Case Study: What Do Cyclones Collect?

Comparison of Microscopic and Aerodynamic Particle Size for Method 201A Samples or “What Do Cyclones Collect?”

By Tim Vander Wood & Whitney Hill (MVA Scientific Consultants) and Jim Serne (TRC)

Cyclones are commonly used to collect PM10 and PM2.5 size fractions, under the assumption that they accurately separate out particles with diameters above and below 2.5 and 10 micrometers. We have analyzed cyclone fractions collected in the field by automated scanning electron microscopy, directly determining the particle diameters collected on each stage. Examination of these particles indicates that the particle sizes actually collected on each stage range far outside the listed particle size cutoffs. Reconstruction of the actual particle size distributions from the measured particle sizes and mass collected in each cyclone fraction indicates that significant errors may be present in the cyclone data, particularly in the PM2.5 fraction.

CONCLUSION: Mass distributions determined by microscopy on collected cyclone samples indicate that cyclone cutoffs are very wide, and particularly for PM2.5, cyclone collections may greatly overestimate the total mass.

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