Systematic biases in measured PM10 values with US Environmental ProtectionAgency-approved samplers at Owens Lake, California

From 1993 through 1998, Wedding or Graseby high-volume PM2.5 samplers were collocated with tapered element oscillating microbalance (TEOM) samplers at three sites at Owens Lake, CA. The study area is heavily impacted by windb lown dust from the dry Owens Lake bed, which was exposed as a result of wat er diversions to the city of Los Angeles. A dichotomous (dichot) sampler an d three collocated Partisol samplers were added in 1995 and 1999, respectiv ely. U.S. Environmental Protection Agency (EPA) operating procedures were f ollowed for all samplers, except for a Wedding sampler that was not cleaned for the purpose of this study. On average, the TEOM and Partisol samplers agreed to within 6%, and the dichot, Graseby, and Wedding samplers measured lower PM10 concentrations by about 10, 25, and 35%, respectively. Surprisi ngly, the "clean" Wedding sampler consistently measured the same concentrat ion as the ''dirty" Wedding sampler through 85 runs without cleaning. The f inding that the Graseby and Wedding high-volume PM10 samplers read consiste ntly lower than the TEOM, Partisol, and dichot samplers at Owens Lake is co nsistent with PM10 sampler comparisons done in other fugitive dust areas, a nd with wind tunnel tests showing that sampler cut points can be significan tly lower than 10 mu m under certain conditions. However, these results are opposite of the bias found for TEOM samplers in areas that have significan t amounts of volatile particles, where the TEOM reads low due to the vapori zation of particles on the TEOM's heated filter. Coarse particles like fugi tive dust are relatively unaffected by the filter temperature. This study s hows that in the absence of volatile particles and in the presence of fugit ive dust, a different systematic bias of up to 35% exists between samplers using dichot inlets and high-volume samplers, which may cause the Graseby a nd Wedding PM10 samplers to undermeasure PM10 by up to 35% when the PM10 is predominantly from coarse particulate sources.