A critical element of the risk assessment of exposure to airborne ambient ultrafine particles (UFP) is the quantification of respiratory tract deposition (RTD) of the particles, which is intrinsically challenging, particularly at the population scale. In this study, we used a recently proposed method to experimentally determine the RTD of urban UFP in a large group of children exposed to these particles in a school setting in Brisbane, Australia. Children are one of the most susceptible population groups; However, little is known about the deposition of UFP from urban traffic in their airways. In order to advance the knowledge in this field, the objectives of this study were: to determine the deposition of ambient urbane UFP in large number children, to catergorize the source of inhaled UFPs and hence to assess the contribution of air pollution sources to the deposition.

RTD was measured in children aged 8–11 at primary schools using a flow-through chamber bag system. First, the inhaled and exhaled air was separated; then the particle number size distribution and particle number concentration were measured. The sources of inhaled UFP were categorized according to their particle number size distribution by a K means cluster technique.

A total of 128 children from five schools performed the RTD measurement. The mean total deposition fraction of urban UFP in all children was 0.59 ± 0.10. Inhaled UFP were categorized into two groups: traffic and urban background, with the GMD of corresponding particle number size distribution of 20 nm and 40 nm, respectively. The total deposition fraction (mean ± SD) of UFP from these two groups was 0.68 ± 0.09 for traffic and 0.55 ± 0.08 for urban background respectively.

This is the first study in which RTD was measured in a large group of children inhaling real urban UFP. First, we proved that this novel method can indeed be applied easily and quickly to a large group of people. Second, we quantified the RTD of children, thus providing an important input to the risk assessment for exposure to UFP.

暴露于空气传播的环境超细颗粒（UFP）风险评估中的关键要素是颗粒的呼吸道沉积（RTD）量化，这是固有的挑战，尤其是在人口规模上。在这项研究中，我们使用了一种最近提出的方法，通过实验确定了在澳大利亚布里斯班的一大批暴露于这些颗粒的儿童中城市UFP的RTD。儿童是最易受影响的人口群体之一；但是，人们对于城市交通在其气道中沉积UFP的了解很少。为了提高该领域的知识水平，本研究的目标是：确定大量儿童中周围城市UFP的沉积，

RTD是在8-11岁的小学儿童中使用流通室袋系统测量的。首先，将吸入和呼出的空气分开；然后测量颗粒尺寸分布和颗粒浓度。通过K均值聚类技术，将吸入的UFP的来源根据其颗粒大小分布进行分类。

来自五所学校的128名儿童进行了RTD测量。所有儿童中城市UFP的平均总沉积分数为0.59±0.10。吸入的UFP分为两类：交通和城市背景，相应的颗粒数大小分布的GMD分别为20 nm和40 nm。这两组的UFP的总沉积分数（平均值±SD）分别为交通量0.68±0.09和城市背景0.55±0.08。

这是首次对大量吸入真实城市UFP的儿童进行RTD测量的研究。首先，我们证明了这种新颖的方法确实可以轻松，快速地应用于大量人群。第二，我们量化了儿童的RTD，从而为暴露于UFP的风险评估提供了重要的输入。