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Limits of detection and artifact formation of sulfates and nitrates collected with a triple-path denuder

Atmospheric Environment
Publication Date
DOI: 10.1016/1352-2310(94)90399-9


Abstract Ammonium sulfate and nitrate aerosols were generated and sampled on Teflon (PTFE) filters in a triple-path denuder (TPD) at the Research Triangle Institute. Lower limits of detection and quantitative analysis of the resulting samples were completed by X-ray diffraction at the South Dakota School of Mines and Technology. Denuder coatings included oxalic 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 μg m −3 for (NH 4) 2SO 4 (mascagnite), and 10 μg m −3 for NH 4NO 3 were generated by a nebulizer and introduced to the instrument's PM 10 sampling 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 collections on the filters varied from 0.9 to (as high as) 22 for extremely light filter loadings. Spalling of the oxalic acid coating along denuder A and contamination of the aerosol in the collection cassette resulted in an initially rapid but decaying rate of artifact reaction of the mascagnite to letovicite (NH 4) 3H(SO 4) 2 over several months of laboratory storage. No analogous reaction was observed for the NH 4NO 3 aerosol samples.

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