over the ECS.2.13 AD events are identified in spring and autumn of the sampling year based on atmospheric Al concentration and Fe/Al mass ratio. Most aerosol elements show significantly higher levels during AD compared to ND period, demonstrating a strong coupling between elemental concentrations at Huaniao Island and long-range transport of AD out of inland China. Besides, the concentrations of crustal elements Al, Fe, P measured at Huaniao Island are found to be significantly correlated with those observed in Shanghai city during ND days, which indicates the importance of city dust (dust from construction and road surface) to the elemental concentrations over the coastal ECS. AD and regionally-derived dust together can explain about 38% of the total variance of aerosol elements indicating that soil dust could be the major source for trace elements over the ECS. About 39% of the variance is caused by anthropogenic sources including coal combustion, heavy oil combustion, industrial emissions and biomass burning.3. Water-soluble fractions of aerosol elements are measured during the four sampling periods at Huaniao Island. It is found that the soluble fraction of metals would be higher in air masses of anthropogenic and marine origins. Unlike atmospheric concentrations, the highest solubilities are observed in late autumn for many elements (As, Ca, Cd, Pb, Cu, Mn and Sr) associated with primarily northwesterly wind that takes mainly anthropogenic pollutants from continental China to the ECS particularly coal burning products with high solubility. The mean solubilities decrease by a factor of 1/3 for majority of aerosol elements during AD period such as Al, Fe, Ba, Cd, K, Mn, Ni, Pb and V, which may be due to the substantial increase of total aerosol mass as well as the lower solubilities of these elements in crust than in anthropogenic emissions.4. Our estimates of dry deposition fluxes of soluble Al, Fe and Cu (10.4,2.1 and 1.9 μg m-2 d-1) are over an order of magnitude lower than those reported in previous study, which is mainly due to the distinct size distributions between soluble and total fractions of aerosol elements and the size-segregated samples used here for flux estimation instead of applying conventional deposition velocities by the previous study. The dry deposition flux of soluble P at Huaniao, about 4.0±1.8 μg m-2 d-1, could support 164 μg C m-2 d-1 of the carbon production. And the atmospheric dissolved Fe can sustain 21 mg C m-2 d-1, which means it almost impossible for Fe to be a limiting factor for phytoplankton growth in the East China Sea.5. The dry fluxes of total trace elements show significant increase during AD compared to ND period particularly for crustal elements Al, Ba, Fe, Mn, P, Sc and Ti. However AD events may have different impact on the dry fluxes of soluble fractions of various elements since the concentrations and solubility of majority aerosol elements increas and decline respectively during AD period. Under the impact of AD event, the increase in dry fluxes of soluble Fe and P (nutrients) and decrease in soluble Cu flux (potentially toxic) may promote episodic phytoplankton growth and is a potential trigger for algal bloom in the ECS. |
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