【作者】 岳岩裕；

【导师】 牛生杰；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2013， 博士

【摘要】 本文利用2010年3-4月和2011年2-3月中国广东省湛江市东海岛两期海雾外场观测试验中获得的常规气象要素、边界层结构、能见度、雾水样本以及雾滴、雨滴和气溶胶粒子谱等资料,综合分析了海雾发生期间的天气形势、气象要素和海温的变化特征；对海雾发生期间雾滴谱、雨滴谱和气溶胶谱的演变特征及其之间的联系进行了深入研究,探讨了影响海雾形成和发展的主要机制；研究了海雾雾水离子浓度的变化规律,并进行了两期观测结果的对比研究；最后,基于雾水化学组分和宏微观要素的变化特征,探讨了不同因子对海雾雾水化学特征的影响。得到的主要结论如下：(1)雷州半岛年平均雾日数为20～30d。气温为16-22℃时,雾日较多。当东海岛位于低压前部或受到冷锋影响时,海雾出现的概率最高,且一般都有逆虚温存在。海雾发生期间近地层平均风速为1-5m s-1,以偏东风为主,且随高度顺转。海温基本处于18-21℃,高层风向偏南、气温高于海温对南海海雾的形成起到了重要作用。(2)针对雾日三种粒子(雾滴、气溶胶和雨滴)的变化进行分析发现：海雾雾滴数浓度少于城市地区的雾,且液态水含量(LWC)一般较低,这与海陆交界处湍流沉降加速导致大雾滴较少,且部分超过探测范围的雾滴观测不到有关。通过雾微物理特征量间的相关性分析发现,核化凝结增长是雾滴形成的关键,而雾滴形成后的发展受多种因子影响,碰并、湍流和平流因子的影响与其他类型雾相比较强。雾滴谱符合Gamma分布,且随着碰并作用增强,滴谱增宽。气溶胶谱呈单峰分布,其数浓度与其他地区相比低1个数量级,雾日的气溶胶数浓度与非雾日相比显著下降,雾滴和气溶胶数浓度的比值(Nf/Na)随着LWC增大而增加。雨雾过程中大气层结稳定,近地面气温较低,雾滴谱偏窄。(3)2010年雾水的pH和电导率(EC)平均值分别为5.20和1884μScm-1;2011年的pH和EC平均值分别为3.34和505μS cm-1。pH值和EC之间呈负相关关系。2011年雾水酸性变强的原因主要考虑酸性物质比重增加。海洋源离子Cl-和Na+的离子浓度很高；S042-和NO3-具有同源性,人为污染的贡献明显。通常情况下随着海雾发展,雾水离子浓度经历“U”型变化,这与大气中离子负荷量和LWC变化等因素有关。2010和2011年总离子浓度(TIC)的平均值分别为38260μeq L-1和5600μeq L-1,而实际大气中离子负荷量相差不大,主要由于2011年观测地点海拔高度的升高会降低湍流因子的影响,减少粒径较大雾滴的沉降,从而促使LWC增加,在大气中污染物质浓度变化不大的情况下,离子浓度下降。(4)雾水成分在一定程度上依赖于气溶胶粒子的种类和大小,受到北方特大沙尘暴影响,东海岛地区直径大于1μm的气溶胶粒子数浓度显著增加,导致雾水中Ca2+和Mg2+的离子浓度明显升高。雨雾过程中TIC的起伏变化不明显,TIC的标准偏差最小。受到冷锋和低压系统影响时大气中离子的负荷量减少。当气团路径较短,受局地污染源影响时,离子负荷量最高,而当气团完全来自于海洋时,其值最低。采集效率随着风速的增加递减,最大TIC对应的风速、风向和气温区间分别为3.5-4m s-1,78.75-90°和21-22℃。综合考虑各个微物理特征量与TIC之间的关系提出一个新参量1/(LWC×r),其反映了清除效率(1/r)和稀释作用(LWC),相关系数为0.74。更多还原

【Abstract】 During two sea-fog field observation programs on Donghai Island in Guangdong province of China from March to April2010and from February to March2011, meteorological elements, structures of the atmospheric boundary layer, visibility, fog water, and spectrum of rain droplets, fog droplets and aerosols were obtained. The variations of synoptic systems, meteorological elements and sea surface temperature (SST) were analyzed. We studied the evolution and relationship of rain droplets, fog droplets and aerosols during the sea fog cases, as well as the dominant mechanisms of fog formation and development. The analysis on chemical compositions of sea fog and the comparative study were carried out to display the properties of fog-water. Finally, we discussed the effect of different factors on sea fog water ion concentrations based on the analysis of sea fog water chemical composions and different macro-and microphysical elements. The main conclusions are as follows:(1)The average fog days in Leizhou Penisular were20-30d. When the temperature was16～22℃, the fog days were relatively high. Most sea fog cases were affected by depression and cold front, with virtual temperature inversion. The average wind speed was1～5m s-1; the dominate wind direction was from east and clockwise rotation with height. The SST was about18～21℃, the wind from south and air temperature higher than SST was propitious to fog as well.(2) Based on the analysis of microphysical characteristics of fog droplets, aerosols and rain droplets, we found that:The number concentration of sea fog was lower than that of continent fog with relatively low liquid water content (LWC), due to the low number concentrations of large fog droplets caused by turbulence deposition and some droplets exceeding the measuring range. Activation and condensation growth played an important role on fog droplets formation and growth. Compared with continent fog and mountain fog, the influences of collision-coalescence, turbulence and advection factors were more significant in sea fog. The spectra of fog droplets could be expressed by formula of Gamma and spectra width broadened by the strength of collision-coalescence. The distribution of aerosol was unimodal. The number concentration of aerosol was one order of magnitude lower than that in other regions, and the aerosol number concentration decreased significantly during the fog cases. The ratio of number concentration between fog droplets and aerosol (Nf/Na) increased with the growth of LWC. The precipitation fog occurred with stable atmospheric stratification, and the temperature near the surface was low. The width of fog droplets spectrum was narrow.(3)The average pH and electrical conductivity (EC) value in2010was5.20and1884μS cm-1; while the average values of pH and EC in2011were3.34and505μS cm-1, respectively, and the pH value had a negative correlation with EC. The fog water became more acidity in2011might owing to the proportion of acidity and alkalinity matter. Cl-and Na+mainly originated from oceanic aerosols; NO3-and SO42-could be influenced by the same source, such as anthropogenic pollutions. The variation pattern of ion concentration was in form of "U", related to the ion loading and LWC. The average total ion concentration in2010and2011were38260μeq L-1and5600μeq L-1, respectively, but the ion loadings were almost in the same magnitude. When the pollutant substances emission changed little, the decline of TIC was owing to the growth of LWC caused by the decline of turbulence with the rise of altitude.(4)The chemical composition of fog water was depended upon the species and size of aerosols. Affected by one large dust storm originated from the north of China, the number concentration of large aerosol particles (with a diameter larger than1μm) increased, indicating that the concentrations of Ca2+and Mg2+in fog water increased. During the precipitation fog, the extent of variation was slight, with the lowest standard deviation. Cold front and depression promoted the decline of ion loading. The air mass from a short distance away was mainly affected by pollutants from coastal areas and had the highest ion loading, while the airflow from the sea had the lowest ion concentration and ion loading. The collection efficiency decreased with the increase of wind speed. The ranges of wind speed, wind direction and temperature corresponding to the maximum total ion concentration (TIC) were3.5～4m s-1,78.75～90°and21～22℃, respectively. In view of low correlation coefficients between microphysical characteristic quantities and TIC, a new parameter of Lr=1/(LWC×r) was proposed as a predictive parameter for TIC, where1/r and LWC represented scavenging efficiency and dilution effect. The correlation coefficient between Lr and TIC was0.74.更多还原