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Passive Aerosol Sampler To Estimate Long-Term Average Concentrations and Size Distributions
EPA Grant Number: U915321Title: Passive Aerosol Sampler To Estimate Long-Term Average Concentrations and Size Distributions
Investigators: Wagner, Jeffrey R.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Jones, Brandon
Project Period: June 1, 1998 through May 1, 2000
Project Amount: $50,059
RFA: STAR Graduate Fellowships (1998) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Engineering , Engineering and Environmental Chemistry , Academic Fellowships
Objective:
The objective of this research project is to develop a miniature, passive aerosol sampler to estimate long-term average concentrations and size distributions. The passive sampler will monitor indoor or outdoor aerosols over a period of weeks, and will have potential utility as a personal sampler.
Approach:
Particles collect by gravity, convective diffusion, and inertia in a small cavity of the passive sampler. Scanning electron microscopy and automated image analysis are used to count and size collected particles with dp > 0.1 µm. Alternatively, more advanced techniques can be used for ambient-pressure analysis or elemental characterization. The measured particle flux and a particle size-dependent deposition velocity model are used to calculate the average concentration and size distribution over the sampling period. To determine the empirical portion of the deposition velocity model and test sampler precision, a special wind tunnel was developed. The small-scale tunnel incorporates a nonvolatile, polydisperse, high-output aerosol generator. An eight-stage impactor is connected to the tunnel with an isoaxial, isokinetic probe, and is equipped with oleic acid-saturated, polycarbonate-membrane substrates to minimize particle bounce. The empirical factor was determined as a function of particle size by minimizing error with respect to impactor mass and size measurements. Precision and accuracy were assessed as a function of wind speed, relative humidity, and aerosol concentration level. In addition, the precision and accuracy of the passive sampler will be tested in field studies under more realistic, fluctuating conditions.