硝酸—氨气体系的大气团簇均相成核的理论研究

发布时间：2018-01-14 22:20

本文关键词：硝酸—氨气体系的大气团簇均相成核的理论研究　出处：《中国科学技术大学》2017年硕士论文　论文类型：学位论文

【摘要】：长久以来,全球气候发生了明显的变化,局部或者全局区域的雾霾事件也越来越严重,这与大气气溶胶有着密不可分的关联。气溶胶颗粒物使得人们人们视野范围受限,交通事故频繁发生,且对人体健康有着不可忽视的重大影响,造成心肺功能不可逆的损害。另一方面从历史趋势来看温室效应越来越严重,但是随着雾霾天气状况的频频发生,温室效应的趋势却越来越平缓,这之中的原因与气溶胶的参与有很大关联,气溶胶由于其自身的理化性质可以直接影响太阳光线的净通量,即直接影响辐射强迫,还可以使得云层的厚度产生变化和云的存在时间长短来间接地改变地球-热量系统的出入均衡,因此负辐射强迫作用可以对温室加热效应有抵消作用。气溶胶的作用可褒可贬。而了解气溶胶的第一步是研究气-相转化的成核与生长机制。不同类型的气溶胶对气候的作用效果不一样,硫酸盐型气溶胶是作用效果最明显的,具有负的辐射强迫的气溶胶,但是硫排放逐渐减少,硝酸盐气溶胶的作用逐渐增长,在大气气溶胶组分中地位不断上升,它也具有负的辐射强迫,可以抵制温室效应带来的极端气候的影响。随着氨气的大量排放,硝酸盐气溶胶大量形成,这成为雾霾状况更加严重的诱因之一,从而为居民的正常生活带来了一系列的危害。本文中通过随机算法和人工蜂群算法来搜索构型,然后通过量子化学程序计算结合能,初步模拟了硝酸和氨气二元化合物由气相单体逐渐生长为超细气溶胶团簇的过程。计算了各个团簇的生长所需能量,以及硝酸和氨气单体生长每一步的自由能垒,为了解硝酸-氨气体系全局稳定性和成核生长机理提供了基础。具体成果如下:1.在计算方面,本论文采用随机算法结合高斯量化程序搜索团簇初始构型,随机算法在搜索分子团簇构型方面有很成熟的应用。论文中选用B3LYP杂化密度泛函以及D3色散修正作用,B3LYP在描述色散作用比较薄弱,所以选用DFT-D3能够很好的引入色散修正,对长程相互作用有很好的描述。基组重叠误差也是影响结果的一个因素之一,本论文中使用的是6-311++G(d,p)基组,考虑到大基组可以避免高估电子相关作用,能够比较好地描述分子轨道。2.在团簇生长热力学性质方面计算,对硝酸和氨气在不同化学计量比下形成的团簇的热力学性质的计算结果显示,质子转移以及氢键网络在团簇稳定成核降低自由能的过程中尤其重要,硝酸和氨气加入到前体团簇中成核过程的自由能垒与硫酸-氨气体系不同,在大气气溶胶生长过程中没有发挥比较明显的作用。由生长自由能反映的蒸发速率可以凸显不同的分子单体在整体团簇中的稳定性,一般来说团簇越大越稳定,硝酸和氨气分子数化学计量比相等可以有效降低团簇稳定性,除了起过渡作用的团簇结构会发生例外。当团簇分子总数相同,即m-n和n-m比较时,酸的蒸发速率较氨气低,所以团簇的成核生长取决于酸在体系中的衰减速率。
[Abstract]:For a long time, changes in global climate, local or global regional haze events are becoming more and more serious, which has a close relation with atmospheric aerosol particles. People limited the scope of vision, frequent occurrence of traffic accidents, and has a great influence to the human health, cause heart and lung the function of irreversible damage. On the other hand from the historical trend of greenhouse effect becomes more and more serious, but with the haze weather occurred frequently, the greenhouse effect of the trend is more and more gentle, is of great relevance to the cause of the aerosol and aerosol in the physical and chemical properties of its own can directly affect the net flux of the sun the light, which directly affect the radiative forcing, but also can make the cloud thickness and cloud is the length of time to indirectly change earth heat system Out of balance, so the negative radiative forcing effect can offset the effects of greenhouse heating effect. The aerosol effects of them. The first step is aerosol nucleation and growth mechanism of gas phase transformation. The effect of different types of aerosols on the climate is not the same, is the most obvious effect of sulfate aerosol the effect of aerosol radiative forcing is negative, but sulfur emissions decreased, nitrate aerosol effects gradually increasing in atmospheric aerosol component status is rising, it also has a negative radiative forcing effect can be brought against extreme climatic greenhouse. With ammonia emissions, a large number of nitrate aerosol this is one of the causes of haze formation, situation is more serious, which has brought a series of harm to the normal life of the residents. The random algorithm and artificial bee colony algorithm by this paper To search the configuration, and then through the quantum chemistry program to calculate the binding energy, the simulated process of nitrate and ammonia two compounds by gas phase monomer gradually grew into ultrafine aerosol clusters. The energy required for each cluster growth were calculated, and the nitrate and ammonia single growing every step of the free energy barrier for. To understand the global stability of nitrate and ammonia system - nucleus growth mechanism provides the basis. The main results are as follows: 1. in terms of computation, this paper adopts random algorithm with Gauss quantization procedure search cluster initial configuration, random algorithm is used to search in mature cluster configuration. Using B3LYP hybrid density functional and D3 dispersion correction the role of B3LYP in the thesis, describe the dispersion effect is relatively weak, so we choose DFT-D3 to introduce good dispersion correction, the long-range interactions are well described. Basis set superposition error is One of the factors that influence the results, used in this paper is the 6-311++G (D, P) basis set, taking into account the large groups can avoid overestimating the electron correlation effect, can better describe the thermodynamic properties of.2. molecular orbital growth in cluster calculation, calculation of the thermodynamic properties of ammonia and nitrate in different chemical cluster under the formation of the stoichiometric results showed that proton transfer and hydrogen bond network in the cluster nucleation process is especially important decrease in the free energy, nitrate and ammonia added to the nucleation process of precursor clusters in the free energy barrier and ammonia sulfuric acid system, did not play obvious role in atmospheric aerosol growth in the process of stability. Monomer in the overall cluster in different molecules by highlighting the evaporation rate of growth of free energy can reflect, in general clusters is more stable, nitrate and ammonia molecular number of stoichiometric phase Such an effect can effectively reduce cluster stability. Excepting the transition cluster structure, when the total number of clusters is the same, that is, when M-N and N-M are compared, the evaporation rate of acid is lower than that of ammonia. Therefore, the nucleation growth of clusters depends on the decay rate of acids in the system.

【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513;O648.16

【参考文献】