AbstractCollection of particles on a filter results in underestimation of particulate organic compounds due to losses from the semivolatile organic fraction during sample collection, that is, a “negative sampling artifact.” This sampling-induced change in the phase distribution of semivolatile organic material resulted in the loss of an average of 35% of the particulate organic material in samples collected at the South Coast Air Quality Management District (SCAQMD) sampling site at Azusa, CA, in the Los Angeles Basin. These semivolatile organic compounds lost from particles were measured using two diffusion denuder sampling systems. A multichannel diffusion denuder sampling system (BOSS) was used to determine the concentrations of fine particulate carbonaceous material, and a multisystem, multichannel, high-volume diffusion denuder sampler (BIG BOSS) was used for the determination of the particle size distribution and chemical composition of semivolatile organic compounds in fine particles. Results obtai...