Evaluation of Federal Reference Method PM10 Inlet for Sampling Large Particles
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Particulate matter (PM) is one of the six criteria pollutants regulated under the National Ambient Air Quality Standards (NAAQS). Regional compliance with PM NAAQS is monitored using networks of Federal Reference Method (FRM) designated PM10 sampling inlets. Several previous studies have suggested that FRM PM10 inlets sampling PM from rural sources will not perform as designed and that a significant number of particles with larger diameters will penetrate the inlet. This research sought to characterize a common FRM PM10 inlet, the SA246b, using a combination of the original developmental steps, FRM designation testing procedures, and new techniques. The wind tunnel originally used as part of the designing and testing of the SA246b was reassembled and evaluated against Subpart D standards. The SA246b was evaluated as described in Subpart D at a wind speed of 8 km h^-1 with two adjustments: an aerosol particle sizer and testing times were specifically scheduled to meet minimum signal requirements. Measured and corrected data showed that particles with diameters of 20 and 25 micrometers had non-trivial penetration of 5.7% and 3.5%, respectively. A lognormal curve was found to be most descriptive of the collected data (p-value of 0.686). The Subpart D mass concentration analysis yielded a concentration of 152.694 μg m^-3 which was within 10% of the ideal concentration value, 143.889 μg m^-3. When the empirical SA246b lognormal performance curve was applied to the PSDs for several different rural PM sources, the mass concentration values for those sources were between 10% and 34% greater than that of the Subpart D ideal mass concentration. It was determined that the impact of large particle penetration was non-trivial and dependent upon the PSD of the PM being sampled. A low volume total suspended particulate (LVTSP) inlet developed at Texas A&M University was evaluated in the Subpart D wind tunnel in an effort to fully characterize the true performance of the inlet. The inlet was evaluated at wind speeds of 2, 8, and 24 km h^-1 according to the procedures of Subpart D and the experimental additions employed during the SA246b testing. It was determined that piecewise models were more descriptive across all three wind speeds (p-values were greater than 0.84). Data collected in the wind tunnel was shown to be wind speed dependent and no further analysis of inlet performance was conducted. It was concluded that further analysis of the wind tunnel at the wind speeds of two and 24 km h^-1 need to be conducted before further studies could be reliable. Computational fluid dynamics was used to analyze the performance of the impactor section (the lower section) of the SA246b FRM PM10 inlet for the particle sizes listed in Subpart D. The CFD for the impactor assembly produced a cutpoint of 14.79 micrometers and a performance slope of 1.19 resulting in a 34.88% higher mass concentration for CFD results than the ideal Subpart D inlet mass concentration. This result is outside the 10% difference allowed. It was concluded that the characterization of the inlet must include the aspirator as well as the impactor section as the aspirator assembly also has sampling performance characteristics.
Smith, Raleigh Allen (2017). Evaluation of Federal Reference Method PM10 Inlet for Sampling Large Particles. Master's thesis, Texas A & M University. Available electronically from