Sakurai Hiromu, Park Kihong, McMurry Peter H, Zarling Darrick D, Kittelson David B, Ziemann Paul J
Particle Technology Laboratory, Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Environ Sci Technol. 2003 Dec 15;37(24):5487-95. doi: 10.1021/es034362t.
Mixing characteristics of particles of different volatilities from a diesel engine were studied with two tandem differential mobility analyzers (TDMAs) and an aerosol particle mass analyzer (APM). In both TDMA systems, a heater was located in the aerosol path between the first and second DMAs. Diesel exhaust particles that were size-selected in the first DMA were passed through the heater, and the change in particle size due to loss of volatile components was determined by the second DMA. On the basis of the volatility measurements, the particles could be separated into two overlapping modes that varied in peak diameter and magnitude depending on the engine operating conditions. Particles in the smaller size mode were almost completely volatile, while those in the larger size mode contained a nonvolatile core. The TDMA data inversion technique used here allowed accurate determination of the mixing ratios of the two types of particles. These data were in turn used to validate a simple fitting method that uses two log-normal curves to obtain the mixing ratios. In some experiments, the APM was used downstream of a TDMA to directly measure the particle mass loss due to evaporation. The loss determined bythe TDMA-APM system was significantly greater than that calculated from mobility size changes measured solely with the TDMA. The TDMA-APM results were used to calculate the size-dependent mass concentrations of volatile and nonvolatile components for particles in the size range from 70 to 200 nm.
利用两台串联差分迁移率分析仪（TDMA）和气溶胶颗粒质量分析仪（APM）研究了柴油机中不同挥发性颗粒的混合特性。在两个TDMA系统中，加热器位于第一和第二差分迁移率分析仪（DMA）之间的气溶胶路径上。在第一个DMA中进行尺寸选择的柴油机排气颗粒通过加热器，挥发性成分损失导致的颗粒尺寸变化由第二个DMA测定。基于挥发性测量结果，颗粒可分为两种重叠模式，其峰值直径和大小根据发动机运行条件而变化。较小尺寸模式的颗粒几乎完全是挥发性的，而较大尺寸模式的颗粒包含一个非挥发性核心。这里使用的TDMA数据反演技术能够准确测定两种颗粒的混合比。这些数据进而用于验证一种使用两条对数正态曲线来获得混合比的简单拟合方法。在一些实验中，APM用于TDMA的下游，以直接测量由于蒸发导致的颗粒质量损失。由TDMA-APM系统测定的损失显著大于仅用TDMA测量的迁移率尺寸变化所计算出的损失。TDMA-APM的结果用于计算70至200纳米尺寸范围内颗粒的挥发性和非挥发性成分的尺寸相关质量浓度。
