中国东海近海大气气溶胶的陆源特征、污染混合机理及干沉降量的估算

【作者】 吴天；

【导师】 郑志坚；

【作者基本信息】 复旦大学 ， 环境科学， 2010， 硕士

【摘要】 地球70%以上面积被海洋覆盖,海洋气溶胶是大气气溶胶的重要组成部分。海洋气溶胶是云的重要凝结核,对云雨形成有着重要作用。海洋是开放的系统,特别是近海,受陆地影响很大。每年十月至次年四月,亚洲沙尘会随气团运动朝太平洋输送,为海洋生物带来丰富的N、P、Fe等营养物质。同时,沙尘传输也会将沿途的污染物输送到下风向区域。矿物气溶胶和其携带的污染物在传输途中会混合转化,它们到达近海后,还会进一步和海盐粒子发生混合作用,改变近海大气的理化特征。另外,气溶胶会通过干、湿沉降作用进入海洋,影响海洋初级生产力。随着人们对赤潮、酸雨及全球变暖等问题的重视提高,近海大气气溶胶的研究已成为国内外研究关注的焦点之一。本论文通过气溶胶地面采样站点于2008年3月20日至2009年2月18日在东海小洋山岛采集了共计210个样品,分析了气溶胶质量及其重要组分的浓度、可溶性离子和元素。同时,在临近的大城市—上海,也进行了同步采样,分析了其中的黑碳。本文得到了东海近海,以小洋山岛为代表的大气气溶胶的季节分布和理化特征,估算了矿物气溶胶的贡献量和主要来源地；分析了硫酸盐、硝酸盐和黑碳的来源,以及元素污染水平；讨论了在陆源输送影响下,海陆气溶胶的混合特征及近海气溶胶理化特征的变化,并粗略计算了气溶胶中可能对海洋初级生产力有影响的离子／元素的干沉降量。研究结果对区域环境质量的改善和应对赤潮、酸雨和全球变暖等问题有重要启示。具体研究结果如下：东海近海大气气溶胶的浓度在世界范围内处于较高水平。PM2.5和TSP的年平均浓度分别为72.5和119.2μgm-3。PM2.5几乎为世界卫生组织规定的年平均浓度25μg m-3的三倍,且在90%的采样天数里,PM25的值都超过了WHO的日均浓度标准-35μgm-3。气溶胶及其组分的质量浓度及粒径分布具有显著的季节差异。在PM2.5中,TWSI、BC、SO42-、NO3-、NH4+和元素Al,K,Mn,Sr, Ti,P,Co,Ni,V,Cr,Cu,Pb,S的季平均最大值出现在冬季,而在TSP中,TWSI、SO42-、NO3-和元素Al,Fe,Mg,Na,V,As, S,Zn的季平均最大浓度出现在春季。冬季,TSP中约76%的气溶胶是细颗粒物；而春季,TSP中50%以上的的气溶胶分布在粗颗粒物中。PM25和TSP中总水溶性离子(TWSI)的年平均值分别为17.1μgm-3和33.3μgm-3占质量浓度的25%和29%。主要离子是：SO42-、NH4+、NO3-、Cl-、Na+和Ca2+,这六种离子之和占PM2.5和TSP中TWSI的79%和80%。这些离子可能的存在形式是：NH4HSO4和(NH4)2SO4，NH4NO3,CaSO4, Ca(NO3)2, CaCl2, MgCl2, NaCl,KNO3和K2SO4,春季还可能存在NaNO3。气溶胶样品浸提液的pH值和C/A的数值分析显示,东海小洋山岛的大气环境全年总体呈现酸性。这可能是由于污染气体SO2和NOx等在矿物气溶胶CaCO3表面发生了非均相反应生成了SO42-和NO3-的结果,它们与海盐离子NaCl甚至会发生置换反应,造成了氯缺失现象,使近海大气环境进一步恶化。除夏季数据以外,nss-SO42-和BC在其他季节的相关系数都在0.55以上,且斜率值比较接近0.07,这反应了东海近海域可能受到长三角化石燃料燃烧排放的影响。excessK/BC的分析表明,在PM25中,生物质燃烧对K和BC的贡献要大于化石燃料燃烧的贡献。上海和小洋山岛的BC数据在春季和冬季的相关性系数分别为0.66和0.83,这说明在气团运动影响下,上海对东海小洋山岛大气气溶胶中BC的影响显著。以元素Al为参比的富集系数(EF)分析表明,东海小洋山岛元素污染特征与城市的类似,这进一步反应了东海近海大气的陆源性。海陆源分析得知,海洋气溶胶和矿物气溶胶对PM25和TSP的贡献之和,平均仅为9%和19.4%,且气溶胶的质量浓度、主要离子和元素在WNW或NW的风向条件下,平均值最大。这说明陆地和人为活动可能是这一海域气溶胶更为重要的来源。采样期间,东海小洋山岛74%的采样天数受到了陆风的影响,且各季节气溶胶浓度最高值出现的采样日都显著受到了陆地气团的影响。气溶胶通过干沉降作用,可能对近海生态系统和区域气候环境产生影响。更多还原

【Abstract】 More than 70% area of Earth covered by oceans, marine aerosol is an important type of atmospheric aerosols. Also marine aerosol is critical cloud condensation nucleus, playing an important role on the formation of clouds and rain. Ocean is an open system, especially adjent sea, greatly affected by continent. During every period from October to next April, Asian dust with the air mass movement toward the Pacific Ocean will be transported to rich marine life of N, P, Fe and other nutrients. Meanwhile, the pollutants along the way will be transported to the downwind area. Mineral aerosols and its carrying pollutants will be mixed on the way and transformed. After they reached coastal region, they may further mix with sea salt, so the atmosphere of physical and chemical characteristics will change. In addition, the aerosol would affect the marine primary productivity through wet and dry deposition. As people have been paying more attentation on the environmental problems of Red Tide, acid rain and global warming, atmospheric aerosols of adjent sea has become one focus of domestic and foreign research.A total of 210 samples were sampled from Mar.20,2008 to Feb.18,2009 on the surface land of Xiaoyangshan Island on East China Sea, analyzing their mass concentration, water soluble ions and elements. Meanwhile, it was simultaneously sampled in neighboring city—Shanghai and analyzed black carbon. The main contents of this research were:the seasonal distribution of atmospheric aerosol of adjent sea and its physical and chemical characteristics represented by Xiaoyangshan Isle; estimating the contributions of mineral aerosols and its main continental source; analyzing the sources of sulfate, nitrate, black carbon and the level of elemental pollution; discussing the mixing mechanism of continental aerosol with sea salt and the change of physical and chemical characteristics under the influence of terrene;and calculating the dry deposition flux of main compounds in aerosols. The research will help control regional environmental quality and resvole the problems of acid rain and global warming. The results were as follows:The aerosol concentration of Xiaoyangshan Isle on East China Sea is in a high level over the world. The annual average concentrations of PM2.5 and TSP were 72.5μg m-3 and 119.2μg m-3 respectively. The value of PM2.s was about as three times as the annual standard of World Health Organization--25μg m-3.Also more than 90% of sampling days, the mass concentration of PM2.5 were more than the daily standard of WHO--35μg m-3.It showed a significant seasonal variation of aerosol and its composition and size distribution.In PM2.5, the seasonal average concentration of TWSI,BC, SO42-, NO3-, NH4+ and elements Al,K, Mn, Sr, Ti, P, Co, Ni, V, Cr, Cu, Pb, S was highest in winter; in TSP, that value of TWSI, SO42-, NO3- and element Al, Fe, Mg, Na, V, As, S, Zn was maximum in spring. In winter, about 76% of the aerosol in TSP were fine particules; while more than 50% of aerosol in TSP was coarse mode in spring. The annual average concentration of total water-soluble ions (TWSI) in PM25 and TSP was 17.1μg m-3 and 33.3μg m-3, which contributed about 25% and 29% to mass concentration. Major ions were:SO42-, NH4+, NO3-, Cl-, Na+ and Ca2+,the sum concentration of them accounted 79% and 80% for the TWSI in PM2.5 and TSP respectively. The existence of these ions may form as:NH4HSO4 and (NH4) 2SO4, NH4NO3, CaSO4, Ca (NO3)2,CaCl2, MgCl2, NaCl, KNO3 and K2SO4. In spring, there was NaNO3 resulting from clorine deplacing reaction.The analysis of pH and C/A showed that, generally, there was acidic pollution of atmospheric environment in the region of Xiaoyangshan Isle on the East China Sea in all of the year. This may be resulted from the pollution of SO2 and NOx transformed to SO42-and NO3- through heterogeneous reaction on the surface of mineral aerosol, such as CaCO3.These productions will further react with NaCl in sea salt, which leaded to chlorine deficiency. This region had been influenced by fossil fuel combustion emissions transporated from Yangtze River Delta area as the correlation coefficients of nss-SO42- and BC were above 0.55 other than summer, while the slope was close to 0.07.excess K/BC showed that the biomass burning contribution to K and BC was greater than that of fossil fuel for PM2.5. The correlation coefficients of BC in TSP between Shanghai and Xiaoyangshan Isle in spring and winter were 0.66 and 0.83,indicating that the influence of costal city was significant there under the condition of air mass movement from continent. With Al as reference, element enrichment factor (EF) analysis showed that the pollution of elements on Xiaoyangshan Isle of East China Sea was similar to that of urban, which further reflected the continental characteristics of atmospheric aerosl there.The analysis of source released that the total contribution of crust and sea salt to PM25 and TSP was only 9% and 19.4%, while the average concentration of mass concentration, the major ions and elements in aerosol were maximum under the wind direction of WNW or NW. That illustrated the continental source and human activity may be more important sources for atmospheric aerosols in this area. And during the sampling period,74% days were affected by air mass from continent and the concentration of particle was highest on this condition in any season. Atmospheric aerosols may impact on the coastal ecosystems and regional climate through dry deposition.更多还原