【作者】 熊鹰；

【导师】 周家斌；

【作者基本信息】 武汉理工大学 ， 环境科学与工程， 2017， 硕士

【摘要】 大气细颗粒物(PM_2.5)对于全球气候、区域环境质量和人体健康有着重要的影响。有机物作为大气PM_2.5的重要组成部分,已占到PM_2.5质量的1/3¹/2,它通过增强散射和反射太阳光引起辐射强迫变化,进而导致大气能见度下降。目前针对大气颗粒有机物的研究十分有限,据此,本文选取大气PM_2.5中有机物作为研究对象,在武汉市三个典型地区（工业区、交通区、植物园）开展了为期一年的PM_2.5样品采集。分析了武汉市大气PM_2.5中有机物的化学组成及其污染分布特征,并结合化学质量平衡（CMB）模型确定了大气有机气溶胶的主要来源。有机物和二次无机离子是武汉大气PM_2.5中最重要的两类化学组分,两者之和分别占工业区、交通区以及植物园PM_2.5质量的47.1%,56.9%和57.2%。武汉市大气PM_2.5中化学组分的浓度呈现出明显的时空分布特征。其中,硫酸根、硝酸根和有机碳在春季三个采样点差异最大,其次是夏季和秋季。工业区排放的碳质气溶胶是导致三个采样点PM_2.5化学组分差异的主要原因。大气PM_2.5样品中共检测到颗粒有机物125种,包括27种多环芳烃、31种正构烷烃、23种藿烷甾烷、32种有机酸以及12种脱水单糖。其中多环芳烃的浓度在冬季主要受机动车尾气排放的影响;正构烷烃的碳优势指数（1.1±0.2）接近1以及C₂₃、C₂₄的主峰碳特征表明武汉市大气有机气溶胶主要受人为污染源排放的影响;化石燃料燃烧的示踪物藿烷甾烷类在交通区浓度最高,达到了13.0±8.4 ng/m³,反映出机动车排放的污染特征;而生物质燃烧的示踪物左旋葡聚糖在秋季出现的极端值（2794.3 ng/m³）也说明了武汉市秋季大范围生物质燃烧的污染现象。根据已定量化合物的日变化特征,结合气团后向轨迹分析和卫星火点数据,对2011年秋季武汉市出现的PM_2.5极端污染事件进行了成因分析。结果表明,此次污染事件主要是由于安徽、江苏、河南等地大范围秸秆燃烧产生的污染物经过远距离传输到达武汉而导致的。此外,不利的大气扩散条件（高湿>80%,低风速和低压）引起污染物在近地表发生累积,进一步加重了大气污染过程。此外,武汉市大气PM_2.5中有机碳（OC）的来源主要有:机动车排放（38.1%±8.3%）,二次有机碳（37.9%±7.8%）,燃煤（7.0%±6.2%）,肉类烹饪（3.0%±1.6%）,生物质燃烧（3.0%±1.0%）以及植物碎屑（0.8%±0.6%）,这6类污染源合计贡献了OC年均浓度的89.7%±10.2%。二次无机离子是PM_2.5最大的污染源,其对PM_2.5质量的贡献为24.2%±3.1%;机动车排放是第二大污染源,贡献了PM_2.5质量的20.0%±4.0%。矿物尘在春季对三个采样点PM_2.5表现出均一的贡献,这与区域沙尘气团的传输有关。总体而言,一次污染源和二次污染源累计贡献了PM_2.5质量浓度的83.4%±9.8%。三个采样点源解析结果的对比分析表明:武汉市PM_2.5的本地排放源中,机动车尾气排放对交通区影响很大;燃煤、矿物尘以及工业排放对工业区影响最大;而PM_2.5的区域污染源如二次硫酸盐、二次硝酸盐和二次铵盐在三个典型地区表现出一致的贡献。更多还原

【Abstract】 Fine particulate matter(PM_2.5)has been shown to have pronounced effects on human health,regional air quality,and global climate.Particulate organic matter is the major constituent of PM_2.5,accounting for approximately 1/3¹/2 PM_2.5 mass.It has been reported that organic matter could change radiation intensity by increasing scatter and reflection of light,resulting in atmospheric visibility reduction.Nevertheless,the temporal and spatial variation of organic matter was rarely investigated in China.Therefore,the present study aims to measure the detailed chemical composition of organic species in PM_2.5 and study the spatiotemporal variations of sources contributing to organic carbon.PM_2.5 samples were collected simultaneously at three sites in Wuhan in industrial area（ID）,downtown Wuhan（DT）,and Wuhan botanical gardens（BG）.The major constituents of PM_2.5 were found to be organic matter and secondary inorganic ions,totally explaining 47.1%、56.9%,and 57.2%of PM_2.5 mass at ID、DT and BG site,respectively.The concentration of major constituents of PM_2.5.5 varied seasonally across all sites;specifically,sulfate,nitrate and organic carbon varied most strongly during spring,followed by summer and fall.Organic carbon varied the most across sites for all seasons,which is attributable to large differences in local industrial emissions.A total of 125 organic species in PM_2.5 were identified and quantified,including27 polycyclic aromatic hydrocarbons（PAHs）,31 n-alkanes,23 hopanes and steranes,32 fatty acids and 12 monosaccharide.The highest concentration of PAHs observing in winter could be ascribed to cold-ignition of vehicles.The average CPI value（1.1±0.2）and relatively lower C_max(C₂₃,C₂₄)for n-alkanes indicate the predominance of anthropogenic sources in Wuhan.Hopanes and steranes acted as molecular markers and are mainly produced by fossil fuel combustion.The highest annual concentration of hopanes and steranes was found at DT site（13.0±8.4 ng/m³）,confirming the significant vehicle emissions at this site.Levoglucosan can be utilized as a molecular tracer for biomass burning.Extremely high values of levoglucosan（the maximum value:2794.3 ng/m³）were observed at all sites,and 72h backward trajectory analysis revealed that regional-range transport（from Jiangsu、Anhui and Henan）of biomass burning emissions mixed with locally produced pollutants could be the main cause of serious haze pollution event in fall of Wuhan.Using the molecular markers-CMB model,the contributions of primary sources to organic carbon（OC）in PM_2.5 were calculated.The major primary sources contributing to OC were vehicle emissions（38.1%±8.3%）,coal combustion（7.0%±6.2%）,meat cooking（3.0%±1.6%）,biomass burning（3.0%±1.0%）,and vegetative detritus（0.8%±0.6%）.Secondary organic carbon（SOC）was estimated based on EC-tracer method,and the percentage of SOC to total OC varied from16.2%⁶3.7%with an average of 37.9%.Additionally,the contributions of primary sources plus secondary inorganic ions including sulfate,nitrate,and ammonium,accounted for 83.4%±9.8%of PM_2.5 mass on a yearly average basis over all site.Secondary inorganic ions contributed the most to PM_2.5 mass,accounting for 24.2%±3.1%of PM_2.5 mass.Vehicle emissions were the second largest contributors to PM_2.5 mass,averaging 25.5±11.6μg/m^-3 and accounting for 20.0%±4.0%of PM_2.5 mass.Mineral dust was the next major contributor to PM_2.5(average 16.8±9.6μg/m^-3)and have homogenous concentrations across the sites during springtime due to regional dust storms,but had much higher concentration at ID during the summer and fall.All these sources had large spatial variations across the three sampling sites.Vehicle emissions had the largest impact at DT,coal combustion,mineral dust and industrial emissions had the largest impact at ID.In contrast,regional sources,such as secondary sulfate,nitrate and ammonium contributed equally to the PM_2.5.5 mass in sub-areas of Wuhan.更多还原