Methods for improved size resolution for particle impactors

Clemson University, Clemson SC

Investigators

Abstract

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.