Nitrogen and sulfur compounds in coastal Antarctic fine aerosol particles—an insight using non-destructive X-ray microanalytical methods

The capabilities of X-ray microanalytical methods, such as a near edge X-ray absorption fine structure (NEXAFS) investigation in conjunction with total reflection X-ray fluorescence (TXRF) analysis, as well as low- Z particle electron probe X-ray microanalysis (EPMA) to characterize fine Antarctic aerosol samples are demonstrated. Both techniques provided information on low- Z elements such as C, N and O. Size-segregated fine aerosol samples were collected at the Italian base at Terra Nova Bay (Antarctica) in February 2004. For comparative purposes, aerosol samples were also collected near the sea-shore in Alghero (Sardinia, Italy), in June 2004. The TXRF-NEXAFS measurements were carried out at the PGM monochromator beamline for undulator radiation in the PTB laboratory at the electron storage ring BESSY II. It was possible to quantify the molar ratio of ammonium and nitrate based on linear combinations of standard reference spectra of (NH 4) 2SO 4 and NaNO 3. Using TXRF-NEXAFS, the ammonium-to-nitrate ratio was determined in Antarctic fine aerosols collected from less than 2 m 3 of air, i.e. considerably lower than the sampling volumes usually used for ion chromatography analyses (30 m 3). This reduced sampling volume can enable the characterization of Antarctic aerosols to be done in higher temporal resolution. For Antarctic fine aerosols in the size range of 0.25–0.5 μm, nitrogen was observed to be present as almost entirely ammonium species. When the size of aerosol particles increases in the range of 0.25–2 μm, the content of ammonium decreases and yet the content of nitrate increases. An aerosol sample collected at Terra Nova Bay was investigated by the use of low- Z particle EPMA at a liquid nitrogen temperature in order to minimize beam damage of nitrogen-rich particles. Single-particle analytical results of 160 individual particles supported the TXRF-NEXAFS's observation that both ammonium-rich and nitrate-rich particles exist in the size range of 1–2 μm. Some particles were observed to contain both ammonium and nitrate species and yet pure ammonium nitrate particles were not encountered. The stoichiometry of the main chemical component of particles containing nitrogen and sulfur as major elements was found to be NH 4HSO 4.