Methods for improved size resolution for particle impactors

大气中颗粒物的存在对人类健康有重大影响。 持续暴露于污染物颗粒会导致哮喘、肺癌和慢性阻塞性肺病（COPD）等疾病。 此外，研究表明，急诊室就诊和死亡率与当天空气中的颗粒污染水平相关。 颗粒物的大小对其在肺部的沉积位置以及对健康的影响有显着影响。 例如，微米级颗粒在肺的最深凹处沉积非常有效，而较大的颗粒倾向于存款在上支气管和咽中。 最近，动物研究表明，纳米尺寸的颗粒可以从肺部转移到其他器官，包括大脑。 已经进行了许多研究，测量大气和工业工作环境中颗粒的数量和尺寸分布，目的是了解颗粒的形成和从空气中去除。 粒子计数器是测量和计数直径从几纳米到几百微米的粒子的仪器，是这些研究中不可或缺的工具。 存在在该颗粒直径范围内具有良好尺寸分辨率的颗粒计数器。然而，这种类型的计数器是昂贵的，脆弱的，几乎不便携，因为它们使用激光，真空室和高电压。 一种更便宜、更坚固、更便携的替代方法是称为级联撞击器的设备。不幸的是，这些装置具有差的粒径分辨率，考虑到粒径对人类健康的影响，这是一个显著的问题。 这项研究利用了新发现的撞击器中粒子的物理特性，极大地扩展了它们的测量能力。 成功完成这项研究将使研究，否则将是不可能的。 因此，这项研究可以作为一个力量倍增器，使粒子科学家和流行病学家能够大大扩展他们的能力。 此外，这项工作将导致至少一名研究生和几名本科生在粒子科学领域的培训，这是一个重要的学科，通常不是研究生或本科生工程课程的一部分。撞击级联用于测量和计数空气中的颗粒，用于广泛的应用，包括流行病学研究，监测采矿和建筑等行业的工人暴露，和大气污染的研究。 虽然这些设备可以检测直径小至10 nm的颗粒，但它们的直径分辨率很差。 市售的冲击器级联产生具有至多13个仓的粒度分布（PSD）。 这项研究包括一组计算模拟和实验，将演示如何在单个撞击器级内对颗粒进行尺寸隔离，从而大大提高可从撞击器级联获得的PSD的直径分辨率。 主要研究员的初步研究表明，对撞击器几何形状进行相对较小的修改，可导致撞击器板捕获的颗粒根据其直径分布在板的径向方向上。 也就是说，较大直径的颗粒位于板的中心附近，较小直径的颗粒位于周边附近。 颗粒的这种尺寸分离允许从撞击器级联获得的PSD中的几乎无限数量的箱。 这些初步结果是针对微米级颗粒获得的。 该研究将探索冲击器几何形状的进一步变化，这些变化可以最大限度地提高这种效果，然后证明其有效性，直径小至10 nm。 主要研究者将招募女性和代表性不足的少数民族研究生参加这项研究，并推广到高中学生将是该项目的一部分。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

The presence of particles in the atmosphere has a significant impact on human health. Continued exposure to pollutant particles contributes to ailments such as asthma, lung cancer, and chronic obstructive pulmonary disorder (COPD). In addition, studies have shown that emergency room visits and mortality rates are correlated to the level of particulate pollution in the air on that day. The size of a particle has a significant effect on where it deposits in the lung and therefore on its health impact. For example, micron scale particles are very effective at depositing in the deepest recesses of the lung, while larger particles tend to deposit in the upper bronchial tubes and in the pharynx. Recently, animal studies have shown that nanometer sized particles can translocate from the lungs to other organs, including the brain. Many studies have been conducted which measure the number and size distribution of particles in the atmosphere and in industrial work environments, with the goal of understanding the formation and removal of particles from the air. Particle counters, instruments which size and count particles for diameters ranging from a few nanometers to hundreds of microns, are an indispensable tool in these studies. Particle counters exist which have good size resolution over this range of particle diameters. However, this type of counter is expensive, fragile, and barely portable, as they use lasers, vacuum chambers, and high voltage. A cheaper, more robust, and highly portable alternative is a device called a cascade impactor. Unfortunately, these devices have poor particle diameter resolution, a significant problem given the effect of particle diameter on human health. This research takes advantage of newly discovered physics of particles in impactors to dramatically extend their sizing capabilities. Successful completion of this research will enable studies that would not otherwise be possible. This research therefore serves as a force multiplier, enabling particle scientists and epidemiologists to dramatically extend their capabilities. Additionally, this work will result in the training of at least one graduate student and several undergraduates in the field of particle science, an important discipline that is typically not part of graduate or undergraduate engineering curricula.Impactor cascades are used to size and count particles in air for a large range of applications, including epidemiological studies, monitoring of worker exposure in industries such as mining and construction, and studies of atmospheric pollution. While these devices can sense particles down to diameters as small as 10 nm, their diameter resolution is poor. Commercially available impactor cascades yield particle size distributions (PSDs) having at most 13 bins. This research consists of a set of computational simulations and experiments that will demonstrate how particles can be size-segregated within a single impactor stage, thereby dramatically increasing the diameter resolution of the PSDs that can be obtained from impactor cascades. Preliminary research by the principal investigator has shown that relatively minor modifications of the impactor geometry can cause particles captured by an impactor plate to be distributed in the radial direction of the plate according to their diameter. That is, larger diameter particles are located near the center of the plate and smaller ones near the periphery. This size segregation of particles allows for a virtually unlimited number of bins in PSDs obtained from impactor cascades. These preliminary results were obtained for micron scale particles. The research will explore further variations of the impactor geometry which can maximize this effect and then demonstrate its efficacy down to diameters as small as 10 nm. The principal investigator will recruit female and underrepresented minority graduate students to participate in this research, and outreach to high school students will be part of the project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.