【作者】 王哲；

【导师】 王文兴；

【作者基本信息】 山东大学 ， 环境工程， 2011， 博士

【摘要】 大气气溶胶是我国最主要的空气污染物之一,而碳质气溶胶是其中的主要组分。大气碳质气溶胶对全球气候变化、太阳辐射平衡、温室效应、大气能见度和人体健康等方面都有重要的影响。由于华北地区能源消耗强度和气溶胶排放强度较大,导致此区域是全球气溶胶浓度最高的地区之一。因此全面阐明我国高污染条件下大气气溶胶和碳质气溶胶的污染现状和变化特征,并了解其来源和形成机制,对制定控制对策具有重要意义。本研究选择中国气溶胶污染较重的典型地区,在济南、青岛、淄博和枣庄等典型城市分别设立4个城区和1个郊区(济南苗圃)观测点,并在泰山建立高山大气观测站,对大气气溶胶和碳质气溶胶进行了连续观测。对区域范围内城市及边界层大气气溶胶和碳质气溶胶的污染特征和时空分布进行了研究,探讨了其传输和来源,并对二次有机气溶胶(SOA)的含量、形成和变化特征进行了研究。此外,本研究还考察了云雾对碳质气溶胶的清除作用和液相SOA生成过程,研究了气溶胶的云凝结核(CCN)特性和SOA对气溶胶CCN活性的影响,并系统地测定了NaCl(?)内米颗粒的形状因子。济南市区、济南郊区、青岛、淄博、枣庄和泰山六个观测点PM2.5、有机碳(OC)和元素碳(EC)浓度均值范围分别为44.7-191.0μg m-3、15.93-38.03μgm-3和1.31-5.03μg m-3。PM2.5和碳质气溶胶浓度都高于国内外其它城市和背景站观测浓度,而且济南城区长期观测结果显示PM2.5和碳质气溶胶浓度都呈现缓慢增长趋势。PM2.5和碳质气溶胶浓度都表现出明显的季节变化,冬春季较高而夏季最低,表明燃煤排放仍然是我国北方地区PM2.5和碳质气溶胶的主要来源之一。本研究在华北地区首次连续观测了边界层顶大气半挥发性有机碳(SVOC),结果显示,春、夏季平均浓度分别为6.26、13.33μg m-3,占总有机碳(TOC)浓度的51%和72%,说明半挥发性有机气溶胶是此区域边界层内大气有机气溶胶中的主要组成。六个观测点有机气溶胶占PM2.5质量浓度的平均比例范围在19.9-66.0%,反映出区域范围内有机污染物排放量较大,碳质气溶胶污染较重。对碳质气溶胶的日变化特征分析发现,城市地区黑碳(BC)浓度主要受人为活动、交通源排放和气象条件的影响,而泰山地区碳质气溶胶浓度主要受传输和二次生成来源影响,并且在传输过程中混合了多种不同来源,包括燃煤排放、交通排放、生物质燃烧等。利用PCA和HCA分析发现泰山春、夏季高浓度的NVOC和EC主要来自于边界层内污染物的传输,而来自自由对流层的干净气团中碳质气溶胶浓度较低。高浓度的SVOC与云雾过程相关,并且由光化学氧化和液相反应生成的SOA在夏季都有所增强。研究还证实,我国华北地区生物质燃烧和韩国地区污染物的排放对我国华北地区和东亚地区碳质气溶胶浓度都有明显的影响。此外,还得到区域边界层顶碳质气溶胶的背景浓度,NVOC为2.13±1.05μg m-3,EC为0.43±0.29μgm-3,而SVOC在2.40-6.80μgm-3范围内。分别利用EC约束示踪法和改进的多元回归方法对典型城市和泰山站大气中二次有机气溶胶浓度进行了测算,结果显示,各城市大气中二次有机碳(SOC)浓度范围为8.25-23.46μg m-3,占TOC总量的40.13-58.91%,枣庄浓度最高而青岛最低。泰山春、夏季总SOC的浓度分别为8.19和13.26μgm-3,占TOC总量的57.3%和71.2%,其中半挥发性二次有机碳(SV-SOC)占总SOC的60.4%和74.9%。结果表明观测期间有大量的SOA形成,也反映出华北地区边界层内较高的SOA通量和前体物排放量。对SOC和光化学寿命关系分析发现,NV-SOC和SV-SOC与光化学寿命关系不同且两者均表现出明显的季节差异。春季NV-SOC与光化学寿命呈正相关关系,而SV-SOC则表现出单峰形态,说明随光化学寿命的增加NV-SOC不断的生成,而SV-SOC则受气态前体物生成和向更低挥发性组分转化的动态平衡控制。夏季更加老化的气团中NV-SOC与光化学寿命的关系不明显,而SV-SOC则继续向不挥发性组分转化而表现出浓度下降的趋势。泰山观测期间发现云雾对NVOC和EC有明显的清除作用,清除效率范围分别为0.33-0.93和0.62-0.94。与不挥发组分变化相反,SVOC浓度在云雾过程中表现出上升趋势,净增长浓度范围在3.67到19.04μgm-3,说明有大量的SVOC在云雾过程中生成和增长。利用云雾-气溶胶作用模型获得NVOC和EC的清除系数常数KNVOC和KEC,以及SVOC的生成速率常数JSVOC和汇机制常数SSVOC。KNVOC夏季低而春季高,范围为0.07-0.55 h-1,春、夏季平均值分别为0.16和0.11 h-1。KEC范围为0.11-0.90 h-1,与KNVOC表现出相似的季节变化,但大部分KEC值都高于KNVOC,说明EC颗粒在传输过程中与吸湿性颗粒(硫酸盐、硝酸盐等)发生了内部混合。JSVOC范围为0.09-1.39 h-1,春、夏季平均值分别为0.88和0.45 h-1,其中夏季波动相对较大。SSVOC表现出与JSVOC同样的季节变化,范围为0.001-1.07 h-1。SVOC在云雾过程中的增长速率受已存在气溶胶浓度、前体物浓度、氧化剂浓度和汇机制的共同影响,SVOC的增长曲线主要取决于源和汇机制的相互竞争。本研究还利用CCNC仪器研究了NaCl和(NH4)2SO4颗粒的CCN活性,发现在相同超饱和度下NaCl的临界活性直径小于(NH4)2S04,表明气溶胶粒子的CCN活性取决于其粒径和化学成分的共同作用。利用烟雾箱研究了由α-pinene和isoprene生成的SOA对颗粒CCN性质的影响,结果发现随SOA在(NH4)2SO4颗粒上的生成,CCN活性有了较大提高。不同来源和种类的SOA对CCN活性影响不同,由α-pinene生成的SOA比isoprene生成的SOA对颗粒CCN活性增强作用更加显著。而随有机物体积分数的升高,SOA-(NH4)2SO4内混粒子的临界超饱和度也随之上升。此外,本研究利用Flow tube-DMA-CCNC系统测得干燥速率在5.5±0.9到101±3 RH s-1范围内的NaCl颗粒的形状因子χ在1.02到1.26之间。NaCl形状因子χ受粒径和干燥速率的共同影响,相同粒径下,χ随干燥速率的增加而降低,而相同干燥速率下,χ在35-40nm粒径最高。NaCl形状因子χ随粒径和干燥速率的变化主要取决于颗粒相水的扩散运动和NaCl单体运动的特征时间的相互竞争,以及体系大小的影响。更多还原

【Abstract】 Atmospheric aerosol is one of the major pollutants in the atmosphere, having significant effects on air quality and human health. Carbonaceous aerosols are known to contribute significantly to the atmospheric fine particles, and not only have crucial impacts on human health and environment, but also play important roles on climate change, radiation balance, greenhouse effect, and visibility. Due to the large energy consumption and emission, the North China is among the areas with the highest aerosol concentrations in the world. Thus, the study on physical and chemical characteristics of carbonaceous aerosols, and understanding of the sources and formation mechanism of carbonaceous aerosols in this region is therefore needed, which clould further promote the control strategy of government.In this work, representative areas were chosen to conduct measurement campaigns on atmospheric carbonaceous aerosols. The measurement studies were performed at four urban sites (Jinan, Qingdao, Zibo, Zaozhuang), one suburban site, and one mountain site (Mount Tai). In the present study, we report the concentrations and temporal variations of fine particles and carbonaceous species in urban cities and in the planetary boundary layer (PBL), investigate the sources and processes that affect the variation of carbonaceous aerosols, examine the cloud scavenging of carbonaceous aerosols and SVOC formation through aqueous-phase reactions in clouds. We also study the cloud condensation nuclei (CCN) activity of both inorganic and organic aerosols, and quantitatively determine the dynamic shaper factor of NaCl nanoparticles.The results showed that the concentrations of PM2.5, OC and EC in Jinan, Qingdao, Zibo and Zaozhuang were much higher than other urban cities in the world, and the concentrations at Mt. Tai were also higher than other background and mountain sites in the world, suggesting the serious atmospheric pollution in this region. The concentrations of PM2.5 and carbonaceous species exhibited clear seasonal variation, with higher concentration in winter and spring but lowest concentration in summer. The semi-volatile organic carbon (SVOC) was measured at Mt. Tai for the first time, and its concentration accounted for 51% and 72% of total OC in spring and summer, respectively, suggesting the predominance of semi-volatile species in organic aerosol in this region. The contribution of organic aerosol to PM2.5 mass in six sites ranged from 19.9% to 66.0%, indicating the large emission and serious pollution of carbonaceous aerosols. The long-term observation in Jinan also indicated that the concentrations of PM2.5 and carbonaceous species all exhibited a slightly increasing trend, highlighting the significance of aerosol pollution control in this region.The diurnal variation of carbonaceous species suggested that the BC concentration in urban area was related to the human activities, traffic emission and meterological parameters, whereas the carbonaceous concentrations at Mt. Tai were dominated by transport and secondary formation. The results suggested the combined sources for the transported aerosols at Mt. Tai, including coal combustion, traffic exhaust, biomass burning and photochemical production. Source analysis based on PCA and HCA indicated that high carbonaceous concentrations were dominated by transport of PBL pollutions in both seasons, and clean air masses from the free troposphere provided the general background condition with 2.13±1.05μg m-3 of NVOC,0.43±0.29μg m-3 of EC and 2.40 to 6.80μg m-3 of SVOC in the study area. Besides the biomass burning in north China, the influence of emission from Korea was observed during the campaigns, and was thought to partially contribute to the regional carbonaceous aerosol budget. Increased SVOC was associated with both cloud processing and photochemical production.The constrained EC-tracer and multiple regression method were used to estimate SOC formation at urban areas and Mt. Tai. The average concentration of SOC at four cities ranged from 8.25 to 23.46μg m-3, accounting for 40.13% to 58.19% of total OC. The average total SOC concentrations at Mt. Tai were 8.19 and 13.26 ug m-3 in spring and summer, respectively, accounting for 57.3% and 71.2% of TOC. The contributions of semi-volatile secondary organic carbon (SV-SOC) to SOC were 60.4% and 74.9% in spring and summer, respectively. The results indicated strong SOA formation during campaigns and high SOA loading in the PBL of the North China Plain. An examination of SOC with photochemical age reveals different relationships of non-volatile and semi-volatile SOC with age and also a different seasonal dependence. NV-SOC increased with photochemical age in spring, while SV-SOC exhibited a mono-peak pattern. These results indicated continuing formation of NV-SOC and SV-SOC being determined by the dynamic equilibrium between formation from gas-phase precursors and conversion to the non-volatile phase in spring. This dependence was not significant in more aged air masses observed in summer, revealing that the aerosol had been fully processed before being transported to Mt. Tai. The clear scavenging of NVOC and EC by clouds was observed at Mt. Tai, and the scavenging efficiencies of NVOC and EC were in the range of 0.33-0.93 and 0.62-0.94, respectively. In contrast to the non-volatile species, SVOC concentration showed increasing trend during clouds, with net increase ranged from 3.67 to 19.04μg m-3 for all cloud events, suggesting in-cloud formation of semi-volatile organic species. A mass balance model was proposed to quantify the scavenging coefficients for NVOC, EC and formation rate of SVOC during clouds. The derived scavenging coefficient constant for NVOC (KNVOC) varied from 0.07 to 0.55 h-1, with averages of 0.16 and 0.11 h-1 in spring and summer, respectively. The scavenging coefficient constant of EC (KEC) ranged from 0.11 to 0.90 h-1, and was higher than that of NVOC, implying internal mixing of EC with more hygroscopic species. The formation rate constant (JSVOC) and sink constant (SSVOC) of SVOC ranged from 0.09 to 1.39 h-1 and 0.001 to 1.07 h-1, respectively. The results suggest that the SVOC growth rate in cloud processing depends on both pre-existing aerosol concentration and sink mechanism, and the growth curve is determined by the competing formation and sink processes.The CCN activity of NaCl and (NH4)2SO4 particles was studied by using CCNC, and the results showed that the critical diameter of NaCl was much smaller than that of (NH4)2SO4 under the same supersaturation. The CCN activity of particles depends on both size distribution and chemical composition of particles. The SOA formed from a-pinene and isoprene in Environmental Chamber was studied, and the CCN activity was remarkably altered by SOA formed on seed particles (i.e., (NH4)2SO4). The SOA formed from a-pinene increased the CCN activity of particles more significantly than that of isoprene, suggesting that the impacts of SOA on CCN property of particles were related to its source and composition. The results also indicated that the critical supersaturation was increased for greater SOA volume fraction. The dynamic shape factor x of NaCl nanoparticles was investigated with a Flow tube-DMA-CCNC system. The drying rate at efflorescence RH was quantified and varied from 5.5±0.9 to 101±3 RH s-1, and the derived x ranged from 1.02 to 1.26. The dynamic shape factors of NaCl particles depended on both particle size and drying rate. For fixed particle diameter, theχvalue decreased with increasing drying rate. For fixed drying rate, a maximum occurred in x between 35-and 40-nm diameter, with a lower x from both smaller and larger particles. The dependence of x on particle size and drying rate could be attributed to the competing effects of the dominant characteristic time of particle-phase diffusion of water and diffusive movement of NaCl monomers, coupled to system size.更多还原