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DESIGN AND CALIBRATION OF THE EPA PM 2.5 WELL IMPACTOR NINETY-SIX (WINS)
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).
Impact/Purpose:
The core aerosol research for FY01 includes evaluation of newly developed and developing methods for the chemical analysis and sampling of PM in ambient air, especially state-of-the-art continuous and non-invasive aerosol measurement methods, and the study of the aerosol sampling processes to better assess the true aerosol concentration and size distributions observed in the ambient environment. An additional emphasis is placed on integrated sampling for stable and semi-volatile organic aerosol species. This latter area addresses the state-of-the-art in this measurement area. This program supports Title I of the Clean Air Act in its mandate for performing research to support the NAAQS, GPRA goal 1.1.5, and ORD's main research objective on PM.
Much of this work directly supports OAQPS and may be applied within the Supersites Program managed jointly by OAQPS and ORD. This research also will support many of ORD's long-term research goals by providing more reliable information (decrease uncertainty) on ambient aerosols that can be utilized for characterizing risk.
Finally, an APM, has been established to develop measurement methods for causal factors, due in 2004. Currently, there are a number of causal factor hypotheses, but none have sufficient evidence to support developing one measurement/analytical method over another. The PM methods team will support and work with Joellen Lewtas on methods for the collection and analysis of semi-volatile and aerosol phase organic species to help address this APM. The PM methods team will continue to work within the Supersites program and with OAQPS and their new partners in ORIA to further evaluate continuous species specific methods and aerosol physical property measurement methods.
Description:
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.