US EPA

Measurement of the mass and composition of particulate matter (PM) as a function of size is important for research studies for chemical mass balance, factor analysis, air quality model evaluation, epidemiology, and risk assessment. Such measurements are also important in understanding the relationships between personal exposure, indoor concentrations, and outdoor concentrations. Fine-mode and coarse-mode particles differ in sources, composition, and properties. The overlap of fine-mode and coarse-mode particles in PM2.5 may cause difficulty in interpretation of the data. The hypothesis is advanced that the intrusion of coarse-mode material into the fine mode will cause more problems than the intrusion of fine- mode material into the course mode. To the extent that this hypothesis is true, a cut-point between 1 and 1.5 m aerodynamic diameter will provide a better separation of fine- and coarse-mode particles than a cut-point of 2.5 m aerodynamic diameter.

Wilson, W. Size Distribution Of Ambient And Indoor Particles: Does The Overlap Of Fine And Coarse Particles Cause Problems In The Interpretation Of Research Results? Presented at AWMA Specialty Conference, PM 2000, Charleston, SC, January 2000.