Zelenyuk Alla, Yang Juan, Song Chen, Zaveri Rahul A, Imre Dan
Pacific Northwest National Laboratory, Richland, WA 99354, USA.
Environ Sci Technol. 2008 Nov 1;42(21):8033-8. doi: 10.1021/es8013562.
Particle volumes are most often obtained by measuring particle mobility size distributions and assuming that the particles are spherical. Particle volumes are then converted to mass loads by using particle densities that are commonly estimated from measured mobility and vacuum aerodynamic diameters, assuming that the particles are spherical. For aspherical particles, these assumptions can introduce significant errors. We present in this work a new method that can be applied to any particle system to determine in real time whether the particles are spherical or not. We use our second-generation single particle mass spectrometer (SPLAT II) to measure with extremely high precision the vacuum aerodynamic size distributions of particles that are classified by differential mobility analyzer and demonstrate that the line shape of these vacuum aerodynamic size distributions provide a way to unambiguously distinguish between spherical and aspherical particles. Moreover, the very same experimental system is used to obtain the size, density, composition, and dynamic shape factors of individual particles. We present an application of this method to secondary organic aerosols that are formed as a result of ozonolysis of alpha-pinene in the presence and absence of an OH scavenger and find these particles to be spherical with densities of 1.198 +/- 0.004 and 1.213 +/- 0.003 g cm(-3), respectively.
颗粒体积通常是通过测量颗粒迁移率尺寸分布并假设颗粒为球形来获得的。然后，通过使用通常根据测量的迁移率和真空空气动力学直径估算的颗粒密度，将颗粒体积转换为质量负荷，同样假设颗粒为球形。对于非球形颗粒，这些假设可能会引入显著误差。我们在这项工作中提出了一种新方法，该方法可应用于任何颗粒系统，以实时确定颗粒是否为球形。我们使用第二代单颗粒质谱仪（SPLAT II）以极高的精度测量由差分迁移率分析仪分类的颗粒的真空空气动力学尺寸分布，并证明这些真空空气动力学尺寸分布的线形提供了一种明确区分球形和非球形颗粒的方法。此外，使用同一实验系统来获取单个颗粒的尺寸、密度、组成和动态形状因子。我们将此方法应用于在有和没有OH清除剂的情况下α-蒎烯臭氧分解形成的二次有机气溶胶，发现这些颗粒是球形的，密度分别为1.198±0.004和1.213±0.003 g cm⁻³。
