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Size-selective sampling performance of six low-volume “total” suspended particulate (TSP) inlets
Vanderpool, R., J. Krug, S. Kaushik, J. Gilberry, A. Dart, AND C. Witherspoon. Size-selective sampling performance of six low-volume “total” suspended particulate (TSP) inlets. AEROSOL SCIENCE AND TECHNOLOGY. Taylor & Francis, Inc., Philadelphia, PA, 52(1):98-113, (2018).
Ambient samples of particulate matter (PM) are routinely collected for purposes of determining their mass concentrations and chemical constituents, assessing health effects associated with their exposure, determining the effectiveness of PM control strategies, and for determining compliance with regulatory standards designed to protect public health (Dockery et al. 1993, Chow 1995, McMurray 1999, Wilson et al. 2002). Critical to the accurate collection and characterization of ambient PM is the ability of the sampler’s inlet to representatively obtain ambient aerosol samples independent of aerodynamic particle size, wind speed, and wind direction. Ideally, the sampler’s inlet would sample all particles of interest with 100% efficiency independent of sampling conditions, while minimizing the inadvertent intrusion of insects, rain, snow, and other airborne debris. Further, particles aspirated by the inlet would ideally be transported without loss to the sampler’s internal fractionator (if any) and to its collection/sensing zone.
Several low-volume inlets (flow rates ≤ 16.7 liters per minute (Lpm)) are commercially available as components of low-cost, portable ambient particulate matter samplers. Because the inlets themselves do not contain internal fractionators, they are often assumed to representatively sample “total” mass concentrations from the ambient air, independent of aerodynamic particle size and wind speed. To date, none of these so-called “TSP” inlets have been rigorously tested under controlled conditions. To determine their actual size-selective performance under conditions of expected use, wind tunnel tests of six commonly used omnidirectional, low-volume inlets were conducted using solid, polydisperse aerosols at wind speeds of 2, 8, and 24 km/hr. With the exception of axially-oriented, isokinetic sharp-edge nozzles operating at 5 and 10 Lpm, all low-volume inlets showed some degree of non-ideal sampling performance as a function of aerodynamic particle size and wind speed. Depending upon wind speed and assumed ambient particle size distribution, total mass concentration measurements were estimated to be negatively biased by as much as 66%. As expected from particle inertial considerations, inlet efficiency tended to degrade with increasing wind speed and particle size, although some exceptions were noted. The implications of each inlet’s non-ideal behavior are discussed with regards to expected total mass concentration measurement during ambient sampling and the ability to obtain representative sampling for size ranges of interest, such as PM2.5 and PM10. Overall test results will aid in low-volume inlet selection and with proper interpretation of results obtained with their ambient field use.
Record Details:Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
EXPOSURE METHODS & MEASUREMENT DIVISION