Particulate testing was performed at scrubber-equipped and ESP-equipped, coalfired power plants. The particulate collecting portion of each train was followed by an EPA Method 8 train to determine the amount of sulfuric acid mist and sulfur dioxide that passed through the particulate filter. Significant quantities of a volatile sulfate were found in the Method 5 particulate sample even when the probe and filter were maintained at a temperature 30 C above the acid dewpoint. It was also found that: (1) Heating the collected sample at temperatures above the sampling temperature would effectively remove this material from the ESP-equipped plant samples, but not from the scrubber-equipped plant samples; (2) At the ESP-equipped plant, the Alundum thimble particulate results were equivalent to Method 5, but at the scrubber-equipped plant were considerably higher; (3) At both sources, borosilicate glass-fiber thimble filters gave average particulate results that were considerably higher than Method 5 and would not release most of this excess weight when heated to 316 C; and (4) A combination Method 5/Method 8 train cannot be used to simultaneously measure particulate and sulfuric acid at these sources unless the probe and filter are operated at a temperature much higher than the 160 C now specified by regulation.