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Design and Calibration of the EPA PM 2.5 Well Impactor Ninety-Six (Wins)

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Abstract: The EPA well-type impactor ninety-six (WINS) was designed and calibrated to serve as a particle size separation device for the EPA reference method sampler for particulate matter under 2.5 um aerodynamic diameter. The WINS was designed to operate downstream of a PM10 inlet at a volumetric flowrate of 16.7 Lpm. For design simplicity and ease of construction, fractionation of the aerosol in the WINS is provided by a single-stage, single-jet, round-hole impactor. Particles greater than 2.5 um (aerodynamic diameter) have sufficient inertia to be impacted upon a circular 37 mm diameter glass fiber filter immersed in 1 mL of a low volatility oil. The relatively large amount of oil is intended to minimize substrate overloading and subsequent particle bounce experienced by some conventional impactors and to represent an easily field dispensable quantity of defined tolerance. The novel geometry of the impaction reservoir (or well) is designed to capture any reentrained material from the impaction surface and to prevent loss of oil should the unit be inadvertently turned over or on its side. The penetration curve of the final WINS design has a 50 percent cutpoint diameter equal to 2.48 um and a geometric standard deviation of 1.18.

During development, several nozzle designs and well geometries were evaluated to optimize the performance of the WINS. Additionally, two candidate oils (Neovac and Dow Corning 704 diffusion pump oils) and three types of filters (glass fiber filters, drain discs, and polycarbonate membrane filters) were evaluated for use as impaction substrates in the WINS. The performance of the WINS was similar for the two oils in combination with a glass fiber filter and a drain disc; however, a polycarbonate filter demonstrated elevated penetration values. Based on these tests, a Gelman Type A/E glass fiber filter immersed in Dow Corning 704 diffusion pump oil was selected as the best impaction substrate. Further testing showed that the penetration curve was essentially the same when operated with quantities of oil ranging from 0.75 to 3 mL.

This work was conducted by Research Triangle Institute with support provided by the U.S. Environmental Protection Agency through contract no. 68-D5-0040. It has been reviewed in accordance with the Agency's peer and administrative review policies and approved for presentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendation by RTI or the Agency.
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Citation:Peters, T., R. W. Vanderpool, and R. W. Wiener. Design and Calibration of the EPA PM 2.5 Well Impactor Ninety-Six (Wins). AEROSOL SCIENCE AND TECHNOLOGY 34(5):389-397, (2001).
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Contact: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov
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Division: Human Exposure & Atmospheric Sciences Division
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Branch: Atmospheric Methods & Monitoring Branch
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Product Type: Journal
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Published: 05/01/2001
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Related Entries:
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Bullet Item Heasd PM Research Methods: Particle Methods Evaluation and Development
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Last Updated on Monday, October 22, 2007
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