泰山气溶胶化学及云微物理过程研究

发布时间：2019-05-27 01:30

【摘要】：云雾是包括气相、液相和固相的非均相复杂体系,研究云雾过程及云雾样品中的污染物浓度,有利于揭示大气中污染组分的生成、迁移、转化。泰山是华北平原的最高点,其污染程度能代表华北地区的本底值。本论文的主要研究对象是2014年7月至10月间,和2015年6月至8月间,两年内共观测到的46次云雾事件和采集到的78个云雾水样品。本文总结了云雾水的化学组分、颗粒物与云雾化学组分之间的关系,以及云雾事件的微物理特征。泰山云雾样品使用美国科罗拉多州立大学(Colorado State University)研制的 CASCC2(Caltech Active Strand Cloud water Collector Version 2)型云雾采样器进行采集,原位测量pH和电导后,实验室分析其中的水溶性离子、多环芳烃和重金属。云雾事件使用雾滴谱仪(Fog Monitor,Model FM-100,Droplet Measurement Technologies)进行观测,得到的微物理特征(包括云雾液滴的数浓度、含水率、有效粒径和中值粒径)结合云雾样品的化学组分,和云雾事件发生时的气象数据、PM2.5浓度,探究云雾液滴的形成和发展特征以及大气中气溶胶相-液相之间化学组分的转化。通过对云雾样品的研究发现,云雾水2014年和2015年的pH体积平均值分别为5.87和5.62,远高于2007-2008年同观测点观测到的云雾水pH值3.86[1]。泰山地区云雾水的电导率高于世界其他高山地区云雾水的电导率,这表明泰山云雾水中的污染物浓度较高。云雾水中的主要离子为NH4+、SO42-、Ca2+和NO3-。其中,NH4+和Ca2+是中和云雾水酸性最为重要的阳离子,云雾事件发生期间,这两种阳离子浓度的升高,导致了 2014年和2015云雾水pH值的升高。(NH4)2SO4和NH4N03是大气中的主要吸湿性成分,云雾事件的发生往往伴随着NH4+、SO42-、NO3-浓度的升高。PM2.5可能是云雾水中可溶性离子和致酸组分的主要来源,PM2.5含有的可溶性离子通过溶解、扩散、稀释和液相反应等过程进入云雾液滴中,其浓度越高,云雾水中测量到的可溶性离子总浓度越高,pH值越小。后向气流轨迹分析显示,气团来源对2014年和2015年云雾水中污染物浓度有一定的影响,导致两年的化学组分存在一定的差异。通过研究云雾的微物理参数发现,不同云雾事件之间的云雾液滴含水率和数浓度相差较大,但观测到的云雾液滴直径均小于26.0 μm,大部分分布在6.0-9.0μm之间,云雾液滴的数浓度峰值在7.0μm附近。观测发现,大气相对湿度的升高和PM2.5浓度的降低,会促进云雾液滴数浓度的降低,并且有利于大粒径云雾液滴的形成,此时云雾含水率增加。因此,在估计云雾水中污染物的浓度时,应同时考虑液滴对污染物的稀释作用。最后,我们总结了云雾液滴的形成机理图。结果显示,PM2.5浓度越高,大气中的云凝结核浓度增加,对大气水分的竞争增加,更易形成小粒径云雾液滴,且云雾水中可溶性离子浓度升高,反之亦然。
[Abstract]:Cloud fog is a heterogeneous complex system including gas phase, liquid phase and solid phase. The study of cloud and fog process and the concentration of pollutants in cloud samples is helpful to reveal the formation, migration and transformation of pollution components in the atmosphere. Mount Tai is the highest point in North China Plain, and its pollution degree can represent the background value of North China. The main research objects of this paper are 46 cloud and fog events and 78 cloud water samples collected from July to October 2014 and June to August 2015. In this paper, the chemical components of cloud and fog water, the relationship between particles and cloud chemical components, and the microphysical characteristics of cloud and fog events are summarized. Mount Tai cloud samples were collected by CASCC2 (Caltech Active Strand Cloud water Collector Version 2) cloud sampler developed by Colorado State University (Colorado State University). After in situ measurement of pH and conductivity, the water soluble ions were analyzed in the laboratory. Polycyclic aromatic hydrocarbons (PAHs) and heavy metals. The cloud event was observed by fog drop spectrometer (Fog Monitor,Model FM-100,Droplet Measurement Technologies). The microphysical characteristics (including the number concentration of cloud droplets, water content, effective particle size and median particle size) were combined with the chemical components of cloud and fog samples. The formation and development characteristics of cloud droplets and the transformation of chemical components between aerosol phase and liquid phase in the atmosphere were investigated with meteorological data and PM2.5 concentration at the time of cloud and fog events. Through the study of cloud and fog samples, it is found that the average pH volume of cloud and fog water in 2014 and 2015 is 5.87 and 5.62, respectively, which is much higher than the pH value of cloud and fog water observed at the same observation point from 2007 to 2008. The conductivity of cloud water in Mount Tai is higher than that in other alpine areas of the world, which indicates that the concentration of pollutants in cloud and fog water in Mount Tai is higher. The main ions in cloud water are NH4, SO42-,Ca2 and NO3-.. Among them, NH4 and Ca2 are the most important cations in neutralizing cloud water acidity. During the cloud fog event, the concentrations of these two cations increased. Led to the increase of pH value of cloud and fog water in 2014 and 2015. (NH4) 2SO4 and NH4N03 are the main hygroscopic components in the atmosphere, and the occurrence of cloud and fog events is often accompanied by NH4, SO42-,. The increase of NO3- concentration. PM2.5 may be the main source of soluble ions and acidic components in cloud water. The soluble ions contained in PM2.5 enter into cloud droplets through dissolution, diffusion, dilution and liquid phase reaction, and the higher the concentration of PM2.5 is, the higher the concentration of PM2.5 is. The higher the total concentration of soluble ions measured in cloud water, the smaller the pH value. The analysis of backward airflow trajectory shows that the source of air mass has a certain effect on the concentration of pollutants in cloud and fog water in 2014 and 2015, resulting in some differences in chemical components between the two years. By studying the microphysical parameters of cloud and fog, it is found that the moisture content and numerical concentration of cloud droplets vary greatly among different cloud and fog events, but the diameter of cloud droplets observed is less than 26.0 渭 m, most of which are distributed between 6.0 渭 m and 9.0 渭 m. The peak concentration of cloud droplets is about 7.0 渭 m. It is found that the increase of atmospheric relative humidity and the decrease of PM2.5 concentration will promote the decrease of cloud droplet concentration, and will be beneficial to the formation of large particle size cloud droplets, and the water content of cloud fog will increase at this time. Therefore, when estimating the concentration of pollutants in cloud and fog water, the dilution effect of droplets on pollutants should be considered at the same time. Finally, we summarize the formation mechanism diagram of cloud droplets. The results show that the higher the concentration of PM2.5 is, the higher the concentration of cloud condensation nucleus in the atmosphere is, and the competition for atmospheric moisture is increased, and it is easier to form small particle size cloud droplets, and the concentration of soluble ions in cloud water increases, and vice versa.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513

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