Evaluation of the loading characteristics of the EPA WINSPM2.5 separator

The loading characteristics of the USEPA Well Impactor Ninety Six (WINS) PM 2.5 separator was an important design consideration during the separator's development. In recognition that all inertial separators eventually overloa d, the loading surface of the WINS was designed to be easily accessible, re placeable, and cleanable. Prior to promulgation of the method, the loading capacity of the WINS separator was evaluated by measuring its performance a fter repeated loading with laboratory-generated. high concentration, coarse -mode aerosol. For this purpose, a low flow rate loading wind tunnel was de signed and constructed to artificially create coarse mode aerosols composed of Arizona Test Dust. This controlled test atmosphere was sampled by the P M2.5 reference method sampling train, as specified in 40 CFR Part 50, Appen dix L, at total aerosol mass concentrations averaging 332 mug/m(3) for thre e 24 h periods. The particle size fractionation characteristics of the WINS was evaluated in the laboratory after each 24 h sampling event. These perf ormance curves were integrated with three idealized ambient distributions t o yield estimates of bias in measured mass concentration with respect to a clean WINS. Test results served as the basis for establishing the required cleaning frequency of the sampler during field use. Following the method's promulgation, characterization of the WINS performance under conditions of actual field use at five U.S. cities showed that a maximum mass concentrati on bias of -2.1% was estimated for 13 wells after the 5 day sampling period . Overall study results supported the current regulation (USEPA 1998) that WINS wells be replaced after every 5 days of 24 h operation.