The operation of laser printers can lead to the emission of high numbers of ultrafine particles. Evidence on the toxicology and adverse health effects of these particles has been mounting, however few studies have investigated the complexity of these particles in terms of their volatility, hygroscopicity and mixing state. This study utilized a Volatility Hygroscopic Tandem Differential Mobility Analyzer (VH-TDMA) to explore the internal and external mixing states of printer-generated particles. Up to 6.0 × 10⁵ particles. cm⁻³ were observed during the operation of the laser printer, and these ultrafine particles could be classified into three groups, each with its own particular volatility (i.e., gradually shrinkable, suddenly shrinkable and expandable), owing to the different internal mixing states. In particular, we propose shell-core structures to explain the special volatility of these particles. In addition, whilst the majority of the generated particles were initially hydrophobic at 90% relative humidity (RH), it was observed that there were a very small number of volatilized particles (less than 5%) that shrank (i.e., decreased in size) after humidification. This study can be used as a model for investigating the complex particle formation processes in relation to secondary organic aerosols from other sources. Furthermore, our results shed light on the complexity of indoor aerosols, which should be investigated further in future indoor air quality studies.

激光打印机的运行会导致大量超细颗粒的排放。关于这些颗粒的毒理学和不利健康影响的证据越来越多，但很少有研究调查这些颗粒在挥发性、吸湿性和混合状态方面的复杂性。本研究利用挥发性吸湿串联微分迁移率分析仪 (VH-TDMA) 来探索打印机生成粒子的内部和外部混合状态。高达 6.0 × 10 ⁵颗粒。厘米^-3在激光打印机运行过程中观察到，这些超细颗粒可分为三组，由于内部混合状态不同，每组都有其特定的挥发性（即逐渐收缩、突然收缩和可膨胀）。特别是，我们提出了壳核结构来解释这些粒子的特殊挥发性。此外，虽然大多数生成的颗粒最初在 90% 的相对湿度 (RH) 下是疏水的，但观察到有极少量的挥发颗粒（小于 5%）收缩（即尺寸减小）加湿后。这项研究可用作研究与其他来源的二次有机气溶胶相关的复杂颗粒形成过程的模型。此外，