LIMITS OF DETECTION AND ARTIFACT FORMATION OF SULFATES AND NITRATES COLLECTED WITH A TRIPLE-PATH DENUDER

Ammonium sulfate and nitrate aerosols were generated and sampled on Te flon (PTFE) filters in a triple-path denuder (TPD) at the Research Tri angle Institute. Lower limits of detection and quantitative analysis o f the resulting samples were completed by X-ray diffraction at the Sou th Dakota School of Mines and Technology. Denuder coatings included ox alic acid for removal of ammonia, and NaCl for capture of nitric acid; a third path was left uncoated. Primary aerosol concentrations of 17 and 79 mug m-3 for (NH4)2SO4 (mascagnite), and 10 mug m-3 for NH4NO3 w ere generated by a nebulizer and introduced to the instrument's PM10 s ampling inlet under a Tedlar chamber. Monitoring of generated species during collection at RTI was conducted using ion chromatography. Lower limits of detection (LLD, as wt%) for the sulfate and nitrate collect ions on the filters varied from 0.9 to (as high as) 22 for extremely l ight filter loadings. Spalling of the oxalic acid coating along denude r A and contamination of the aerosol in the collection cassette result ed in an initially rapid but decaying rate of artifact reaction of the mascagnite to letovicite (NH4)3H(SO4)2 over several months of laborat ory storage. No analogous reaction was observed for the NH4NO3 aerosol samples.