大气气溶胶VH-TDMA装置建立及吸湿和挥发特性研究

发布时间：2019-05-17 22:06

【摘要】：环境污染是目前制约我国经济社会可持续发展的重要问题之一,大气气溶胶是大气复合污染的重要成分,其物理化学性质在大气环境及辐射效应等方面有着至关重要的作用,是环境和气候变化领域的研究热点。气溶胶的吸湿特性显著改变颗粒物的粒径、光学特性、云凝结核活性以及化学反应活性,进而对大气能见度、辐射强迫、酸沉降以及人体健康产生直接和间接的重要影响。黑碳气溶胶是全球气溶胶最大的吸收体,其光吸收特性与大气中的混合状态密切相关,是人们关注的焦点问题。由于实际大气气溶胶的复杂性,它的吸湿性质和黑碳气溶胶的混合态是气溶胶直接辐射强迫评估不确定性最大的两个关键因素。本文设计建立了一套挥发性吸湿性-串联差分电迁移率分析仪装置(Volatility Hygroscopic-Tandem Differential Mobility Analyzer,VH-TDMA)。挥发特性测量单元由四根加热管并列组成,加热温度分别为25℃,150℃,250℃,和350℃,可实现不同加热温度之间的快速切换,与传统的VTDMA相比,可以获得更高的时间分辨;吸湿特性测量单元利用全氟磺酸管设计的加湿系统可以将气溶胶粒子的相对湿度稳定控制在10%至90%相对湿度范围内,相对湿度的精度为1%。利用实验室气溶胶发生系统产生的氯化钠和硫酸铵气溶胶,对该装置的粒子损耗、挥发及吸湿特性测量的准确性进行了评估,通过与其他研究小组的结果对比,验证了系统的可靠性和准确性。使用H-TDMA研究了在10～90%RH条件下与灰霾相关的两种水溶性有机物(草酸和丁二酸)与典型无机盐(硫酸铵和硝酸铵)内混合粒子的吸湿特性,并结合Zdanovskii-Stokes-Robinson(ZSR)模型和扩展-无机气溶胶热力学模型(Extended-AIM Aerosol Thermodynamics Model)理论预测内混合粒子的吸湿特性,分析了草酸和丁二酸在加湿过程中的相态变化对于硫酸铵和硝酸铵吸湿特性的影响。2016年夏季,运用建立的V-TDMA装置在安徽省寿县国家气候观象台进行了系列外场观测实验。一方面,研究了不同粒径(50nm-350nm)黑碳气溶胶的混合态,将加热挥发之后的粒谱分为高挥发性(high volatile,HV)、中等挥发性(medium volatile,MV)和低挥发性(low volatile,LV),HV、MV 和 LV 的数浓度平均分数与粒径呈显著的相关性。定义中等挥发性颗粒数浓度分数(Fin)为衡量气溶胶混合态的参数。Fin的结果表明当地外混合BC主要集中在小粒径范围,并且大粒径的MV和LV高值可能是由于颗粒物在到达乡村背景站点过程中充分老化。充分集中的相对频率分布和并不显著的日变化表明传输的气团和本地排放源具有相似的老化状态。与相似的研究对比发现,不同粒径颗粒物的Fin值存在明显差别,直接排放的黑碳气溶胶的Fin值较低,而随着老化程度越高,对应的Fin值也越高,Fin的均值是直接排放和老化过程竞争的结果。对于不同粒径的Fin的PSCF值在空间分布中都呈现不同,表明不同尺寸内混合含碳气溶胶的潜在源贡献来源是有区别的。研究结果还表明传输对于寿县站点地区黑碳气溶胶的混合态起着主要作用,并且显示出与粒径的相关性。另一方面,开展了 90%高相对湿度条件下50～250nm环境气溶胶的吸湿特性研究,该地区气溶胶吸湿增长之后的谱分布多呈现单峰或双峰分布,强弱吸湿增长可以明显区分,弱吸湿组分的平均吸湿增长因子为1.07,强吸湿组分的吸湿增长因子在1.37～1.56之间并与粒径呈正相关关系。当地多分散气溶胶吸湿增长之后的平均谱分布较未吸湿的平均谱分布出现峰值向右偏移稍微增大和双峰分布的现象,表明了当地大气中不同粒径颗粒物的吸湿能力以及强弱吸湿组分比例不一样;不同时间段(白天和夜晚)多分散气溶胶加湿与否的平均谱分布差异反映了细粒子颗粒物主要来源于本地排放,强吸湿性大粒径颗粒物主要来自于远距离传输影响。
[Abstract]:Environmental pollution is one of the most important problems in the sustainable development of China's economy and society, and the atmospheric aerosol is an important component of the atmospheric composite pollution, and its physical and chemical properties play an important role in the atmospheric environment and the radiation effect. Research hot spots in the area of environmental and climate change. The moisture-absorbing properties of the aerosol can significantly change the particle size, optical characteristic, cloud-condensed nodule activity and chemical reaction activity, and further have a direct and indirect effect on the atmospheric visibility, radiative forcing, acid deposition and human health. Black carbon aerosol is the largest absorber of global aerosol, and its light absorption characteristic is closely related to the mixed state in the atmosphere, which is the focus of people's attention. Because of the complexity of the actual atmospheric aerosol, the mixed state of its hygroscopic nature and the black carbon aerosol is the two key factors of the greatest uncertainty of the direct radiative forcing assessment of the aerosol. A set of volatile moisture-absorbing-tandem differential mobility analyzer (VH-TDMA) is designed. the volatilization characteristic measuring unit is composed of four heating pipes, the heating temperature is 25 DEG C,150 DEG C,250 DEG C and 350 DEG C, the fast switching between different heating temperatures can be realized, and a higher time resolution can be obtained compared with the traditional VTDMA; The moisture absorption characteristic measuring unit can stably control the relative humidity of the aerosol particles in the range of 10% to 90% relative humidity by using the humidifying system designed by the perfluorosulfonic acid pipe, and the accuracy of the relative humidity is 1%. The accuracy of the measurement of particle loss, volatilization and moisture absorption characteristics of the device is evaluated by using the sodium chloride and the sulfur dioxide aerosol generated by the laboratory aerosol generating system, and the reliability and the accuracy of the system are verified through comparison with the results of other research groups. the moisture-absorbing properties of the mixed particles of the two water-soluble organic matter (oxalic acid and succinic acid) associated with the haze and the typical inorganic salts (sulfuric acid and nitrate) under the condition of 10-90% rh were studied using h-tdma, In this paper, the effects of the phase change of oxalic acid and succinic acid in the humidification process on the moisture absorption characteristics of the sulfuric acid and the nitrate are analyzed with the combination of the Zdanovskii-Stokes-Robinson (ZSR) model and the extended-AIM Aerosol Thermodenics Model, and the effect of the phase change of the oxalic acid and the succinic acid in the humidification process on the moisture absorption characteristics of the sulfuric acid and the ferric nitrate is analyzed. In the summer of 2016, A series of field observation experiments were carried out in the national climate observation station of Shouxian County, Anhui Province using the established V-TDMA device. On the one hand, the mixed state of black carbon aerosol with different particle size (50 nm-350 nm) is studied, and the grain spectrum after heating and volatilization is divided into high volatile (HV), medium volatile (MV) and low volatility (LV), HV, The mean fraction of the number of MV and LV was significantly correlated with the particle size. A medium-volatile particle number concentration fraction (Fin) is defined as a parameter to measure the aerosol mixing state. The results of the Fin show that the local external mixed BC is mainly concentrated in the small particle size range, and the MV and LV high values of the large particle size may be due to the full aging of the particulate matter in the process of reaching the rural background site. The relative frequency distribution and the non-significant diurnal variation of the sufficiently concentrated show that the transmitted air mass and the local emission source have similar aging states. In comparison with similar studies, there was a significant difference in the Fin values of different particle size particles, and the Fin value of the direct emission of the black carbon aerosol is low, and the higher the value of the corresponding Fin value as the degree of aging is, the average value of the Fin is the result of the direct emission and the competition of the aging process. The PSCF values for Fins of different particle sizes are different in the spatial distribution, indicating that the potential source contribution sources of mixed carbon-containing aerosols in different sizes are different. The results of the study also show that the transmission plays a major role in the mixed state of the black carbon aerosol in Shouxian station, and shows the correlation with the particle size. On the other hand, the moisture absorption characteristics of 50 ~ 250nm environmental aerosol at 90% relative humidity were studied. The spectral distribution after the growth of the aerosol in this area showed a single peak or a double peak distribution, and the strong and weak hygroscopic growth could be clearly distinguished. The average moisture absorption and growth factor of the weak moisture absorbent component was 1.07. The hygroscopic growth factor of the strong moisture absorbent component is between 1.37 and 1.56 and is positively related to the particle size. The average spectral distribution of the local multi-dispersed aerosol is slightly increased and the double-peak distribution of the non-hygroscopic average spectral distribution, indicating that the moisture-absorbing ability and the proportion of the strong and weak moisture-absorbing components of the different particle-size particles in the local atmosphere are different; The difference of the average spectral distribution of the multi-dispersed aerosol in different time periods (day and night) reflects that the fine-particle particles mainly come from the local emission, and the large-particle-size particles with strong moisture absorption mainly come from the influence of long-range transmission.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X513

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