High-volume diffusion denuder sampler for the routine monitoring of fine particulate matter: I. Design and optimization of the PC-BOSS

Fine particulate mass will frequently be significantly underestimated in urban environments using current EPA federal reference method (FRM) single filter samplers because of loss of semivolatile organic material and nitrate from the particles during sampling. Previously described diffusion denuder samplers, such as the Brigham Young University organic sampling system (BOSS) and BIG BOSS, eliminate both positive and negative sampling artifacts by removing the gas-phase material before fine particulate mass is collected on a quartz filter and a sequential sorbent filter or bed. However, these samplers are not amenable to routine field use because they require multiple systems to accurately account for the efficiency of the denuder for each sample. The denuder efficiency is substantially improved by combining a conventional 2.5 mum cutpoint inlet and a low cutpoint virtual impactor particle concentrator to provide concentrated fine particles (0.1-2.5 mum) to a BOSS diffusion denuder sampling system (PC-BOSS). The performance of both the particle concentrator and the diffusion denuder in the PC-BOSS has been evaluated. Under optimized conditions, the minor to total flow ratio for the concentrator is 25% and the concentrator efficiency is 70-90% for sulfate and 60-85% for soot, depending on the particle size distribution of these species. The particle loss in the concentrator is about 6%. The particle loss in the denuder system is negligible. At the recommended optimum minor flow (concentrated particles, 25% of the total flow), most of the gas-phase material is discarded by the particle concentrator before the concentrated fine particles enter the diffusion denuder. At an optimized inlet flow of 150 L/min with a flow through the denuder of 38 L/min, the overall efficiency of the PC-BOSS for the removal of gas-phase organic material, SO2, and HNO3 is over 99%.