Comprehensive field studies were conducted to evaluate the performance of sampling methods for measuring the coarse fraction of PM (sub 10) in ambient air. Five separate sampling approaches were evaluated at each of three sampling sites. As the primary basis of comparison, a discrete difference method was used which employs two designated FRM samplers, one to measure PM (sub 2.5) and the other PM (sub 10). The numerical difference of these reference method concentrations (PM (sub 10)-PM (sub 2.5)) represented an estimate of PMc. A second sampling approach involved a sequential dichotomous sampler, which provided both PM (sub 2.5) and PMc measurements. In both of these filter-based, time-integrated measurement approaches, the collected aerosol mass was analyzed gravimetrically in the laboratory under controlled conditions. The third real-time sampler evaluated was an aerodynamic particle sizer (APS) that measures the aerodynamic diameter of individual particles, calculates the mass of the particle based on an assumed particle density, and then sums the mass within the size range of interest to estimate the PMc mass concentration.