【作者】 沈小静；

【导师】 秦大河； 孙俊英；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2012， 博士

【摘要】 大气气溶胶对气候和环境的影响日益彰显，了解气溶胶的粒径大小、谱分布、浓度及化学组分等信息，对于评估其辐射强迫至关重要，同时也为治理大气污染提供依据。泰山（1534m a.s.l）位于我国东部，山顶受局地污染源影响较小，其大气成分可以代表华东区域大气的背景状况。本研究自2010年7月至2011年12月底在泰山山顶开展了干状态下（相对湿度<40%）PM2.5颗粒物理化和光学特性的观测，观测项目包括数谱分布、散射系数和黑碳（BC）质量浓度，并在加强观测时期获得了气溶胶化学组分信息和环境大气的分级采样。观测期间获得的核模态（3-25nm）、爱根核模态(25^-100nm)、积聚模态(100^-1000nm)和总颗粒物（PM2.5）数浓度平均值分别为1950、5075、3715和10740cm^-3。颗粒物数浓度接近华北上甸子区域本底站的浓度水平，但是远高于我国全球本底站瓦里关、北欧森林和高山等背景地区的颗粒物数浓度。气溶胶数谱分布有明显的季节变化和日变化，主要是受光化学反应、边界层变化、长距离输送和气象条件等因素共同影响。后向轨迹和潜在源贡献解析（PSCF）都表明泰山大气的污染物主要来自南方的气团，而西北方向多为干洁的大气。泰山新粒子生成事件的发生频率约占观测天数的40%。春季发生频率最高，夏季最低。对于增长过程连续的新粒子生成事件计算其成核速率平均值为4.0±3.7cm^-3s^-1，核模态数浓度的净增长率为2.6±2.2cm^-3s^-1,由碰并造成核模态数浓度损失的速率为1.4±1.8cm^-3s^-1，增长速率的平均值6.1±2.5nm h^-1。新粒子生成事件的增长过程对于大气气溶胶化学组分、光学特性、云凝结核和吸湿性参数都有重要的影响，是泰山大气二次气溶胶的主要来源之一。观测获得了泰山大气气溶胶分别在光波长450nm、550nm和700nm的散射系数和后向散射系数。散射系数的平均值分别是180.0（450nm），142.9（550nm）和101.2Mm^-1（700nm），后向散射系数平均值分别是20.3（450nm）,16.7（550nm）和14.7Mm^-1（550nm）。吸收系数平均值13.0Mm^-1。单次散射反照率为0.88，半球后向散射比为0.14， ngstr m指数为1.40。散射系数和吸收系数有明显的季节变化和日变化，主要受气象条件、边界层活动和长距离传输影响。利用MIE模型评估了不同化学组分对于气溶胶光学特性的贡献，发现硫酸盐对散射特性贡献最大，其次是有机物和硝酸盐。基于气溶胶光学平衡模型“二组分”假设（气溶胶由光吸收物质和非吸收物质组成）和修正的积分MIE模型进行光学闭合实验。考虑干状态下气溶胶完全内混和外混的极端条件，模拟得到的散射系数与实测值误差在10%以内，后向散射系数与实测值误差在3%以内。采用Monte Carlo模拟方法，评估得到由实验数据和模型假设的不确定性给气溶胶光学模型的最终输出结果带来的不确定性是8%。在允许的不确定性范围内，闭合结果表明散射系数有78%，后向散射系数80%以上都在该范围内。对于不同类型的气溶胶，“新鲜”的气溶胶，其混合状态更接近外混；“老化”的气溶胶接近内混状态。更多还原

【Abstract】 The atmospheric aerosols play an important role in air quality deterioration and climatechange. The particle size, size distribution, concentration and chemical component will helpto evaluate the aerosol radiative forcing and provide information for taking air controlregulation as well. Therefore, the study of the aerosol characteristics is a key point in thisfield. Mt. Tai （the summit of1534m a.s.l） located in Eastern China, which was slightlyaffected by the local pollution and could be representative for the regional background. Themeasurement was conducted at Mt. Tai from July2010to Dec2011. All the instrumentsconnected to splitter with a PM2.5inlet and autocycled drier system to keep the relativehumidity of aerosol samples lower than40%. The particle number size distribution （PNSD）,together with the aerosol scattering and absorption information were derived by differentinstruments. Chemical component measurement and size segregated sampling wereperformed during the intensive period.The average number concentration of nucleation mode （3-25nm）, Aitken mode (25^-100nm), accumulation mode (100^-1000nm) and particle number concentration of PM2.5was1950,5075,3715and10740cm^-3. The number concentration was quite close to those atShangdianzi regional background station in North China Plain, but higher than those in theglobal regional station in China, Waliguan and background stations abroad, like the borealforest and mountain site. The particle number concentration had noticeable seasonal anddiurnal variation, which could be contributed to the gas to particle reactions in the daytime,the development of boundary layer, meteorological factors, as well as the long rangetransportation. The air mass originating from south resulted in the pollutants accumulatingand northwesterly air mass favored the increase of the nucleation mode particles.NPF event were observed on40%of the measurement days, with the frequency as highas that in Beijing urban and rural environment. It occurred most frequently in spring and leastin summer. The mean formation rate was4.0±3.7cm^-3s^-1, with the net increase rate ofnucleation mode particles,2.6±2.2cm^-3s^-1and the loss due to coagulation,1.4±1.8cm^-3s^-1.The mean growth rate was6.1±2.5nm h^-1. The case study showed classical NPF eventsenhanced the aerosol mass concentration, scattering coefficient, cloud condensation nucleinumber concentration and hygroscopic parameter.The mean scattering coefficient at different wavelength was180.0（450nm）,142.9（550nm） and101.2（700nm） Mm^-1and the backscattering coefficient was20.3（450nm）,16.7 （550nm） and14.7（700nm） Mm^-1, respectively. The mean value of absorption coefficientwas13.0Mm^-1. The other information including the single scattering albedo,hemispheric-back scattering fraction and ngstr m exponent were also reported. They were0.88,0.14and1.40, respectively. The optical properties were affected by the surface wind,long range transportation and the development of boundary layer. They also had clearlyseasonal and diurnal variations. Mie model was used to evaluate the effect of chemicalcomponent on the aerosol optical properties. The result showed that the sulfate contributedmost to the extinction and scattering and then came to the particle organic matter and nitrate.Based on the two-component optical equilibrium aerosol mode （absorption andnon-absorption component） and MIE simulations, the optical closure experiment wasperformed. Two extremely mixing states, internal and external, were considered in the model.The result showed that the simulated scattering and backscattering coefficient were quiteclose to those measured, with the difference smaller than10%and3%, respectively. MonteCarlo uncertainty simulation had been done for the optical closure and gave the uncertaintyof MIE model and it was8%. Considering all the possible uncertainties, the simulatedparameters at two extreme states covered78%scattering data and80%backscattering data.The case studies showed that there was more BC in external mixing state for the freshparticles, but more in internal mixing state for the aged particle.更多还原