Condensation particle counting below 2 nm seed particle diameter and the transition from heterogeneous to homogeneous nucleation     

Paul M. Winkler  Aron Vrtala  Paul E. Wagner 《Atmospheric Research》2008,90(2-4):125-ICNAA07

Particle detection by condensation particle counters (CPCs) is ultimately limited by the onset of homogeneous nucleation. At vapour supersaturations around the homogeneous nucleation limit the diameter of critical clusters is typically about 2 nm. It is widely assumed that only particles larger than critical clusters can be activated by vapour condensation and the general detection limit of CPCs is therefore currently accepted to be around 2 nm particle diameter. Using an expansion type CPC with n-propanol as working fluid we investigated the transition from heterogeneous to homogeneous nucleation, clearly showing that particles are activated much before the onset of homogeneous nucleation, even at particle diameters as small as 1.4 nm. For particle diameters below 2 nm we have usually found condensation particle counting to be influenced by the simultaneous presence of ions as generated in a bipolar diffusion charger. In this paper we illustrate how the presence of ions influences particle number concentration measurement and how ions can be removed in order to obtain accurate seed particle number concentrations for particle diameters down to 1 nm.  相似文献   

昆明全天空流星雷达观测中高层大气温度   总被引：3，自引：1，他引：2       下载免费PDF全文

易稳  陈金松  马春波  李娜  赵振维 《地球物理学报》2014,57(8):2423-2432

利用昆明电波观测站（25.6°N，103.8°E）两台不同工作频率的全天空流星雷达在2011年特殊联合观测试验期间的数据，基于Hocking的方法利用不同的温度梯度，在确定了昆明地区中层顶位于流星峰值高度之上的情况下，反演了昆明地区上空88 km和85 km高度的大气温度，并与Aura卫星观测的温度进行比较.对比研究发现，两台流星雷达可以分别正确获得88 km和85 km高度的大气温度，但其中由全球温度梯度模式反演得到的大气温度与卫星观测温度相关性不是很好，而利用卫星观测的温度梯度，两台雷达反演出的大气温度与卫星观测温度存在很好的相关性.结果表明了准确的温度梯度在流星雷达观测大气温度过程中是至关重要的.  相似文献   

Toroidal magnetic field structure of the solar convective envelope inferred from the initial observations of the sunspots     

K.M. Hiremath  M.R. Lovely 《New Astronomy》2012,17(4):392-398

For different life spans, we measure the line of sight component of the magnetic field structure of the bipolar sunspots from the SOHO/MDI magnetograms during their initial appearance on the surface and toroidal component of the magnetic field structure is separated. Irrespective of their sizes, strength of the measured line of sight component of the magnetic field structure varies from ∼450 G for the life span of 2 days to ∼300 G for the life span of 12 days. Where as strength of the estimated surface toroidal component of the bipolar spots varies from ∼10 G for the life span of 2 days to ∼700 G for the life span of 12 days. We use rederived Parker’s (1955a) flux tube model in spherical coordinates and Hiremath’s (2002) life span anchoring depth information to infer the strength of line of sight and toroidal components of the magnetic field structures at different anchoring depths of the bipolar spots in the convective envelope and the important findings are: (i) both the line of sight and toroidal components of the magnetic field structures at the sites of sunspots’ different anchoring depths in the convective envelope have a similar radial variation and the strength (∼10⁴ G near base of the convective envelope to ∼100 G near the surface) and, (ii) rate of emergence of toroidal magnetic field structure near base of the convective envelope is estimated to be ∼100 times the rate of emergence of toroidal magnetic field structure near the surface.  相似文献   

兴蒙造山带中二叠世哲斯期腕足动物古生物地理归属   总被引：2，自引：0，他引：2  

张松梅  王成文 《地球科学进展》2004,(Z1)

两极分布的凉水型分子是古地理一级区划的重要标志之一。根据兴蒙遣山带中二叠世哲斯期的10个腕足动物属(族)的地理分布的特征分析,Yakovlevia等腕足动物的地理分布具有两极分布的特点。是典型的凉水型的腕足动物,并具有亲北极生物的特征,其古生物地理区划应该属于北方大区。  相似文献