Atmospheric Deposition Of Nitrogen Species Over The China Sea And Its Impact On A Spring Bloom

Atmospheric nitrogen deposition provides an important supply of nutrients to the oceans and exerts a large influence on marine ecosystem. Beside bioavailability inorganic nitrogen, water soluble organic nitrogen is an important component in atmospheric nitrogen deposition. The bioavailability of water soluble organic nitrogen varied a lot in different components and it is also associated with their origins. To evaluate the effect of atmospheric nitrogen deposition to the marine ecosystem, the composition, sources and abundance of organic nitrogen should be determined. It was reported that a high value occurred in the China Sea has on the global map of atmospheric nitrogen deposition. However, these estimates only reflect contribution from inorganic nitrogen. In China, however, there are strong emission sources of organic nitrogen on fossil fuels, fertilizer production and application and aeolian dust. The current estimates of atmospheric nitrogen input to the China Sea should be significantly underestimated. Determination of organic nitrogen in the atmospheric aerosols over the China Sea would fill up knowledge gap on organic nitrogen and improve accuracy of atmospheric nitrogen input to the China sea. This thesis aims to characterize nitrogen species in aerosols over Qingdao, Qianliyan Island and Yellow Sea. The sources, compositions, distributions and abundance of water soluble organic nitrogen (ON) in aerosols, and the atmospheric nutrients input to the Yellow Sea and associated with the bloom biota responses are investigated. The main results are listed as below.In Qingdao, the contribution of particulate ON to total nitrogen (TN) is 23.7±16.5%. The mean concentration of ON is 256±303 nmol·m^-3 and much higher than those reported world widely, which was attributed to strong emissions of ON precursors such as NOx, NH3, soot and VOC in China. The ON concentration shows the high values occur in winter and spring, and the low values occur in autumn and summer. The concentration of ON in aerosols was found to be associated with the weather conditions. During haze and fog episodes, the concentrations of particulate ON are 2³ times higher than those during clear weather conditions, indicating a significant contribution of ON from secondary atmospheric reactions. ON shows strong correlation to NO₃^- and NH₄⁺ that further support this point. During the winter heating period, the ON concentration in aerosols shows statistically significant enhancement, suggesting a primary emission of ON from fossil fuels combustion. Water soluble total amino compounds contributes 7.5±5.0% to total organic nitrogen in aerosols. Combined amino compounds (CAC) accounts for the major portion of the amino compounds and its concentration is about 3 times greater than that of free amino compounds (FAC). Arginine (Arg.), methylamine (MA) and alanine (Ala) typically are the most abundant amino compounds in Qingdao. The transport path and the origin of air mass and weather conditions during the collection of aerosols appears to influence the concentrations and compositions of FAC and CAC. Urea contributes 7.5±5.0% to total organic nitrogen. The urea concentrations in Qingdao are higher than those reported for the other regions in the world, probably due to strong emissions derived the high usage of urea as a fertilizer in China.In Qianliyan, the ON contribution to TN is 22.8±12.9%, agreeing with those averaged values observed in Qingdao and the other regions in the world. The ON mean concentration is 111±81 nmol·m-3, much higher than that of the other regions in the world, but lower than that of Qingdao. This result may be due to the long-range transport of high levels of anthropogenic components from the big cities such as Beijing and Tianjing upwind of Qianliyan. The seasonal trend of ON concentration is consistent with that of Qingdao. The concentration of ON in aerosols, like Qingdao, is also significantly affected by the weather conditions. ON shows significant correlation to NO₃^-, NH₄⁺, K⁺, Cl- and Ca²⁺, indicating that the anthropogenic input and continental-derived dust are the major sources of ON in Qianliyan. Water soluble total amino compounds contributes 12.4±12.6% to total organic nitrogen. Arg. and MA typically are the most abundant amino compounds. MA shows significant correlation to NH₄⁺, NO₃^- and SO42-, suggesting that anthropogenic source is the major provider of MA. The urea concentrations in Qianliyan are lower than those of Qingdao, but higher than those reported for the other regions in the world where are not influenced by the polluted air mass. The urea concentration shows the high values occur in winter and spring, and the low values occur in autumn and summer, agrees with that of Qingdao. Urea contributes 5.3±3.8% to total organic nitrogen, therefore, about 80% of ON in Qianliyan aerosols are unidentified in this study. ON contribute ³0% of the total water-soluble particulate nitrogen over the South China Sea and ²0% over the Yellow Sea and in Qingdao. On average, the ON concentration over the Yellow Sea is higher than that of over the South China Sea, but lower than that of Qingdao. Over the marginal sea of China, more than 70% of the ON exist in the fine mode particles (<2.1μm). About 10% of the ON exists in the 7.0-11.0μm large particles and the part of the ON might be entrained sea-salt particles. During the dust storm periods, the concentrations of ON in the dust aerosols significantly increase but the contribution of ON to the total nitrogen decrease. In the dust aerosols, the contribution of ON increase by 20% in the coarse mode (>2.1μm), indicating the entrainment of large soil particles or dust material and/or the adsorption of coarse minerals on the aerosols. Factor analysis indicates that ON mainly originate from anthropogenic sources while a relatively small amount is from marine and crustal sources. Urea, on the average, represents ⁸% of the total ON over the marginal sea of China. In the non-dust aerosols, ⁵0% of urea exists in the fine mode over the Yellow Sea and Qingdao, but the percentage decrease to ³0% in the dust aerosols. Free amino acids is generally a minor component of the ON, only accounting for～1% of the total ON. Positive matrix factorization analysis indicates that ON mainly originate from four sources; they are marine, crustal, anthropogenic, and vehicles exhaust sources, respectively. Marine sources contribute 18.0%, crustal sources 25.3%, anthropogenic sources 41.7% and mobile emission sources 15.0% of total ON variance in the aerosol samples over the Yellow Sea. The deposition fluxes of total nitrogen in the Yellow Sea from February to April 2006 are estimated. The contribution of anthropogenic sources to the TN deposition is predominant among these four sources with the value of 66%. The other sources contributions are 9.8% of marine sources, 9.2% of crustal sources and 15% of vehicles exhaust sources, respectively.A cruise campaign in spring 2007 over the Yellow Sea ran into a couple of Asian dust episodes which were followed by blooms. The particle nutrients and iron concentrations, their solubility, size distributions and deposition fluxes during the dust and normal days were investigated. The concentrations of total P, total Fe and TIN (NH₄⁺, NO2- and NO₃^-) in TSP vary from 0.01 to 1.05μg·m^-3, 1.0 to 121.8μg·m^-3 and 1.21 to 22.28μg·m^-3 with the maximum concurrently with the dust storm events. On average, the solubility of Fe is 1.65 % in the dust aerosols and 8.46 % in the non-dust aerosols, respectively. The size distributions of particle mass, NO^3- and NH₄⁺ exhibit that their contributions increase by about 50%, 20% and 20% in the coarse mode, respectively, during the dust storm relatives to the normal days. During this dust event (31 March to 1 April, 2007), the dry deposition fluxes of soluble iron, soluble phosphorus and total inorganic nitrogen increase by a factor of ¹5, ¹3 and 5 relative to the non-dust level, respectively. The dust deposition scavenged by the precipitation accompanied with dust is extrapolated using the dissolved Al increment in the surface ocean. The result shows that the total atmospheric deposition for soluble Fe, soluble P and inorganic nitrogen over the Yellow Sea during the dust episodes are 42.5±10.9 mg·m-2, 10.3±2.6 mg·m-2 and 77.2±19.8 g·m-2, respectively, of which the wet depositions of nutrients is absolutely governed in the total depositions. During the dust event, the atmospheric input instead of the oceanic input from bottom dominates the supplies of nutrients in the surface water in the central Yellow Sea. When comparing estimations of the dust-derived nutrient supplies with plankton community needs, we found that the dust-derived N supply nearly satisfied the bloom phytoplankton need in the initiation of bloom; while, the dust-derived Fe supply far exceeded the total need of bloom biota. Granger causality test result shows that the dust-derived N, P and Fe depositions are the Granger causes of the subsequent biological response with 3-5 days extra lags, suggesting that the dust deposition has causality with the initiation of spring bloom in this case and the fertilization effect of dust-derived nutrients is the key factor in causing this spring bloom.