Final Report: Imaging and Classification of Ultrafine Particles in Indoor AirEPA Grant Number: R826688
Title: Imaging and Classification of Ultrafine Particles in Indoor Air
Investigators: Cohen, Beverly S. , Guo, Hai , Heikkinen, Maire SA , Li, Wei , Xiong, Judy Q.
Institution: New York University
EPA Project Officer: Chung, Serena
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $387,384
RFA: Exploratory Research - Human Health (1998) RFA Text | Recipients Lists
Research Category: Health Effects , Human Health , Health
The overall objective of this research project was to utilize morphometric and surface properties of airborne ultrafine particles (diameter < 200 nm) to measure and classify them by source and composition. This will permit measurement of personal exposure to specific indoor and outdoor pollutants and improve estimates of risk. No morphometric data currently is available for indoor particles in this size range, although they constitute more than 90 percent of the number of airborne particles. We hypothesize that distinctive morphometric parameters identified by atomic force microscopy (AFM) will allow the classification of indoor nanometer-sized particles. Further, use of AFM in conjunction with reactive substrates may allow broad chemical classification. An additional objective was to utilize a very low flow personal diffusion monitor prototype under development in our laboratory for simultaneous sampling of ultrafine indoor and outdoor aerosol particles.
Ultrafine Diffusion Monitor (UDM). In the last project year, our efforts focused on improving the UDM for collection of ultrafine airborne particles. The UDM is a relatively quiet and minimally invasive monitor that can be used in homes and indoor public places. We reduced the length of the diffusion channel to produce two short UDMs, and collected aerosol particles both indoors and outdoors in one home and one workplace cafeteria.
Samples Collected Following the World Trade Center Disaster. Because the UDM samplers are simple and lightweight, we were able to quickly deploy several of them at a sampling station close to the site of the September 11, 2001, World Trade Center (WTC) collapse at the earliest possible time access to the area could be arranged. The sampling site was located at the New York University Downtown Hospital (NYUDH) about 3 blocks northeast of the former WTC site now known as "Ground Zero." Six sample sets, consisting of six detectors each, were collected with the UDMs from September 19, 2001September 25, 2001. Both iron nanofilm and silica surface detectors were deployed. The particles collected were compared with UDM samples collected in Manhattan during the winter of 2000, and with particles similarly collected in the fall of 1999 at a rural site in Tuxedo, NY. Thus far, we can detect no differences in the nature of the particles collected on the iron nanofilm detectors during these three intervals using the UDM-AFM system.
Fifteen additional sets of samples for AFM analysis were collected at the WTC site from September 28, 2001-December 20, 2001. Samples were precipitated onto detectors with an Electrical Aerosol Sampler (EAS) preceded by a Mercer Impactor. Only particles that penetrated the 0.47 µm cut size stage of the impactor entered the EAS. Initial scans showed heavy deposits of submicrometer particles that appeared to be agglomerates. The deposits are dense, with large variations in particle size. Significant variability in sample height causes difficulty in setting AFM parameters for proper visualization of acid reaction sites on the iron nanofilm detectors. Further analysis of the remaining samples is underway. However, individual particles and agglomerates are clearly visible on the silicon detectors. The silicon surface is extremely uniform so that deposited particles are easy to visualize. The detectors showed heavy particle deposits with individual particles with diameters of about 100-200 nm.
Collection Efficiency. The airborne concentration of the ultrafine particles can be calculated with knowledge of the size dependent UDM collection efficiency. The efficiency with which the airborne particles are deposited onto the collectors in the UDM has been investigated both theoretically and experimentally. Measurements made with monodisperse 50 and 100 nm fluoroscein aerosols have resulted in higher deposition values than those made with unattached radon progeny. For both sets of measurements, the experimental results exceed theoretical values.
Force-Distance Measurements. In this last year, efforts were undertaken to investigate particle differences using force-distance curves. Measurement of the rate of change of force between the surface and the AFM probe, or tip, as a function of distance was reported as an indicator of surface properties. Problems, as yet unsolved, have been encountered in achieving reproducible contact between the tip and a specific ultrafine particle because of the extraordinarily fine resolution required, and in distinguishing measurable parameters from different substrate surfaces.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 11 publications||2 publications in selected types||All 1 journal articles|
||Cohen BS, Li W, Xiong JQ, Lippmann M. Detecting H+ in ultrafine ambient aerosol using iron nano-film detectors and scanning probe microscopy. Applied Occupational and Environmental Hygiene 2000;15(1):80-89.||