Knowledge Resource Center for Ecological Environment in Arid Area
| 兰州城市气溶胶谱特征及其与大气逆温的相互作用研究 | |
| 其他题名 | Atmospheric particle size distributions and their interactions with atmosphere temperature inversion in urban Lanzhou |
| 赵素平 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 余晔 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 随着经济的发展和机动车保有量的增加，城市大气污染已成为全球关注的热点问题之一。目前我国正处于经济高速发展期，中东部地区正在遭受着严重雾霾天气困扰的同时，西部地区的大气污染也不容忽视。兰州位于青藏高原、蒙古高原和黄土高原的交界处，属大陆性干旱半干旱地区，黄河穿城而过，是典型的河谷城市。由于特殊的地形及其所产生的一系列气候效应使兰州成为我国大气污染最严重的城市之一。前人关于兰州大气污染的研究主要集中在粗模态颗粒物，对亚微米粒径颗粒物数浓度特征的研究很少。本文利用电迁移率和空气动力学粒径谱仪、微波辐射计、雨滴谱仪和自动气象站等仪器的观测数据，通过主成分分析和多元对数正态分布拟合等统计方法，在分析兰州城区大气颗粒物谱特征及其主要影响因素的基础上，对新粒子生成事件、气象条件和沙尘事件对大气颗粒物谱特征的影响进行了深入分析，并探究了山峰加热对日间脱地逆温的影响以及不同粒径段颗粒物与逆温之间的相互作用，得出以下主要结论： 1）受均相核化、局地排放和扩散条件的共同影响10~50 nm粒径段颗粒物数浓度在1月、5月和8月均较高，而50~100 nm、100~1000 nm和1~10 μm 三个粒径段颗粒物数浓度在1月出现峰值。核模态颗粒物数浓度日变化特征的季节差异最显著，其在春季为三峰型（峰值分别出现在早上、中午和晚上）、夏季为单峰型（峰值出现在中午），而秋、冬季为双峰型（峰值分别出现在早上和晚上），这种变化特征反应了新粒子生成以及人类活动的影响。其它粒径段颗粒物数浓度在四季均为双峰型（峰值分别出现在早上和晚上），但是受兰州山谷城区大气边界层结构以及山谷风的转换影响，峰值出现的早晚存在明显差异，夏季早上的峰值出现在08:00时，冬季的出现在11:00时。四季大气颗粒物数谱分布几乎均为单峰型，但是冬半年的峰值粒径大于夏半年，而且冬半年爱根核模态和积聚模态颗粒物数浓度高于夏半年。冬半年粒径大于50 nm颗粒物所占比例较高主要与燃煤取暖和弱的大气扩散条件有关，而夏半年核模态颗粒物数浓度较高，与新粒子生成和增长事件在春、夏季发生的频率较高有关。 2）兰州城区40%的观测日有新粒子生成事件的发生，它们主要出现在春季和夏季，特别是5月和8月，在1月出现频率最低。而且大部分新粒子生成事件（NPF）容易发生在晴朗、干燥和大风的天气条件下。新粒子生成日，气态前体物SO2和光化学反应产物O3浓度明显高于无新粒子生成日，而一次排放的气态污染物NO2和CO浓度差异较小。此外，较低浓度的已存在颗粒物有利于兰州城区新粒子生成事件的发生。兰州城区新粒子生成和增长速率分别在2.52~22.41 cm-3 s-1和3.75~6.08 nm h-1范围内变化，这与世界上其它地区获得的结果具有较好的一致性。 3）气温、相对湿度、风速和降水对不同粒径段颗粒物数浓度的影响存在较大差异。春季，颗粒物数浓度主要受风速的影响；夏季，大气颗粒物数浓度不仅依赖于气温而且依赖于相对湿度和风速；秋季，爱根核模态和积聚模 态颗粒物对气温更为敏感。气象条件对数谱峰值粒径的影响在夏季表现的最为显著，峰值粒径分别随着气温或相对湿度的升高而显著减小或增大，春、夏季随着风速的增加峰值粒径从约70 nm减小到20 nm左右。另外，降雪对20~1000 nm和2000~10000 nm粒径段颗粒物的清除较降雨有效，而对于1000~2000 nm粒径段颗粒物，降雨的清除作用更明显。降雪的清除系数随着颗粒物粒径的变化有明显变化，且降雪能有效地减少大气中粒径大于4 μm的颗粒物。降雪和降雨对10~10000 nm粒径段颗粒物的清除系数分别为3.11×10-7 ~ 1.18×10-3 s-1和3.18×10-6 ~ 7.46×10-4 s-1。非雷暴雨能有效地清除大气中粒径小于500 nm的颗粒物，而雷暴雨对500~1000 nm粒径段颗粒物的清除作用更明显。雷暴和非雷暴雨对10~10000 nm粒径段颗粒物的清除系数分别为8.25×10-7 ~ 1.23×10-3 s-1和7.48×10-6 ~ 7.46×10-4 s-1。 4）对于不同来源的沙尘，下游城市大气颗粒物的体积中位径以及沙尘天气前后颗粒物数、表面积和体积浓度谱分布的演变存在显著差异。DS1（沙尘主要源自内蒙古中西部的沙漠区）和DS2（沙尘主要来源于塔克拉玛干沙漠及其周边地区）期间兰州城区大气颗粒物体积浓度谱两个模态的体积中位径（VMD）分别位于3.0±0.2 μm、5.0±0.1 μm（DS1）和 2.7±0.04 μm、3.8±0.03 μm（DS2）附近，可以看出不同来源沙尘其粒径存在较大差异。据此，探索了通过沙尘颗粒物的谱分布特征及其模态参数确定沙尘来源的方法。 5）利用兰州城区秋、冬季（2012年9月~2013年2月）期间大气颗粒物数浓度谱数据、气温廓线以及气象数据探索了贴地逆温和脱地逆温与大气颗粒物之间的相互作用以及山峰加热对日间脱地逆温的影响。通过分析有贴地逆温、有脱地逆温和不存在逆温三种气温廓线的出现频率以及对应的大气颗粒物平均数浓度谱分布特征，发现三类气温廓线对应的大气颗粒物数浓度谱分布特征相似，但是不同粒径段颗粒物数浓度存在较大差异。有贴地逆温存在时颗粒物数浓度最高而不存在逆温是颗粒物数浓度最低，特别是爱根核模态和积聚模态颗粒物表现的最为显著。兰州城区秋、冬季脱地和贴地逆温均通过降低大气的扩散能力使大气中爱根核模态和积聚模态颗粒物数浓度显著增加。日间脱地逆温主要受山峰加热和积聚模态颗粒物直接辐射效应的影响，而贴地逆温主要受爱根核模态和积聚模态颗粒物与逆温之间正反馈作用的影响。 |
| 英文摘要 | With the economic development and increases of vehicle numbers, urban air quality has been attracting more attention and became one of the hottest field of atmospheric environment research. In recent years, the intense haze episodes frequently occurred in economically developed regions in central or eastern China have rised intense public concern, however, air pollution is also severe in western Chinese cities, which need further research. Lanzhou (36.05oN, 103.88oE), located at the intersection of Qinghai-Tibet Plateau, the Inner Mongolian Plateau and the Loess Plateau, is a typical continental arid and semi-arid region with average elevation of 1520 m and is surrounded by mountains and hills rising to 200-600 m above the earth’s surface. Lanzhou is one of the most polluted cities in China due to its valley-shaped terrain and the related climate effects. However, previous studies on air pollution in Lanzhou mainly concentrated on coarse mode particles with less attention to characteristics of submicron particles. In this study, comprehensive observational data, including particle size distributions (PNSDs) from SMPS and APS, vertical temperature profiles from microwave radiometer, raindrop spectrum and basic meteorological data, were used to study the PNSDs and their main influencing factors by statistical methods such as principal component analysis and multivariate logarithm normal distribution, to evaluate the effects of NPF (new particle formation) events, meteorological conditions and dust events on particle size distributions, and to investigate the impact of mountain heating on elevated inversion layer and the interactions between particles in different size bins and the temperature inversions. Main conclusions are as follows: 1) The particle number concentrations in 10-50 nm were higher in January, May and August than those in other months due to synthetical effects of homogeneous nucleation, local emissions and diffusion conditions, while the highest number concentration for particles in 50-100 nm, 100-1000 nm and 1-10 μm appeared in January. Diurnal variations of the number concentrations of nucleation mode particles were significantly different in different seasons with three peaks in spring (morning and evening rush hours and around noon), single peak in summer (around noon) and bimodal pattern in fall and winter (morning and evening rush hours), indicating the effects of new particle formation and human activities. Diurnal variations of particle number concentrations in other modes were bimodal (morning and evening rush hours), but the time of peaks was different, e.g. peaks appeared at 08:00 am and 11:00 am in summer and winter, respectively, which may be related to the differences in the evolution of planetary boundary layer and the mountain-valley winds in urban Lanzhou. Particle number size distributions were generally unimodal all year around, but the mode diameters in wintertime were significantly larger than those in summertime. The number concentrations of particles in Aitken and accumulation modes in winter half year were much higher than those in summer half year. The high fractions of particles large than 50 nm in wintertime were mainly related to coal burning and poor diffusion conditions, while the high particle number concentration in nucleation mode in summertime was related to the frequent occurrence of new particle formation and growth events in spring and summer. 2) New particle formation (NPF) events were observed on 40% of the measurement days, which occurred most frequently in spring and summer with the maximum in May and August and the minimum in January. Most of the NPF events were observed on sunny, dry and windy days. The concentrations of SO2 and O3 were much higher on NPF days than other days, while the concentrations of NO2 and CO were comparable. Low concentrations of pre-existing particles were essential for the occurrence of NPF events in urban Lanzhou. The range of formation rate spanned from 2.52 to 22.41 cm-3 s-1 and the growth rate varied from 3.75 to 6.08 nm h-1, consistent with other observations found in the literatures. 3) Air temperature, RH, wind speed and precipitation have significantly different effect on the variations of the numbers of particles in different sizes in different seasons. Particles number concentrations mainly depended on wind speed in spring. The particle number concentrations in Aitken and accumulation modes were more sensitive to air temperature in fall, while they depended not only on air temperature but also RH and wind speed in summer. The effects of meteorological conditions on mode diameters were the most obvious in summer. The mode diameters of particle number size distributions significantly decreased or increased as temperature or relative humidity increased in summer, respectively. Furthermore, the mode diameters decreased from ~70 nm to ~20 nm as wind speed increased in spring and summer. The snow scavenged particles more efficiently in the size ranges of 20-1000 nm and 2000-10000 nm than rain. For particles in 1000-2000 nm, rain was more efficient for scavenging. The scavenging coefficients of snow varied more obviously with particle sizes than that of rain, and snow can scavenge particles efficiently, especially the coarse particles with aerodynamic diameters larger than 4 μm. The snow scavenging coefficient varied between 3.11×10-7 s-1 and 1.18×10-3 s-1 in size range 10-10000 nm, while for rain, it was between 3.18×10-6 s-1 and 7.46×10-4 s-1. Non-thunderstorm rain could efficiently scavenge particles smaller than 500 nm, while thunderstorm rain could scavenge particles in 500-1000 nm more effectively. The scavenging coefficient of thunderstorm rain for 10-10000 nm particles were between 8.25×10-7 s-1 and 1.23×10-3 s-1, while that for non-thunderstorm rain varied between 7.48×10-6 s-1 and 7.46×10-4 s-1. 4) For dust from different origins, their effect on the particle size distributions and their modal parameters, such as volume median diameter (VMD), and the evolutions of particle size distributions before, during and after dust events at downstream cities are significantly different. As far as particle volume size distributions were concerned, the VMDs of the two modes for DS1 (dust mainly originated from the desert regions in central and western Inner Mongolia) and DS2 (dust mainly came from Taklimakan desert and its outer edges) in urban Lanzhou were 3.0±0.2 μm, 5.0±0.1 μm (DS1) and 2.7±0.04 μm, 3.8±0.03 μm (DS2), respectively, indicating significant difference in the size of dust particles from different source regions. The possibility of using the atmospheric particle size distributions during dust event and their modal parameters at downstream cities to deduce the dust source regions were investigated by combining information from satellite observations from MODIS and CLIPSO and backward trajectory calculations. 5) The interactions between atmospheric particles and temperature inversions and the role of mountain heating on the daytime elevated temperature inversions were investigated. The analysis of the frequency of three types of temperature profiles (those having near surface inversion, elevated inversion and no inversion, respectively) and their corresponding mean particle number size distributions revealed that the particle number size distributions were similar under different temperature profiles, but particle number concentration in different size bins were significantly different. The number concentrations were the highest and the lowest for conditions with near surface inversion and no inversion, respectively, especially for particles in the size range of 30-300 nm. Particle number concentrations in Aitken and accumulation modes were high when temperature inversion existed. The daytime elevated inversions were affected mainly by mountain heating and the direct radiative effects of accumulation mode particles, while the near surface inversions were related to the positive feedbacks between particles in Aitken and accumulation modes and the near surface temperature inversion. |
| 中文关键词 | 山谷城市 ; 大气颗粒物 ; 谱特征 ; 气象条件 ; 新粒子生成 ; 沙尘 ; 逆温 ; 聚类分析 ; 主成分分析 |
| 英文关键词 | Valley city particles size distributions meteorological conditions new particle formation dust temperature inversion cluster analysis principal component analysis |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 大气物理学与大气环境 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287538 |
| 推荐引用方式 GB/T 7714 | 赵素平. 兰州城市气溶胶谱特征及其与大气逆温的相互作用研究[D]. 中国科学院大学,2015. |
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