2000 Progress 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.
Current 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 Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $387,384
RFA: Exploratory Research - Human Health (1998) RFA Text | Recipients Lists
Research Category: Health Effects , Human Health , Health
Objective:The ultimate goal of the research is 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 are 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 Scanning Probe Microscopy (SPM) will allow classification of indoor nanometer-sized particles. Further, use of SPM in conjunction with reactive substrates may allow broad chemical classification. An additional aim is to utilize a prototype very low flow personal diffusion monitor under development in our laboratory for simultaneous sampling of ultrafine indoor and outdoor aerosol particles.
Progress Summary:Reactive Substrates. Building on film substrate development reported last year, particles composed of three organic compounds, dioctyl phthalate (DOP), oleic acid, and 1-octodecanol, were collected on two chemically reactive substrates (i.e., FC724 and C60). When observed under SPM, the DOP particles produced clear circular rings with narrow raised rims on FC724, and smaller diameter rings with much wider raised rims on C60. Oleic acid particles produced holes on both substrates. 1-Octodecanol produced rings with raised centers on FC724, but holes on C60. Thus, combinations of detectors could allow resolution of broad classes of organic particles by observation of different kinds of interaction sites caused by organic particles on different substrates. In one experiment, we exposed the two substrates to indoor particles generated while cooking. Holes were observed on both of the substrates, suggesting the presence of acidic organic particles.
SPM Image Morphometry. Extensive efforts have been made to improve basic calibration information that is needed to obtain quantitative information from SPM images. Height (z) calibration is difficult because few calibration standards are available. The z scanner is nonlinear, so it is important to use a standard that is about the same height as the objects of interest. Calibrations were accomplished using four polystyrene latex microsphere-size standards that were aerosolized and collected on iron-coated or bare silicon substrates. Following collection of 50 nm, 88 nm, 126 nm, and 198 nm polystyrene latex particles, the detectors were examined with SPM in noncontact mode. The height (z) and width (x) of individual particles were measured for calibration. The correlation coefficient (r2) is only 0.422 for x, while it is 0.998 for z. The poor x calibration results from convolution of the tip on the sample surface. To interpret the image correctly it is essential to deconvolve the shape of the tip from the image. This limits the use of topography for particle identification.
Collection Efficiency. The efficiency with which airborne particles are deposited onto collectors in an Electrostatic Aerosol Sampler (EAS) was measured to confirm data provided by the manufacturer because the original calibration data for this instrument were published in 1967. The efficiency must be known to evaluate particle concentrations in air. Three sizes of polystyrene microsphere standards were aerosolized and further size selected with an electrostatic classifier (ESC). The particle concentration entering the EAS was recorded by a condensation particle counter. The value was compared with the airborne particle concentration calculated from the SPM count of deposited particles. The deposition efficiency (± standard deviation) was 0.63±0.08, 0.78±0.09, and 1.02±0.10 for 50 nm, 126 nm, and 198 nm spheres, respectively. The first two values agree with the early reports, the last value is 20 percent higher.
Future Activities:Testing of substrates will continue, as will further development of scanning protocols for morphometric analysis. Evaluation of the particle samples will be tested using SPM force-distance variations and friction forces. Environmental aerosol testing and indoor/outdoor sampling also is planned.
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.||