The characteristics of fugitive dust emitted from vehicles traveling on unpaved dirt roads were measured using a suite of instruments including a real-time fugitive dust sampler. The fugitive dust sampler is formed from a combination of a large particle inlet and an optical particle spectrometer that reports particle sizes from 6 to 75 mm. The large particle inlet permits the sampling of particles up to 75 mm with only a moderate dependence of sampling efficiency on wind-speed. Measurements made with the sampler showed that particles as large as »50 mm were suspended from vehicular movement on the dirt roads, with the mode of the fugitive dust particle number size distribution »2 mm, while the mass distribution mode was »7 mm. A comparison of the fugitive dust sampler measurements with those made using standard PM instruments showed that the conventional instruments have a wind-direction bias that can result in under-sampling of large particles. The current measurements suggest that particles suspended from dirt roadways are of importance for local air quality within the near-road environment.
a b s t r a c tThe sampling performance characteristics of a funnel-shaped large particle inlet (LPI) were obtained experimentally using wind-tunnel measurements and the results compared against computational fluid dynamics (CFD) predictions. In the wind-tunnel, a moving injector system was used to inject polydisperse particles uniformly over the tunnel cross-section and a pair of Aerodynamic Particle Sizers were used to measure sizeresolved sampling efficiencies of the inlet at 3 m s À 1 . The wind-tunnel results differed from earlier published CFD predictions, necessitating a numerical re-analysis of the inlet performance with a higher order turbulence model and a finer mesh grid appropriate for accurate particle turbulent dispersion modeling. The new simulations revealed non-uniformity in the spatial distribution of particles exiting the inlet. As particle measurements were only made from a sub-set of the inlet flow, the spatial distribution of particles needed to be considered for an accurate comparison with numerical simulations. Accounting for the spatial non-uniformity of particles exiting the inlet resulted in reasonably good comparison of simulations with experimental data. The simulation results suggest that the current LPI design results in an almost wind-speed independent sampling performance for particles smaller than 10 mm and a cut-size of $ 20 mm for wind-speeds as large as 4.5 m s À 1 . The CFD results suggest that a simple redesign will result in effective sampling of larger particles but will increase the wind-speed dependence of the inlet's sampling efficiency. Further wind-tunnel testing is required to validate the predicted sampling efficiencies at larger sizes and higher wind-speeds.
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