ABSTRACT

Lead species in size-fractionated aerosol particles collected at Higashi-Hiroshima, Japan, were determined by bulk and micro-X-ray absorption fine structure (μ-XAFS) spectroscopy and microbeam X-ray fluorescence (μ-XRF) analysis with thermodynamics calculation. The dominant Pb species in fine aerosol particles were PbSO₄, PbC₂O₄ and Pb(NO₃)₂. The species mixed internally. The Pb species in fine aerosol particles estimated by thermodynamics calculations were consistent with those estimated by XAFS spectroscopy. Results suggest that Pb species in fine aerosol particles were formed by an in-cloud process related to aquatic chemistry. In addition to the in-cloud process, heterogeneous reaction of Pb with NOx, SO₂ and oxalic acid is also an important reaction pathway for dominant Pb species in fine aerosol particles. Lead species in coarse aerosol particles were 2PbCO₃·Pb(OH)₂, Pb(NO₃)₂ and PbC₂O₄. Basic Pb carbonate, a main component of white road paint, the most dominant Pb species. The chemical reaction between 2PbCO₃·Pb(OH)₂ and HNO₃ in the atmosphere forms Pb(NO₃)₂. In addition to these dominant species, μ-XAFS detected minor species overlooked by bulk-XAFS. Thus, the combination of μ-XRF, μ-XAFS, bulk-XAFS and thermodynamics calculation is a powerful strategy for reliable and accurate Pb speciation and source apportionment.