【作者】 张艳；

【导师】 陈立民；

【作者基本信息】 复旦大学 ， 环境科学， 2007， 博士

【摘要】 氮素对于海洋生态系统的物质循环意义重大。许多陆源排放区靠近海岸,其释放的大气含氮污染物通过扩散稀释、化学转化和长距离传输,最终将沉降到开阔的海洋表面。为了了解陆源大气含氮物质对中国东部海域大气物质含量的影响以及氮素输入的贡献,本文采用外场定点观测和区域数值模拟相结合的手段,调查了典型海域大气污染特征和氮沉降通量,进一步研究了区域大气含氮物质的长距离输送通量、浓度和沉降通量的时空分布规律。主要研究内容和结果如下。首先,结合外场观测资料和污染过程模拟结果,对典型海域大气污染特征、粒径分布、污染物来源和氮沉降通量的研究表明:2006年5月至6月观测试验期间,大气含氮气溶胶水溶性离子NO₃^-和NH₄⁺的平均浓度分别为10.4μg/m³和5.1μg/m³,观测期间其峰值分别达到了38.5μg/m³和20.8μg/m³;粒径分布显示,NO₃^-和NH₄⁺存在明显的细颗粒态向粗颗粒态转移,通过离子存在形式和海盐贡献分析表明,是其气体前体物在高湿度条件下与矿尘气溶胶和海盐气溶胶发生复相反应的结果;梯度法观测氮沉降的结果显示,NO₃^-和NH₄⁺的干沉降速率分别为1.23 cm/s和1.15 cm/s,总的氮沉降通量中,N-NH₄⁺贡献了70%左右;源解析表明,海洋大气含氮气溶胶浓度的变化直接受不同方向气流的影响,高浓度污染日是由于持续的陆源污染物送输和特殊的海洋天气条件共同造成的。其次,利用区域气象模式（MM5）和区域化学传输模式（CMAQ）详细研究了2004年1、4、7和10月四个典型月大气含氮物质的输送通量特征,以及区域海洋大气含氮物质浓度的时空分布,结果表明:冬季1月份气象条件最有利于污染物质从中国大陆向海洋的传输,一次污染物氮氧化物的水平输送通量高值区主要集中在排放通量较高的长三角一带,NH₃的水平输送通量的高值区集中在华东地区的北部,而二次污染物HNO₃、NO₃^-和NH₄⁺的输送通量的高值区范围分布较广,且在一定范围内随着高度的增加输送通量增加;随着离岸距离越远,纬向输送通量越小,离岸50 km至100 km之间变化最大,200 km处输送通量分布趋于均匀;季节对比发现,7月份物质的纬向输送可以达到较高的高度,平均比1月份抬升1000米;受上游输送通量的直接影响,海域大气含氮物质的浓度分布呈明显的季节变化。1月份浓度较高,局部地区的NO_x月均浓度达到了15-100 n molm^-3,NH3的月均浓度达到60-500 n mol/m³。而NO₃^-和NH₄⁺的月均浓度也达到了80 n mol/m³和200 n mol/m³,且黄海海域含氮物质浓度较高,而东部海域东南地区相对较小;浓度分布表明,以（NH₄）₂SO₄形式存在的铵根在各个季节都能输送到较远的海域,而NH₄NO₃的输送主要集中在近海海域。第三,海表动态粗糙度方案对大气干沉降影响的敏感性分析表明,海表粗糙度对NH₃和HNO₃气体干沉积速率的影响最明显,区域平均结果显示,海表粗糙度的变化范围位于0.01-0.03 cm时,湍流层阻力R_a降低了10%以上,而粘附层阻力R_b下降了大约5%左右,对干沉降速率的改变范围在5%-19%;整个海域统计来看,模拟得到的HNO₃的干沉积速率在1月、4月、7月和10月分别为0.51 cm/s、0.58 cm/s、0.65 cm/s和0.79 cm/s。NH₃的干沉积速率与HNO₃接近。最后,利用改进了沉降模块的区域模式研究了2004年区域大气氮沉降通量的时空分布规律及其对海洋生态系统初级生产力的潜在贡献:与大气含氮物质输送通量场和浓度场相对应,1月份东部海域大气氮沉降量最大,为7.4万吨。整个东部海域的年氮沉降量为49.8万吨,大气干沉降约占20%,但大气干湿比例随着离岸距离有明显的梯度变化,部分近海海域大气干沉降约占总沉降的70%以上;各组分中,N-NH₄⁺贡献最大,占总沉降的60%以上;不同区域源排放对东部海域大气氮沉降的贡献率研究表明,华东以外区域的贡献占44%,而华东内的临海长三角地区的贡献也占了44%左右。不同海域大气氮沉降统计显示,大气沉降和陆源氨氮输入是可比的,在氨氮输入中占39%-88%不等。东部海域全年氮沉降量换算成海洋初级生产力指标后,平均为100-200 m mol C/m²/year。更多还原

【Abstract】 Nitrogen compounds are very important nutrients for marine ecosystem.Since many anthropogenic source regions are close to coasts,there is a significant amounts of atmospheric pollutants containing nitrogen transported over and deposited into ocean.To understand the impacts of atmospheric nitrogen input into the East China sea,the magnitude and seasonality of atmospheric nitrogen compounds’ transport flux,concentration and deposition flux has been studies by the field mesurements and numeric simulation.The major contents and conclusions in the study are shown below.Field measurements of aerosols were conducted at typical site in the East China Sea.Ion composition,size distribution,source and dry deposition of NO₃^--N and NH₄⁺-N of TSP were studied.NO₃^- and NH₄⁺ reached average concentrations of 10.4 and 5.1μg/m3,respectively,and as high as 38.5 and 22.8μg/m³ on a sea fog day. Size-distribution analysis showed evident shifting of nitrate and ammonium to coarse mode.That might have been the result of reactions with dust aerosols and sea salt aerosols by statistic analysis and pollution process simulation.Also the Micrometeorological Concentration Gradient Method（MCGM）was used to estimate the dry deposition flux of nitrogen.The mean dry deposition velocities of NO₃^- and NH₄⁺ were estimated to be 1.15 cm/s and 1.23 cm/s,respectively.For observed nitrogen deposition in the aerosol,N-NH₄⁺ deposition contributed about 70%.The air mass back-trajectory analysis showed the coastal sea region has been seriously influenced by terrestrially derived materials carried on the westerly terrestrial airflow.The meteorological conditions and pollutants concentrations have been simulated by the middle scale meteorological model（MM5）and chemical transport model （CMAQ）.The atmospheric circulation and synoptic system in the winter and the autumn were in favor of the transport of nitrogen compounds from the terrestrial to East China Sea.As the primary pollutants,the peak transport fluxes for NO_x and NH₃ occurred in the Yangzte delta and the north part of East China corresponding to their source region.However,that is different for the secondary pollutants of HNO₃,NO₃^-and NH₄⁺,transport fluxes of which were more evenly distributed in the model domain.Lateral transport in different section planes showed the variation with fetch, which is larger over fetches of up between 50 km and 100 km.And the transport flux in July could reach up to higher vertical layer,1000 m higher than that in January. There also were obvious seasonal and spatial variations in the concentration of atmospheric nitrogen compounds.In January,NO_x,NH₃,NO₃^- and NH₄⁺ in the north part of East China Sea reached higher concentrations of 15-100nmol/m³,60-500 nmol/m³,80 nmol/m³ and 100 nmol/m³,respectively.And（NH₄）₂SO₄ were found to be suitable for transport to more remote sea area than NH₄NO₃.The impacts of the sea roughness length on the dry deposition velocities have been studies.The dry deposition velocities of NH₃ and HNO₃ have been influenced in the most degree than the other nitrogen compounds.Totally,the sea roughness length in model domain varied in 0.01 cm-0.06cm,the turbulence resistance R_a and sub-layer resistance R_b decreased above 10%and 5%,respectively.By statistics,the mean dry deposition velocities（V_d）of HNO₃ were 0.51 cm/s in January,0.58 in April,0.65 cm/s in July and 0.79 cm/s in October.The V_d for NH₃ was very close to the one of HNO₃.By comparison with the other studies and the measure result in Yangshan isel, the dry deposition velocity estimated considering dynamic sea roughness length was proved to be more precise.The atmospheric nitrogen loads to the East China sea have been estimated by modified regional model.The nitrogen deposition flux was the largest in January due to higher transport fluxes and concentrations of atmospheric nitrogen compounds.Dry deposition accounted for 20%of the total deposition in the full ocean area.However, there were regional gradient in the ratios of the dry to wet deposition.The dry deposition is 2.5 times as high as the wet deposition.Pollutants from the Yangzte river delta source region have contributed 44%of the total deposition roughly,which is comparable with that contribution by the region outside East China.The atmospheric nitrogen inputs into the China sea were shown to be comparable in size to the other terrestrial nitrogen inputs such as the riverine transport etc.Averagely,the deposition of atmospheric nitrogen has the potential to promote primary productivity of 100-200 m mol C/m²/year for the East China Sea.更多还原